Author name code: hubeny
ADS astronomy entries on 2022-09-14
author:"Hubeny, Ivan" 
------------------------------------------------------------------------  

Title: Properties of Primitive Galaxies
Authors: Heap, Sara R.; Hubeny, I.; Bouret, J. -C.; Lanz, T.;
   Brinchmann, J.
Bibcode: 2022arXiv220704553H
Altcode:
  We report on a study of 9 nearby star-forming, very low-metallicity
  galaxies observed by Hubble's COS far-UV spectrograph that can serve
  as templates of high-z galaxies to be observed by JWST. We find
  that the nebular spectra of these primitive galaxies show evidence
  of irradiation by X-ray emitters. Following Thuan et al. (2004),
  we identify the sources of X-ray emission as massive X-ray binaries
  containing a massive accreting stellar black hole. We further find
  that the lower the metallicity, the higher the probability of strong
  X-irradiation. Following Heger et al. (2003), we suggest that these
  accreting black holes are produced by direct collapse of stars having
  initial masses greater than $\sim50\, M_\odot$. Our models of young
  star clusters with an embedded stellar black hole produce effects on
  the surrounding gaseous medium that are consistent with the observed
  spectra. We conclude that primitive galaxies are qualitatively different
  from more metal-rich galaxies in showing evidence of hard radiation
  that can best be explained by the presence of one or more embedded
  stellar black holes.

Title: How Do Spitzer IRAC Fluxes Compare to HST CALSPEC?
Authors: Bohlin, Ralph C.; Krick, Jessica E.; Gordon, Karl D.;
   Hubeny, Ivan
Bibcode: 2022AJ....164...10B
Altcode: 2022arXiv220508322B
  An accurate tabulation of stellar brightness in physical units is
  essential for a multitude of scientific endeavors. The HST/CALSPEC
  database of flux standards contains many stars with spectral coverage
  in the 0.115-1 μm range, with some extensions to longer wavelengths of
  1.7 or 2.5 μm. Modeled flux distributions to 32 μm for calibration of
  JWST complement the shorter-wavelength HST measurements. Understanding
  the differences between IRAC observations and CALSPEC models is
  important for science that uses IR fluxes from multiple instruments,
  including JWST. The absolute flux of Spitzer IRAC photometry at 3.6-8
  μm agrees with CALSPEC synthetic photometry to 1% for the three prime
  HST standards: G191B2B, GD153, and GD71. For a set of 17-22 A-star
  standards, the average IRAC difference rises from agreement at 3.6 μm
  to 3.4% ± 0.1% brighter than CALSPEC at 8 μm. For a smaller set of
  G-type stars, the average of the IRAC photometry falls below CALSPEC
  by as much as 3.7% ± 0.3% for IRAC1, while one G-type star, P330E,
  is consistent with the A-star ensemble of IRAC/CALSPEC ratios.

Title: WD 1145+017: Alternative models of the atmosphere, dust clouds,
    and gas rings
Authors: Budaj, J.; Maliuk, A.; Hubeny, I.
Bibcode: 2022A&A...660A..72B
Altcode: 2022arXiv220307520B
  Context. WD 1145+017 (WD1145) is the first white dwarf known to be
  orbited by disintegrating exoasteroids. It is a DBZ-type white dwarf
  with strongly variable broad circumstellar lines and variable shallow
  ultraviolet (UV) transits. Various models of the dust clouds and gaseous
  rings have been proposed as an explanation for this behavior. <BR />
  Aims: We aim to revisit these observations and propose alternative
  or modified models of the atmosphere of this white dwarf, its dust
  clouds, and gas rings. <BR /> Methods: The simple radiative transfer
  code Shellspec was modified for this purpose and used for testing
  the new dust cloud and gas disk models. We used modified TLUSTY
  and SYNSPEC codes to calculate atmosphere models assuming the local
  thermodynamical equilibrium (LTE) or nonLTE (NLTE), and to calculate
  the intrinsic spectrum of the star. We then used these atmosphere
  models to estimate the mass of the radiative and convective zones and
  NLTE spectrum synthesis to estimate their chemical composition. <BR />
  Results: We offer an alternative explanation of some (not all) shallow
  UV transits. These may be naturally caused by the optical properties of
  the dust grains: opacities and mainly phase functions as a result of the
  forward scattering. The latter is much stronger in UV compared to the
  optical region, leaving more UV photons in the original direction during
  the transit. We also developed an alternative model of the gaseous disk,
  consisting of an inner, hotter, and almost circular disk and an outer,
  cooler, and eccentric disk. The structure precesses with a period of
  3.83 ± 0.12 yr. We demonstrate that it fits the observed circumstellar
  lines reasonably well. These alternative models solve a few drawbacks
  that might be associated with the previous models, but they also have
  their own disadvantages. We confirm that the chemical composition of
  the atmosphere is similar to that of CI chondrites but carbon, nitrogen,
  and sulfur are significantly underabundant and much closer to the bulk
  Earth composition. This is a strong argument that the star has recently
  encountered and accreted material from a body of Earth-like composition.

Title: High Resolution Spectroscopy of the Unusual Spectral Feature
    in the Central Compact Object PSR J0821-4300
Authors: Gotthelf, Eric; Bogdanov, Slavko; Paerels, Frits; Groger,
   John; Helfand, David; Halpern, Jules; Hubeny, Ivan; Lanz, Thierry
Bibcode: 2022HEAD...1911006G
Altcode:
  We present Chandra LETG high-resolution X-ray spectroscopy of the
  unusual line feature seen in the blackbody emission from the central
  compact object (CCO) in supernova remnant (SNR) Puppis~A. This feature
  is likely associated with one of the antipodal hot-spots on the NS
  surface and may provide the first detection of atomic photospheric
  absorption lines, allowing a model independent, direct measurement of
  the mass-radius relation, a strong constrain on the equation of state
  of nuclear matter. If generated by cyclotron resonance scattering or
  possibly from accretion of supernova debris, the line emission may
  provide a localized measurement of the magnetic field, important for
  reconciling the observed bright surface hot-spots unprecedented for
  a neutron star with such a weak (2.8E-10 G) dipole magnetic field.

Title: Accurate Metallicities for Very Metal-poor Stars from the Ca
    II Infrared Triplet
Authors: Osorio, Yeisson; Aguado, David S.; Prieto, Carlos Allende;
   Hubeny, Ivan; González Hernández, Jonay I.
Bibcode: 2022ApJ...928..173O
Altcode: 2022arXiv220301257O
  The Ca II H and K lines are among the few features available to infer
  the metallicity of extremely metal-poor stars from medium-resolution
  spectroscopy. Unfortunately, these lines can overlap with absorption
  produced in the intervening interstellar medium, introducing systematic
  errors in the derived metallicities. The strength of the Ca II infrared
  triplet lines can also be measured at extremely low metallicities,
  and it is not affected by interstellar absorption, but it suffers
  significant departures from local thermodynamic equilibrium (LTE). We
  investigate the feasibility of adopting the Ca II infrared triplet as a
  metallicity indicator in extremely metal-poor stars using state-of-the
  art non-LTE models including the most recent atomic data. We find
  that the triplet lines exhibit non-LTE abundance corrections that
  can exceed 0.5 dex. When interstellar absorption affecting the Ca II
  resonance lines is accounted for using high-resolution observations,
  the agreement between non-LTE abundances for the triplet and those
  for the resonance lines, with only minor departures from LTE, is
  excellent. Non-LTE effects strengthen the Ca II IR triplet lines,
  facilitating measurements at very low metallicities, compared with LTE
  estimates, down to [Fe/H] = -6.0. This result has important implications
  for the discovery of primitive stars in our Galaxy and others, since
  instruments are most sensitive at red/near-infrared wavelengths, and
  tens of millions of spectra covering the Ca II IR triplet will soon
  become available from the Gaia, DESI, WEAVE, and PFS missions.

Title: The Photospheric X-ray Spectrum of the Neutron Star in Puppis A
Authors: Groger, John; Paerels, Frits; Gotthelf, Eric; Halpern, Jules;
   Helfand, David; Bogdanov, Slavko; Hubeny, Ivan; Lanz, Thierry
Bibcode: 2022HEAD...1910107G
Altcode:
  We have collected 352.6 ksec (as of September 7, 2021) of a 400 ksec
  Chandra observation of the central compact object PSR J0821-4300
  in the supernova remnant Puppis A using the Low Energy Transmission
  Grating Spectrometer. We have clearly detected photospheric radiation
  from the neutron star with a temperature of approximately 2 million
  degrees. We anticipate that we will have the sensitivity to detect
  absorption features from highly-ionized metals that may be present at
  the surface of the star. In this poster, we discuss our preliminary
  analysis of the spectral data.

Title: The Neutron Star in Puppis A: Atomic Photospheric Spectroscopy
    at Last?
Authors: Paerels, Frits; Groger, John John; Helfand, David; Bogdanov,
   Slavko; Gotthelf, Eric; Halpern, Jules; Hubeny, Ivan; Lanz, Thierry
Bibcode: 2022HEAD...1910106P
Altcode:
  We have accumulated 400 ksec of exposure time with the Chandra Low
  Energy Transmission Grating Spectrometer on the neutron star in the
  supernova remnant Puppis A. We clearly detect photospheric radiation
  from a ~ 2 million degree star. We anticipate that the spectrum will
  have sufficient sensitivity for us to detect atomic absorption features
  from highly ionized mid-Z atoms, which may be present at the surface
  of the star. We discuss the data and our preliminary spectroscopic
  analysis.

Title: Simulation of Stark-broadened Hydrogen Balmer-line Shapes
    for DA White Dwarf Synthetic Spectra
Authors: Cho, P. B.; Gomez, T. A.; Montgomery, M. H.; Dunlap, B. H.;
   Fitz Axen, M.; Hobbs, B.; Hubeny, I.; Winget, D. E.
Bibcode: 2022ApJ...927...70C
Altcode:
  White dwarfs (WDs) are useful across a wide range of astrophysical
  contexts. The appropriate interpretation of their spectra relies on the
  accuracy of WD atmosphere models. One essential ingredient of atmosphere
  models is the theory used for the broadening of spectral lines. To date,
  the models have relied on Vidal et al., known as the unified theory
  of line broadening (VCS). There have since been advancements in the
  theory; however, the calculations used in model atmosphere codes have
  only received minor updates. Meanwhile, advances in instrumentation
  and data have uncovered indications of inaccuracies: spectroscopic
  temperatures are roughly 10% higher and spectroscopic masses are roughly
  0.1 M <SUB>⊙</SUB> higher than their photometric counterparts. The
  evidence suggests that VCS-based treatments of line profiles may be at
  least partly responsible. Gomez et al. developed a simulation-based
  line-profile code Xenomorph using an improved theoretical treatment
  that can be used to inform questions around the discrepancy. However,
  the code required revisions to sufficiently decrease noise for use in
  model spectra and to make it computationally tractable and physically
  realistic. In particular, we investigate three additional physical
  effects that are not captured in the VCS calculations: ion dynamics,
  higher-order multipole expansion, and an expanded basis set. We also
  implement a simulation-based approach to occupation probability. The
  present study limits the scope to the first three hydrogen Balmer
  transitions (Hα, Hβ, and Hγ). We find that screening effects and
  occupation probability have the largest effects on the line shapes and
  will likely have important consequences in stellar synthetic spectra.

Title: All-Order Full-Coulomb Quantum Spectral Line-Shape Calculations
Authors: Gomez, T. A.; Nagayama, T.; Cho, P. B.; Zammit, M. C.;
   Fontes, C. J.; Kilcrease, D. P.; Bray, I.; Hubeny, I.; Dunlap, B. H.;
   Montgomery, M. H.; Winget, D. E.
Bibcode: 2021PhRvL.127w5001G
Altcode:
  Understanding how atoms interact with hot dense matter is essential for
  astrophysical and laboratory plasmas. Interactions in high-density
  plasmas broaden spectral lines, providing a rare window into
  interactions that govern, for example, radiation transport in
  stars. However, up to now, spectral line-shape theories employed
  at least one of three common approximations: second-order Taylor
  treatment of broadening operator, dipole-only interactions between
  atom and plasma, and classical treatment of perturbing electrons. In
  this Letter, we remove all three approximations simultaneously for
  the first time and test the importance for two applications: neutral
  hydrogen and highly ionized magnesium and oxygen. We found 15%-50%
  change in the spectral line widths, which are sufficient to impact
  applications including white-dwarf mass determination, stellar-opacity
  research, and laboratory plasma diagnostics.

Title: The Stars Like Dust: Inferring a Probabilistic Extinction
    Law from STIS UV Spectroscopy of the Cosmic Flux Standards
Authors: Narayan, Gautham; Calamida, Annalisa; Axelrod, Tim; Bohlin,
   Ralph C.; Deustua, Susana E.; Holberg, Jay B.; Hubeny, Ivan; MacKenty,
   John W.; Matheson, Thomas; Olszewski, Edward W.; Points, Sean D.;
   Rauch, Thomas; Rest, Armin; Sabbi, Elena; Saha, Abhijit; Stubbs,
   Christopher W.
Bibcode: 2021hst..prop16764N
Altcode:
  Our understanding of dust, encoded in our knowledge of the extinction
  law, is one of the leading sources of systematic bias impacting
  cosmology today. We propose to measure the extinction law, and its
  variation, directly through STIS FUV and NUV spectroscopy of 21 faint
  white dwarf stars, the Cosmic Flux Standards. These standards have
  SEDs that are exceptionally well-constrained by high S/N legacy HST
  panchromatic imaging, detailed ground-based optical spectroscopy, and
  temporal monitoring to assess variability. These Cosmic Flux Standards
  extend the CALSPEC system down to V~19.5 mag, and has been demonstrated
  that measurements of these standards will allow 1% absolute photometric
  calibration and 0.5% relative calibration, suitable for major upcoming
  projects such as the Vera Rubin Observatory and Nancy Grace Roman
  Space Telescope. These observations will allow a direct measurement
  of the extinction law by comparing the STIS spectrophotometry to the
  unreddened SEDs of the Cosmic Flux Standards, allowing a population
  inference of the extinction law, as well as line-of-sight estimates
  to each object. This probabilistic model of the extinction law will
  directly address dust as a source of systematic error, and the STIS
  FUV and NUV observations will also extend the validity of the standards
  to 1,150 Angstrom in preparation for future UV space-missions.

Title: An improved model for the spectra of discs of nova-like
    variables
Authors: Hubeny, Ivan; Long, Knox S.
Bibcode: 2021MNRAS.503.5534H
Altcode: 2021arXiv210309341H; 2021MNRAS.tmp..821H
  The spectra arising from the discs of nova-like variables show many of
  the features seen in stellar atmospheres. They are typically modelled
  either from an appropriated weighted set of stellar atmospheres or a
  disc atmosphere with energy is dissipated near the disc plane, with
  the effective temperature distribution expected from a steady-state
  accretion disc. However, these models generally overpredict the depth of
  the Balmer jump and the slope of the spectrum in the ultraviolet. The
  problem is likely due to energy dissipation in the disc atmosphere,
  which produces a flatter vertical temperature profile than is observed
  in stars. Here, we provide validation for this hypothesis in the
  form of spectra generated using the stellar atmosphere code TLUSTY
  using a parametric prescription for energy dissipation as a function
  of depth and closely match the spectrum of the nova-like IX Vel over
  the wavelength range 1150-6000 Å.

Title: TLUSTY and SYNSPEC Users's Guide IV: Upgraded Versions 208
    and 54
Authors: Hubeny, Ivan; Allende Prieto, Carlos; Osorio, Yeisson;
   Lanz, Thierry
Bibcode: 2021arXiv210402829H
Altcode:
  We present a brief description of the newly upgraded versions of the
  programs TLUSTY, version 208, and SYNSPEC, version 54. TLUSTY is used
  to generate model stellar atmospheres or accretion disks, and SYNSPEC
  produces detailed synthetic spectra and/or opacity tables. This paper
  complements published guides that provide a detailed description
  of earlier versions of the codes, TLUSTY205, and SYNSPEC51. The
  main upgrades include the flexible construction of opacity tables
  in SYNSPEC, and their use in producing hybrid models with TLUSTY},
  with important species treated in NLTE, while the bulk of opacity of
  atomic and molecular lines and continua are considered in LTE using
  a pre-calculated opacity table. There is also a number of additional
  changes and upgrades that increase the versatility and flexibility of
  these codes.

Title: Massive stars in the Small Magellanic Cloud. Evolution,
    rotation, and surface abundances
Authors: Bouret, J. -C.; Martins, F.; Hillier, D. J.; Marcolino,
   W. L. F.; Rocha-Pinto, H. J.; Georgy, C.; Lanz, T.; Hubeny, I.
Bibcode: 2021A&A...647A.134B
Altcode: 2021arXiv210109269B
  Context. The evolution of massive stars depends on several physical
  processes and parameters. Metallicity and rotation are among the most
  important, but their quantitative effects are not well understood. <BR
  /> Aims: To complement our earlier study on main-sequence stars,
  we study the evolutionary and physical properties of evolved O stars
  in the Small Magellanic Cloud (SMC). We focus in particular on their
  surface abundances to further investigate the efficiency of rotational
  mixing as a function of age, rotation, and global metallicity. <BR />
  Methods: We analysed the UV and optical spectra of 13 SMC O-type giants
  and supergiants using the stellar atmosphere code CMFGEN to derive
  photospheric and wind properties. We compared the inferred properties to
  theoretical predictions from evolution models. For a more comprehensive
  analysis, we interpret the results together with those we previously
  obtained for O-type dwarfs. <BR /> Results: Most dwarfs of our sample
  lie in the early phases of the main sequence. For a given initial mass,
  giants are farther along the evolutionary tracks, which confirms that
  they are indeed more evolved than dwarfs. Supergiants have higher
  initial masses and are located past the terminal-age main-sequence in
  each diagram. We find no clear trend of a mass discrepancy, regardless
  of the diagram that was used to estimate the evolutionary mass. Surface
  CNO abundances are consistent with nucleosynthesis from the CNO
  cycle. Comparisons to theoretical predictions reveal that the initial
  mixture is important when the observed trends in the N/C versus N/O
  diagram are to be reproduced. A trend for stronger chemical evolution
  for more evolved objects is observed. Above about 30 M<SUB>⊙</SUB>,
  more massive stars are on average more chemically enriched at a given
  evolutionary phase. Below 30 M<SUB>⊙</SUB>, the trend vanishes. This
  is qualitatively consistent with evolutionary models. A principal
  component analysis of the abundance ratios for the whole (dwarfs and
  evolved stars) sample supports the theoretical prediction that massive
  stars at low metallicity are more chemically processed than their
  Galactic counterparts. Finally, models including rotation generally
  reproduce the surface abundances and rotation rates when different
  initial rotational velocities are considered. Nevertheless, for some
  objects, a stronger braking and/or more efficient mixing is required. <P
  />This research is based on observations made with the NASA/ESA Hubble
  Space Telescope obtained from the Space Telescope Science Institute,
  which is operated by the Association of Universities for Research in
  Astronomy, Inc., under NASA contract NAS 5-26555. These observations
  are associated with programmes GO 7437, GO 9434, and GO 11625. <P
  />Based on data products from observations made with ESO Telescopes
  at the La Silla Paranal Observatory under programmes ID 67.D-0238,
  70.D-0164, 074.D-0109, 079.D-0073, and 079.D-0562.

Title: All-Order Full-Coulomb Quantum Spectral Line Shape Calculations
Authors: Gomez, Thomas; Nagayama, Taisuke; Cho, Patricia; Zammit,
   Mark; Fontes, Chris; Kilcrease, David; Bray, Igor; Hubeny, Ivan;
   Dunlap, Bart; Montgomery, Michael; Winget, Don
Bibcode: 2021APS..DPPPO3009G
Altcode:
  Understanding how atoms interact with hot dense matter (HDM) is
  essential for astrophysical and laboratory plasmas modeling and
  analysis. In high density plasmas, spectral lines are significantly
  pressure broadened. Line shape calculations and measurements thus
  provide a rare window that lets us examine how atoms interact in dense
  plasmas, for example inside stars. Up to now, spectral line-shape
  theories employed at least one of the following approximations:
  dipole, 2<SUP>nd</SUP>-order perturbation, and semi-classical. Here,
  we remove all three approximations simultaneously for the first time
  and test the importance for two applications: neutral hydrogen and
  highly-ionized magnesium. We found 15-50% change in the spectral line
  widths. We will discuss potential impact on white-dwarf spectroscopy,
  and plasma diagnostics. <P />SNL is managed and operated by NTESS
  under DOE NNSA contract DE-NA0003525.

Title: Mass-Metallicity Trends in Transiting Exoplanets from
    Atmospheric Abundances of H2O, Na, and K
Authors: Welbanks, Luis; Madhusudhan, Nikku; Allard, Nicole F.;
   Hubeny, Ivan; Spiegelman, Fernand; Leininger, Thierry
Bibcode: 2020EPSC...14..168W
Altcode:
  Atmospheric compositions can provide powerful diagnostics of formation
  and migration histories of planetary systems. In this talk, I will
  present the results of our latest survey of atmospheric compositions
  focused on atmospheric abundances of H2O, Na, and K. We employ a sample
  of 19 exoplanets spanning from cool mini-Neptunes to hot Jupiters,
  with equilibrium temperatures between ~300 and 2700 K. We employ the
  latest transmission spectra, new H2 broadened opacities of Na and K,
  and homogeneous Bayesian retrievals. We confirm detections of H2O in 14
  planets and detections of Na and K in 6 planets each. Among our sample,
  we find a mass-metallicity trend of increasing H2O abundances with
  decreasing mass, spanning generally substellar values for gas giants
  and stellar/superstellar for Neptunes and mini-Neptunes. However,
  the overall trend in H2O abundances, is significantly lower than
  the mass-metallicity relation for carbon in the solar system giant
  planets and similar predictions for exoplanets. On the other hand, the
  Na and K abundances for the gas giants are stellar or superstellar,
  consistent with each other, and generally consistent with the solar
  system metallicity trend. The H2O abundances in hot gas giants are
  likely due to low oxygen abundances relative to other elements rather
  than low overall metallicities, and provide new constraints on their
  formation mechanisms. Our results show that the differing trends in
  the abundances of species argue against the use of chemical equilibrium
  models with metallicity as one free parameter in atmospheric retrievals,
  as different elements can be differently enhanced.

Title: VizieR Online Data Catalog: Candidate spectrophotometric
    standard DA WDs (Calamida+, 2019)
Authors: Calamida, A.; Matheson, T.; Saha, A.; Olszewski, E.; Narayan,
   G.; Claver, J.; Shanahan, C.; Holberg, J.; Axelrod, T.; Bohlin, R.;
   Stubbs, C. W.; Deustua, S.; Hubeny, I.; MacKenty, J.; Points, S.;
   Rest, A.; Sabbi, E.
Bibcode: 2020yCat..18720199C
Altcode:
  Photometric data discussed in this investigation were collected with
  the WFC3 UVIS and IR cameras on board the HST during Cycle 20 and 22
  (proposals GO-12967 and GO-13711, PI: Saha). Observations were taken in
  five filters in Cycle 20, namely F336W, F475W, F625W, F775W, F160W. In
  Cycle 22 the near-UV filter F275W was added. Nine of the candidate
  DA white dwarfs (DAWDs) are distributed along the celestial equator
  and were observed in both Cycle 20 and Cycle 22, while the other 14
  DAWDs and the three HST primary CALSPEC standards were observed only
  in Cycle 22. Table 4 lists the log of the observations for Cycle 20
  and 22. Observations span a time interval of about 1yr for Cycle 20
  (2012 November until 2013 September) and about 1.3yr for Cycle 22
  (2014 September until 2016 January). The final magnitudes for the 23
  candidate spectrophotometric standard DAWDs and the HST primary CALSPEC
  WDs are listed in Table 9. <P />We used two different facilities to
  obtain spectra of our standard star candidates. As part of the HST
  photometry proposal, we were awarded Gemini/GMOS time. This amounted
  to 43hr from Cycle 20 (split over Gemini semesters 2013A and 2013B) and
  28.1hr from Cycle 22 (split over Gemini semesters 2015A and 2015B). The
  final spectra are continuous from 3500 to 6360Å. Alternate spectra were
  obtained in 2015 at the Multiple Mirror Telescope (MMT) with the Blue
  Channel spectrograph (wavelength coverage from 3400 to 8400Å). Details
  of the observations with both facilities are presented in Table 5. <P
  />(6 data files).

Title: New Grids of Pure-hydrogen White Dwarf NLTE Model Atmospheres
    and the HST/STIS Flux Calibration
Authors: Bohlin, Ralph C.; Hubeny, Ivan; Rauch, Thomas
Bibcode: 2020AJ....160...21B
Altcode: 2020arXiv200510945B
  Nonlocal thermodynamic equilibrium (NLTE) calculations of hot white
  dwarf (WD) model atmospheres are the cornerstone of modern flux
  calibrations for the Hubble Space Telescope and for the CALSPEC
  database. These theoretical spectral energy distributions (SEDs)
  provide the relative flux versus wavelength, and only the absolute
  flux level remains to be set by reconciling the measured absolute flux
  of Vega in the visible with the Midcourse Space Experiment values for
  Sirius in the mid-IR. The most recent SEDs calculated by the TLUSTY
  and TMAP NLTE model atmosphere codes for the primary WDs G191-B2B,
  GD 153, and GD 71 show improved agreement to 1% from 1500 Å to 30
  μm, in comparison to the previous 1% consistency only from 2000 Å
  to 5 μm. These new NLTE models of hot WDs now provide consistent flux
  standards from the far UV to the mid-IR.

Title: H-He collision-induced satellite in the Lyman α profile of
    DBA white dwarf stars
Authors: Allard, Nicole F.; Kielkopf, John F.; Xu, Siyi; Guillon,
   Grégoire; Mehnen, Bilel; Linguerri, Roberto; Al Mogren, Muneerah
   Mogren; Hochlaf, Majdi; Hubeny, Ivan
Bibcode: 2020MNRAS.494..868A
Altcode: 2020arXiv200305110A; 2020MNRAS.tmp..656A
  The spectra of helium-dominated white dwarf stars with hydrogen in
  their atmosphere present a distinctive broad feature centred around 1160
  Å in the blue wing of the Lyman α line. It is extremely apparent in
  WD 1425+540 recently observed with Hubble Space Telescope(HST) Cosmic
  Origins Spectrograph (COS). With new theoretical line profiles based on
  ab initio atomic interaction potentials we show that this feature is
  a signature of a collision-induced satellite due to an asymptotically
  forbidden transition. This quasi-molecular spectral satellite is
  crucial to understanding the asymmetrical shape of Lyman α seen
  in this and other white dwarf spectra. Our previous work predicting
  this absorption feature was limited by molecular potentials that were
  not adequate to follow the atomic interactions with spectroscopic
  precision to the asymptotic limit of large separation. A new set of
  potential energy curves and electronic dipole transition moments for
  the lowest electronic states of the H-He system were developed to
  account accurately for the behaviour of the atomic interactions at
  all distances, from the chemical regime within 1 Å out to where
  the radiating H atoms are not significantly perturbed by their
  neighbours. We use a general unified theory of collision-broadened
  atomic spectral lines to describe a rigorous treatment of hydrogen
  Lyman α with these potentials and present a new study of its broadening
  by radiative collisions of hydrogen and neutral helium. These results
  enable ab initio modelling of radiative transport in DBA white dwarf
  atmospheres.

Title: NLTE for APOGEE: simultaneous multi-element NLTE radiative
    transfer
Authors: Osorio, Y.; Allende Prieto, C.; Hubeny, I.; Mészáros, Sz.;
   Shetrone, M.
Bibcode: 2020A&A...637A..80O
Altcode: 2020arXiv200313353O
  Context. Relaxing the assumption of local thermodynamic equilibrium
  (LTE) in modelling stellar spectra is a necessary step to determine
  chemical abundances to better than about 10% in late-type stars. <BR />
  Aims: We describe our multi-element (Na, Mg, K, and Ca) non-LTE (NLTE)
  calculations, which can be applied to the APOGEE survey. <BR /> Methods:
  The new version of TLUSTY allows for the calculation of restricted
  NLTE in cool stars using pre-calculated opacity tables. We demonstrate
  that TLUSTY gives consistent results with MULTI, a well-tested code
  for NLTE in cool stars. We used TLUSTY to perform LTE and a series
  of NLTE calculations that simultaneously used all combinations of
  one, two, three and four of the elements in NLTE. <BR /> Results: We
  take into account that departures from LTE in one element can affect
  others through changes in the opacities of Na, Mg, K, and Ca. We
  find that atomic Mg, which provides strong UV opacity and exhibits
  significant departures from LTE in the low-energy states, can affect
  the NLTE populations of Ca, leading to abundance corrections as large
  as 0.07 dex. The differences in the derived abundances between the
  single-element and the multi-element cases can exceed those between the
  single-element NLTE determinations and an LTE analysis. We therefore
  caution that this is not always a second-order effect. Based on
  detailed tests for three stars with reliable atmospheric parameters
  (Arcturus, Procyon, and the Sun), we conclude that our NLTE calculations
  provide abundance corrections that can in the optical amount to 0.1,
  0.2, and 0.7 dex for Ca, Na and K, but LTE is a good approximation
  for Mg. In the H-band, NLTE corrections are much smaller and always
  lower than 0.1 dex. The derived NLTE abundances in the optical and
  in the IR are consistent. In all three stars, NLTE line profiles
  fit the observations better than the LTE counterparts for all four
  elements. <BR /> Conclusions: The atomic elements in ionisation stages
  where over-ionisation is an important NLTE mechanism are likely affected
  by departures from LTE in Mg. Particular care must be taken with the
  collisions that are adopted for high-lying levels when NLTE profiles
  of lines in the H-band are calculated. The derived NLTE corrections in
  the optical and in the H-band differ, but the derived NLTE abundances
  are consistent between the two spectral regions.

Title: Supernovae Chemical Yields in Magellanic Cloud Environments
Authors: Peters, G. J.; Lanz, T.; Bouret, J.; Proffitt, C. R.; Adelman,
   S. J.; Hubeny, I.
Bibcode: 2020AAS...23511025P
Altcode:
  Recently there has been interest in the abundance of Mn and other
  Fe group elements as diagnostics for determining the progenitors of
  SNe Ia and their role in the chemical evolution of a galaxy. We have
  combined recent spectroscopic observations from the Cosmic Origins
  Spectrograph (COS) on the Hubble Space Telescope with archival data from
  the Far Ultraviolet Spectroscopic Explorer (FUSE) and ESO's VLT/UVES to
  determine the abundances of the Fe group elements (Ti, V, Cr, Mn, Fe,
  Co, &amp; Ni) in main sequence B stars in the Magellanic Clouds. Here we
  report results for NGC 1818-D1 (LMC) and AV 304 (SMC). The analysis was
  carried through using the Hubeny/Lanz NLTE programs TLUSTY/SYNSPEC. The
  COS observations were secured with the G130M, G160M, G185M, and G225M
  gratings. Combined with the FUSE data, we have achieved spectral
  coverage in the UV from 950 to 2400 A. Measurable lines from the Fe
  group, except for a very few multiplets of Fe II, III are not found
  in optical spectra. The following stellar parameters were adopted:
  T<SUB>eff</SUB> = 24700 K, log g = 4.0 cm/s<SUP>2</SUP>, Vturb =
  0 km/s, and v sin i = 30 km/s for NGC 1818-D1, and T<SUB>eff</SUB> =
  27500 K, log g = 3.7 cm/s<SUP>2</SUP>, Vturb = 1 km/s, and v sin i =
  8 km/s for AV 304. Both stars show Fe group abundances about 0.2-0.3
  dex smaller than their lighter elements when compared to solar values
  and the LMC/SMC averages. However Ti, an alpha-process element, appears
  to have an abundance more in line with LMC/SMC values. [Mn/Fe] ranges
  from 0.2 dex (NGC 1818-D1) to 0.1 dex (AV 304) with an uncertainty of
  0.2 dex, and implies that the progenitors that produced their Fe group
  material probably had Chandrasekhar masses (cf. Seitenzahl et al. 2013,
  A&amp;A, 559, L5). Support from STScI grants HST-GO-14081.002 and
  HST-GO-13346.022, and USC's Women in Science and Engineering (WiSE)
  program are greatly appreciated.

Title: Mass-Metallicity Trends in Transiting Exoplanets from
    Atmospheric Abundances of H<SUB>2</SUB>O, Na, and K
Authors: Welbanks, Luis; Madhusudhan, Nikku; Allard, Nicole F.;
   Hubeny, Ivan; Spiegelman, Fernand; Leininger, Thierry
Bibcode: 2019ApJ...887L..20W
Altcode: 2019arXiv191204904W
  Atmospheric compositions can provide powerful diagnostics of formation
  and migration histories of planetary systems. We investigate constraints
  on atmospheric abundances of H<SUB>2</SUB>O, Na, and K, in a sample
  of transiting exoplanets using the latest transmission spectra and
  new H<SUB>2</SUB> broadened opacities of Na and K. Our sample of
  19 exoplanets spans from cool mini-Neptunes to hot Jupiters, with
  equilibrium temperatures between ∼300 and 2700 K. Using homogeneous
  Bayesian retrievals we report atmospheric abundances of Na, K, and
  H<SUB>2</SUB>O, and their detection significances, confirming 6 planets
  with strong Na detections, 6 with K, and 14 with H<SUB>2</SUB>O. We find
  a mass-metallicity trend of increasing H<SUB>2</SUB>O abundances with
  decreasing mass, spanning generally substellar values for gas giants
  and stellar/superstellar for Neptunes and mini-Neptunes. However,
  the overall trend in H<SUB>2</SUB>O abundances, from mini-Neptunes
  to hot Jupiters, is significantly lower than the mass-metallicity
  relation for carbon in the solar system giant planets and similar
  predictions for exoplanets. On the other hand, the Na and K abundances
  for the gas giants are stellar or superstellar, consistent with each
  other, and generally consistent with the solar system metallicity
  trend. The H<SUB>2</SUB>O abundances in hot gas giants are likely due
  to low oxygen abundances relative to other elements rather than low
  overall metallicities, and provide new constraints on their formation
  mechanisms. The differing trends in the abundances of species argue
  against the use of chemical equilibrium models with metallicity as
  one free parameter in atmospheric retrievals, as different elements
  can be differently enhanced.

Title: New insight on accretion shocks onto young stellar
    objects. Chromospheric feedback and radiation transfer
Authors: de Sá, L.; Chièze, J. -P.; Stehlé, C.; Hubeny, I.; Lanz,
   T.; Cayatte, V.
Bibcode: 2019A&A...630A..84D
Altcode:
  Context. Material accreted onto classical T Tauri stars is expected
  to form a hot quasi-periodic plasma structure that radiates
  in X-rays. Simulations of this phenomenon only partly match
  observations. They all rely on a static model for the chromosphere
  and on the assumption that radiation and matter are decoupled. <BR />
  Aims: We explore the effects of a shock-heated chromosphere and of
  the coupling between radiation and hydrodynamics on the structure
  and dynamics of the accretion flow. <BR /> Methods: We simulated
  accretion columns that fall onto a stellar chromosphere using the
  1D ALE code AstroLabE. This code solves the hydrodynamics equations
  along with the first two moment equations for radiation transfer,
  with the help of a dedicated opacity table for the coupling between
  matter and radiation. We derive the total electron and ion densities
  from collisional-radiative model. <BR /> Results: The chromospheric
  acoustic heating affects the duration of the cycle and the structure
  of the heated slab. In addition, the coupling between radiation
  and hydrodynamics leads to a heating of the accretion flow and of
  the chromosphere: the whole column is pushed up by the inflating
  chromosphere over several times the steady chromosphere thickness. These
  last two conclusions are in agreement with the computed monochromatic
  intensity. Acoustic heating and radiation coupling affect the amplitude
  and temporal variations of the net X-ray luminosity, which varies
  between 30 and 94% of the incoming mechanical energy flux, depending
  on which model is considered.

Title: Stars and Stellar Black Holes in the Low-metallicity Galaxy
    I Zw 18
Authors: Heap, S. R.; Hubeny, I.; Lanz, T. M.
Bibcode: 2019ASPC..519..267H
Altcode:
  I Zw 18 is a star-forming dwarf galaxy having a very low metal content,
  O/H ∼ 1/50 solar (Skillman &amp; Kennicutt 1993). While galaxies
  with such low metallicity are rare in the low-redshift universe,
  they are likely to be common in galaxies at cosmic dawn. Thus,
  I Zw 18 is a “living” template for z &gt; 6 galaxies. We have
  obtained HST/COS far-UV spectra of the northwest star cluster in I
  Zw 18 and have compared them to SYNSPEC model spectra by Lanz &amp;
  Hubeny (2003, 2007) in order to determine the properties of the stellar
  population. We have also compared the observed spectra of I Zw 18-NW to
  the CLOUDSPEC models (Hubeny et al. 2000) of the stellar cluster with
  an embedded ultra-luminous X-ray source (ULX). This comparison reveals
  feedback of the stellar black hole in the form of photoionization and
  heating. Such models can be used as starting points to explore the
  physical conditions in which stars and black holes form and evolve in
  an extremely low-metallicity environment at high redshift.

Title: The Radial Oxygen Abundance Gradient from OB Stars in the
    Outer Galactic Disk
Authors: Daflon, Simone; Bragança, Gustavo A.; Lanz, Thierry; Cunha,
   Katia; Hubeny, Ivan; Bensby, Thomas; McMillan, Paul J.; Garmany,
   Kate; Glaspey, John W.; Borges Fernandes, Marcelo; Oey, Sally
Bibcode: 2019ASPC..519..213D
Altcode:
  Metallicity gradients are important constraints for models of chemical
  evolution of the Galaxy. We present the current radial gradient of
  oxygen abundances using a sample of main-sequence OB stars located
  in the outer Galactic Disk, considering non-NLTE abundances, and
  distances based on GAIA DR2 results. We compare the obtained gradient
  with results from other young objects of the Galactic Disk.

Title: 3D Spectral Radiative Transfer and Perspectives for
    Spectroscopic Diagnostics
Authors: Ibgui, Laurent; Hubeny, Ivan; Lanz, Thierry; González,
   Matthias; Stehlé, Chantal; Orlando, Salvatore; Colombo, Salvatore
Bibcode: 2019ASPC..519...21I
Altcode:
  We present the features of the three-dimensional (3D) radiative
  transfer code IRIS, which synthesizes spectra emitted from hydrodynamics
  structures. We discuss our first application of IRIS to the analysis
  of a laboratory radiative shock. We demonstrate, with the help
  of the radiation hydrodynamics (RHD) code HERACLES, the existence
  of a radiative precursor. We validate the gray approximated model
  M<SUB>1</SUB> used by HERACLES. We show a couple of synthesized X-UV
  spectra of such a shock. We finally open up our discussion to the future
  possibilities of spectroscopic diagnostics of accreting streams onto
  the surface of Classical T Tauri stars (CTTSs).

Title: Radiation Transport in Astronomical Objects: Yesterday, Today,
    and Tomorrow
Authors: Hubeny, Ivan
Bibcode: 2019ASPC..519...75H
Altcode:
  First, I present a briefly description of some highlights of research
  that my collaborators and I achieved in the field of astrophysical
  radiative transfer and its application to modeling stellar and
  planetary atmospheres and accretion disks. On the application side,
  an emphasis is given to the computer programs TLUSTY for computing
  model stellar atmospheres and disks, COOLTLUSTY, its variant for
  modeling atmospheres of giant planets and brown dwarfs, and SYNSPEC,
  a general spectrum synthesis program. Then, I briefly summarize the
  present state and current upgrades of these codes. Finally, I outline
  several general topics that I think will be pursued in the near future,
  such as 3-D radiation hydrodynamic description of atmospheres and disks,
  and complex non-equilibrium models of exoplanetary atmospheres.

Title: Radiation Feedback in Accretion Shocks on Young Stars
Authors: de Sá, Lionel; Stehlé, Chantal; Chièze, Jean-Pierre;
   Hubeny, Ivan; Lanz, Thierry; Colombo, Salvatore; Cayatte, Véronique;
   Ibgui, Laurent; Orlando, Salvatore
Bibcode: 2019ASPC..519..281D
Altcode:
  The first stages of pre-main sequence stars evolution are governed
  by exchanges of mass and momentum between the proto-star and its
  accretion disk. These quantities remain uncertain due to numerous
  unanswered questions concerning the topology of the accretion flow,
  its temperature, and its dynamics. In this work, we first present 1D
  simulations of accretion columns falling onto a a stellar chromosphere;
  the goal is to inspect the feedback of the dynamics of the chromosphere
  on the accretion flow. Then, we analyze the effect of radiation
  absorption and emission on the flow. The simulations take benefit of
  a newly generated base of opacities computed by SYNSPEC code for the
  conditions of the present astrophysical process. We finally present
  our perspectives on this topic.

Title: Radial abundance gradients in the outer Galactic disk as
    traced by main-sequence OB stars
Authors: Bragança, G. A.; Daflon, S.; Lanz, T.; Cunha, K.; Bensby,
   T.; McMillan, P. J.; Garmany, C. D.; Glaspey, J. W.; Borges Fernandes,
   M.; Oey, M. S.; Hubeny, I.
Bibcode: 2019A&A...625A.120B
Altcode: 2019arXiv190404340B
  Context. Elemental abundance gradients in galactic disks are important
  constraints for models of how spiral galaxies form and evolve. However,
  the abundance structure of the outer disk region of the Milky Way
  is poorly known, which hampers our understanding of the spiral
  galaxy that is closest to us and that can be studied in greatest
  detail. Young OB stars are good tracers of the present-day chemical
  abundance distribution of a stellar population and because of their
  high luminosities they can easily be observed at large distances,
  making them suitable to explore and map the abundance structure and
  gradients in the outer regions of the Galactic disk. <BR /> Aims: Using
  a sample of 31 main-sequence OB stars located between galactocentric
  distances 8.4-15.6 kpc, we aim to probe the present-day radial abundance
  gradients of the Galactic disk. <BR /> Methods: The analysis is
  based on high-resolution spectra obtained with the MIKE spectrograph
  on the Magellan Clay 6.5-m telescope on Las Campanas. We used a
  non-NLTE analysis in a self-consistent semi-automatic routine based
  on TLUSTY and SYNSPEC to determine atmospheric parameters and chemical
  abundances. <BR /> Results: Stellar parameters (effective temperature,
  surface gravity, projected rotational velocity, microturbulence, and
  macroturbulence) and silicon and oxygen abundances are presented for 28
  stars located beyond 9 kpc from the Galactic center plus three stars
  in the solar neighborhood. The stars of our sample are mostly on the
  main-sequence, with effective temperatures between 20 800-31 300 K,
  and surface gravities between 3.23-4.45 dex. The radial oxygen and
  silicon abundance gradients are negative and have slopes of -0.07
  dex kpc<SUP>-1</SUP> and -0.09 dex kpc<SUP>-1</SUP>, respectively,
  in the region 8.4 ≤ R<SUB>G</SUB> ≤ 15.6 kpc. <BR /> Conclusions:
  The obtained gradients are compatible with the present-day oxygen and
  silicon abundances measured in the solar neighborhood and are consistent
  with radial metallicity gradients predicted by chemodynamical models
  of Galaxy Evolution for a subsample of young stars located close to
  the Galactic plane. <P />Based on data obtained with the Magellan Clay
  telescope at the Las Campanas observatory and the ESO/MPI telescope
  at La Silla under the ESO-ON agreement.

Title: Subpercent Photometry: Faint DA White Dwarf Spectrophotometric
    Standards for Astrophysical Observatories
Authors: Narayan, Gautham; Matheson, Thomas; Saha, Abhijit; Axelrod,
   Tim; Calamida, Annalisa; Olszewski, Edward; Claver, Jenna; Mandel,
   Kaisey S.; Bohlin, Ralph C.; Holberg, Jay B.; Deustua, Susana; Rest,
   Armin; Stubbs, Christopher W.; Shanahan, Clare E.; Vaz, Amali L.;
   Zenteno, Alfredo; Strampelli, Giovanni; Hubeny, Ivan; Points, Sean;
   Sabbi, Elena; Mackenty, John
Bibcode: 2019ApJS..241...20N
Altcode: 2018arXiv181112534N
  We have established a network of 19 faint (16.5 mag &lt; V &lt; 19 mag)
  northern and equatorial DA white dwarfs (WDs) as spectrophotometric
  standards for present and future wide-field observatories. Our analysis
  infers spectral energy distribution (SED) models for the stars that
  are tied to the three CALSPEC primary standards. Our SED models are
  consistent with panchromatic Hubble Space Telescope photometry to
  better than 1%. The excellent agreement between observations and
  models validates the use of non-LTE DA WD atmospheres extinguished
  by interstellar dust as accurate spectrophotometric references. Our
  standards are accessible from both hemispheres and suitable for
  ground- and space-based observatories covering the ultraviolet to the
  near-infrared. The high precision of these faint sources makes our
  network of standards ideally suited for any experiment that has very
  stringent requirements on flux calibration, such as studies of dark
  energy using the Large Synoptic Survey Telescope and the Wide-field
  Infrared Survey Telescope.

Title: New insight on Young Stellar Objects accretion shocks --
    a claim for NLTE opacities
Authors: de Sá, Lionel; Chièze, Jean-Pierre; Stehlé, Chantal;
   Hubeny, Ivan; Lanz, Thierry; Cayatte, Véronique
Bibcode: 2019arXiv190409156D
Altcode:
  Context. Accreted material onto CTTSs is expected to form a hot
  quasi-periodic plasma structure that radiates in X-rays. Simulations
  of this phenomenon only partly match with observations. They all rely
  on a static model for the chromosphere model and on the assumption
  that radiation and matter are decoupled. Aims. We explore the effects
  on the structure and on the dynamics of the accretion flow of both a
  shock-heated chromosphere and of the coupling between radiation and
  hydrodynamics. Methods. We simulate accretion columns falling onto
  a stellar chromosphere using the 1D ALE code AstroLabE. This code
  solves the hydrodynamics equations along with the two first momenta
  equations for radiation transfer, with the help of a dedicated opacity
  table for the coupling between matter and radiation. We derive the
  total electron and ions densities from collisional-radiative NLTE
  ionisation equilibrium. Results. The chromospheric acoustic heating
  has an impact on the duration of the cycle and on the structure
  of the heated slab. In addition, the coupling between radiation
  and hydrodynamics leads to a heating of the accretion flow and the
  chromosphere, inducing a possible unburial of the whole column. These
  two last conclusions are in agreement with the computed monochromatic
  intensity. Both effects (acoustic heating and radiation coupling)
  have an influence on the amplitude and temporal variations of the
  net X-ray luminosity, which varies between 30 and 94% of the incoming
  mechanical energy flux, depending on the model considered.

Title: Photometry and Spectroscopy of Faint Candidate
    Spectrophotometric Standard DA White Dwarfs
Authors: Calamida, Annalisa; Matheson, Thomas; Saha, Abhijit;
   Olszewski, Edward; Narayan, Gautham; Claver, Jenna; Shanahan, Clare;
   Holberg, Jay; Axelrod, Tim; Bohlin, Ralph; Stubbs, Christopher W.;
   Deustua, Susana; Hubeny, Ivan; Mackenty, John; Points, Sean; Rest,
   Armin; Sabbi, Elena
Bibcode: 2019ApJ...872..199C
Altcode: 2018arXiv181200034C
  We present precise photometry and spectroscopy for 23 candidate
  spectrophotometric standard white dwarfs. The selected stars are
  distributed in the Northern hemisphere and around the celestial equator,
  and are all fainter than r ∼ 16.5 mag. This network of stars,
  when established as standards and together with the three Hubble
  Space Telescope primary CALSPEC white dwarfs, will provide a set of
  spectrophotometric standards to directly calibrate data products to
  better than 1%. In future deep photometric surveys and facilities,
  these new faint standard white dwarfs will have enough signal-to-noise
  ratio to be measured accurately while still avoiding saturation. They
  will also fall within the dynamic range of large telescopes and
  their instruments for the foreseeable future. This paper discusses
  the provenance of the observational data for our candidate standard
  stars. A comparison with models, reconciliation with reddening, and the
  consequent derivation of the full spectral energy density distributions
  for each of them is reserved for a subsequent paper.

Title: Modelling the Accretion on Young Stars, Recent Results and
    Perspectives
Authors: de Sá, L.; Stehlé, C.; Chièze, J. P.; Hubeny, I.; Lanz,
   T.; Colombo, S.; Ibgui, L.; Orlando, S.
Bibcode: 2019ASSP...55...29D
Altcode:
  No abstract at ADS

Title: A collection of model stellar spectra for spectral types B
    to early-M
Authors: Allende Prieto, C.; Koesterke, L.; Hubeny, I.; Bautista,
   M. A.; Barklem, P. S.; Nahar, S. N.
Bibcode: 2018A&A...618A..25A
Altcode: 2018arXiv180706049A
  Context. Models of stellar spectra are necessary for interpreting light
  from individual stars, planets, integrated stellar populations, nebulae,
  and the interstellar medium. <BR /> Aims: We provide a comprehensive
  and homogeneous collection of synthetic spectra for a wide range of
  atmospheric parameters and chemical compositions. <BR /> Methods:
  We compile atomic and molecular data from the literature. We adopt
  the largest and most recent set of ATLAS9 model atmospheres, and use
  the radiative code ASSɛT. <BR /> Results: The resulting collection
  of spectra is made publicly available at medium and high-resolution
  (R ≡ λ/δλ = 10 000, 100 000 and 300 000) spectral grids,
  which include variations in effective temperature between 3500 K
  and 30 000 K, surface gravity (0 ≤ log g ≤ 5), and metallicity
  (-5 ≤ [Fe/H] ≤ +0:5), spanning the wavelength interval 120-6500
  nm. A second set of denser grids with additional dimensions, [α/Fe]
  and micro-turbulence, are also provided (covering 200-2500 nm). We
  compare models with observations for a few representative cases. <P
  />Data files are only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/618/A25">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/618/A25</A>

Title: VizieR Online Data Catalog: Model stellar spectra for B to
    early-M (Allende Prieto+, 2018)
Authors: Allende Prieto, C.; Koesterke, L.; Hubeny, I.; Bautista,
   M.; Barklem, P. S.; Nahar, S. N.
Bibcode: 2018yCat..36180025A
Altcode:
  The following text describes the data files available from
  ftp://carlos:allende@ftp.ll.iac.es/collection <P />These are in ASCII
  (but bzip2 compressed), and ready to be used with the FERRE code
  (github.com/callendeprieto/ferre). The format includes a header
  and as many rows as model spectra. See the FERRE manual for more
  details (github.com/callendeprieto/ferre/docs/ferre.pdf). <P />There
  are two main families of files. The 'coarse' (nsc) grids consider
  three atmospheric parameters ([Fe/H], Teff and logg) and typically
  include hundreds of models on a very coarse network, while the
  'large' (ns) grids consider five (the previous three plus [alpha/Fe]
  and microturbulence), and include tens to hundreds of thousands of
  models. <P />The files are numbered 1-5 depending on the Teff range
  they span. There are files (ns and nsc) smoothed with a Gaussian
  kernal to R=10,000, while nsc files are provided for R=100,000
  and 200,000 as well. The spectral range is 0.12-6.6um for the nsc
  files and 0.2-2.5um for the ns files. <P />for the nsc files and
  0.2-2.5um for the ns files. <P />nsc ('coarse' grids): [Fe/H], Teff,
  logg <P />size filename Teff range R <P />158004765 f_nsc1.dat.bz2
  3500&lt;= Teff&lt;=6000 10000 128868874 f_nsc2.dat.bz2 5750&lt;=
  Teff&lt;=8000 102539424 f_nsc3.dat.bz2 7000&lt;= Teff&lt;=12000 77786534
  f_nsc4.dat.bz2 10000&lt;=Teff&lt;=20000 26089034 f_nsc5.dat.bz2
  20000&lt;=Teff&lt;=30000 <P />1430284037 f_hnsc1.dat.bz2 3500&lt;=
  Teff&lt;=6000 100000 1159906320 f_hnsc2.dat.bz2 5750&lt;= Teff&lt;=8000
  913976329 f_hnsc3.dat.bz2 7000&lt;= Teff&lt;=12000 695827559
  f_hnsc4.dat.bz2 10000&lt;=Teff&lt;=20000 234598400 f_hnsc5.dat.bz2
  20000&lt;=Teff&lt;=30000 <P />2596690648 f_uhnsc1.dat.bz2 3500&lt;=
  Teff&lt;=6000 300000 2067630039 f_uhnsc2.dat.bz2 5750&lt;= Teff&lt;=8000
  1605227763 f_uhnsc3.dat.bz2 7000&lt;= Teff&lt;=12000 1221970143
  f_uhnsc4.dat.bz2 10000&lt;=Teff&lt;=20000 411096450 f_uhnsc5.dat.bz2
  20000&lt;=Teff&lt;=30000 <P />ns ('large' grids): [Fe/H], [alpha/Fe],
  log(micro), Teff, logg <P />30936708717 f_ns1.dat.bz2 3500&lt;=
  Teff&lt;=6000 10000 22957349531 f_ns2.dat.bz2 5750&lt;= Teff&lt;=8000
  19640724566 f_ns3.dat.bz2 7000&lt;= Teff&lt;=12000 14267448478
  f_ns4.dat.bz2 10000&lt;=Teff&lt;=20000 8622793847 f_ns5.dat.bz2
  20000&lt;=Teff&lt;=30000 <P />(2 data files).

Title: The Abundances of the Fe Group Elements in AV 304, an Abundance
    Standard in the Small Magellanic Cloud
Authors: Peters, Geraldine J.; Lanz, Thierry; Bouret, Jean-Claude;
   Proffitt, Charles R.; Adelman, Saul J.; Hubeny, Ivan
Bibcode: 2018AAS...23231704P
Altcode:
  AV 304 is a B0.5 IV field star in the Small Magellanic Cloud with
  ultra-sharp spectral lines that has emerged as an abundance standard. We
  have combined recent spectroscopic observations from the Cosmic Origins
  Spectrograph (COS) on the Hubble Space Telescope with archival data from
  the Far Ultraviolet Spectroscopic Explorer (FUSE) and ESO’s VLT/UVES
  to determine the abundances of the Fe group elements (Ti, V, Cr, Mn, Fe,
  Co, &amp; Ni). The analysis was carried through using the Hubeny/Lanz
  NLTE programs TLUSTY/SYNSPEC. The COS observations were secured with the
  G130M, G160M, G185M, and G225M gratings. Combined with the FUSE data, we
  have achieved spectral coverage in the UV from 950 to 2400 A. Measurable
  lines from the Fe group, except for a very few multiplets of Fe II, III
  are not observed in optical spectra. The following stellar parameters
  were found: Teff = 27500±500 K, log g = 3.7±0.1 cm/s<SUP>2</SUP>,
  Vturb= 1±1 km/s, and v sin i = 8 ±2 km/s. The Fe abundance appears
  to be only slightly lower than the mean depletion in the SMC, but the
  other Fe group elements are underabundant by 0.3 dex or more. This study
  confirmed the low abundance of nitrogen (-1.25 dex relative to the solar
  value) that was reported by Peters &amp; Adelman (ASP Conf. Series, 348,
  p. 136, 2006). Whereas the light elements are delivered to the ISM by
  core-collapse supernovae (CCSNe), the Fe group elements are believed
  to come mostly from low/intermediate mass binaries containing white
  dwarfs that undergo SNe Ia explosions. A single SNe Ia can deliver
  0.5 solar masses of pure Fe (and maybe Mn) to the ISM compared with
  about 0.07 solar masses from a CCSNe. It appears that there is very
  little processed material from its interior in the atmosphere of AV
  304 and that the star did not form from an interstellar cloud that
  was enriched by material from earlier supernova activity. Support from
  STScI grants HST-GO-14081.002 and HST-GO-13346.022, and USC’s Women
  in Science and Engineering (WiSE) program is greatly appreciated.

Title: Sub-percent Photometry: Faint DA White Dwarf Spectrophotometric
    Standards for Astrophysical Observatories
Authors: Narayan, Gautham; Axelrod, Tim; Calamida, Annalisa; Saha,
   Abhijit; Matheson, Thomas; Olszewski, Edward; Holberg, Jay; Holberg,
   Jay; Bohlin, Ralph; Stubbs, Christopher W.; Rest, Armin; Deustua,
   Susana; Sabbi, Elena; MacKenty, John W.; Points, Sean D.; Hubeny, Ivan
Bibcode: 2018AAS...23135417N
Altcode:
  We have established a network of faint (16.5 &lt; V &lt; 19) hot DA
  white dwarfs as spectrophotometric standards for present and future
  wide-field observatories. Our standards are accessible from both
  hemispheres and suitable for ground and space-based covering the
  UV to the near IR. The network is tied directly to the most precise
  astrophysical reference presently available - the CALSPEC standards -
  through a multi-cycle program imaging using the Wide-Field Camera 3
  (WFC3) on the Hubble Space Telescope (HST). We have developed two
  independent analyses to forward model all the observed photometry and
  ground-based spectroscopy and infer a spectral energy distribution
  for each source using a non-local-thermodynamic-equilibrium (NLTE)
  DA white dwarf atmosphere extincted by interstellar dust. The
  models are in excellent agreement with each other, and agree with the
  observations to better than 0.01 mag in all passbands, and better than
  0.005 mag in the optical. The high-precision of these faint sources,
  tied directly to the most accurate flux standards presently available,
  make our network of standards ideally suited for any experiments that
  have very stringent requirements on absolute flux calibration, such
  as studies of dark energy using the Large Synoptic Survey Telescope
  (LSST) and the Wide-Field Infrared Survey Telescope (WFIRST).

Title: Modelling ultraviolet-line diagnostics of stars, the ionized
    and the neutral interstellar medium in star-forming galaxies
Authors: Vidal-García, A.; Charlot, S.; Bruzual, G.; Hubeny, I.
Bibcode: 2017MNRAS.470.3532V
Altcode: 2017arXiv170510320V
  We combine state-of-the-art models for the production of stellar
  radiation and its transfer through the interstellar medium (ISM) to
  investigate ultraviolet-line diagnostics of stars, the ionized and
  the neutral ISM in star-forming galaxies. We start by assessing the
  reliability of our stellar population synthesis modelling by fitting
  absorption-line indices in the ISM-free ultraviolet spectra of 10
  Large Magellanic Cloud clusters. In doing so, we find that neglecting
  stochastic sampling of the stellar initial mass function in these young
  (∼10-100 Myr), low-mass clusters affects negligibly ultraviolet-based
  age and metallicity estimates but can lead to significant overestimates
  of stellar mass. Then, we proceed and develop a simple approach,
  based on an idealized description of the main features of the ISM,
  to compute in a physically consistent way the combined influence of
  nebular emission and interstellar absorption on ultraviolet spectra
  of star-forming galaxies. Our model accounts for the transfer of
  radiation through the ionized interiors and outer neutral envelopes of
  short-lived stellar birth clouds, as well as for radiative transfer
  through a diffuse intercloud medium. We use this approach to explore
  the entangled signatures of stars, the ionized and the neutral ISM in
  ultraviolet spectra of star-forming galaxies. We find that, aside from
  a few notable exceptions, most standard ultraviolet indices defined in
  the spectra of ISM-free stellar populations are prone to significant
  contamination by the ISM, which increases with metallicity. We also
  identify several nebular-emission and interstellar-absorption features,
  which stand out as particularly clean tracers of the different phases
  of the ISM.

Title: Model atmospheres of sub-stellar mass objects
Authors: Hubeny, Ivan
Bibcode: 2017MNRAS.469..841H
Altcode: 2017arXiv170309283H
  We present an outline of basic assumptions and governing structural
  equations describing atmospheres of sub-stellar mass objects, in
  particular the extrasolar giant planets and brown dwarfs. Although most
  of the presentation of the physical and numerical background is generic,
  details of the implementation pertain mostly to the code cooltlusty. We
  also present a review of numerical approaches and computer codes devised
  to solve the structural equations, and make a critical evaluation of
  their efficiency and accuracy.

Title: The Validity of 21 cm Spin Temperature as a Kinetic Temperature
    Indicator in Atomic and Molecular Gas
Authors: Shaw, Gargi; Ferland, G. J.; Hubeny, I.
Bibcode: 2017ApJ...843..149S
Altcode: 2017arXiv170601425S
  The gas kinetic temperature (T <SUB> K </SUB>) of various interstellar
  environments is often inferred from observations that can deduce
  level populations of atoms, ions, or molecules using spectral
  line observations; H I 21 cm is perhaps the most widely used,
  and has a long history. Usually the H I 21 cm line is assumed
  to be in thermal equilibrium and the populations are given by the
  Boltzmann distribution. A variety of processes, many involving Lyα,
  can affect the 21 cm line. Here we show how this is treated in the
  spectral simulation code Cloudy, and present numerical simulations of
  environments where this temperature indicator is used, with a detailed
  treatment of the physical processes that determine level populations
  within H<SUP>0</SUP>. We discuss situations where this temperature
  indicator traces T <SUB> K </SUB>, cases where it fails, as well as
  the effects of Lyα pumping on the 21 cm spin temperature. We also
  show that the Lyα excitation temperature rarely traces the gas
  kinetic temperature.

Title: A Grid of Synthetic Spectra for Hot DA White Dwarfs and Its
    Application in Stellar Population Synthesis
Authors: Levenhagen, Ronaldo S.; Diaz, Marcos P.; Coelho, Paula R. T.;
   Hubeny, Ivan
Bibcode: 2017ApJS..231....1L
Altcode: 2017arXiv170704299L
  In this work we present a grid of LTE and non-LTE synthetic spectra
  of hot DA white dwarfs (WDs). In addition to its usefulness for the
  determination of fundamental stellar parameters of isolated WDs and
  in binaries, this grid will be of interest for the construction of
  theoretical libraries for stellar studies from integrated light. The
  spectral grid covers both a wide temperature and gravity range, with
  17,000 K ≤ T <SUB>eff</SUB> ≤ 100,000 K and 7.0 ≤ {log}g ≤
  9.5. The stellar models are built for pure hydrogen and the spectra
  cover a wavelength range from 900 Å to 2.5 μm. Additionally, we derive
  synthetic HST/ACS, HST/WFC3, Bessel UBVRI, and SDSS magnitudes. The
  grid was also used to model integrated spectral energy distributions
  of simple stellar populations and our modeling suggests that DAs might
  be detectable in ultraviolet bands for populations older than ∼8 Gyr.

Title: VizieR Online Data Catalog: Hot DA white dwarfs grid of
    synthetic spectra (Levenhagen+, 2017)
Authors: Levenhagen, R. S.; Diaz, M. P.; Coelho, P. R. T.; Hubeny, I.
Bibcode: 2017yCat..22310001L
Altcode:
  Files tTTTgGGA.dat concern non-LTE DA White Dwarf synthetic spectra. TTT
  corresponds to the effective temperature, GG corresponds to log(g)
  and nl (for NLTE) flag. Files bessel.dat, hstacs.dat, hstwfc3.dat,
  sdss.dat are respectively synthetic magnitude tables in the Bessel,
  HST/ACS, HST/WFC3 and SLOAN/SDSS systems. <P />(8 data files).

Title: TLUSTY User's Guide II: Reference Manual
Authors: Hubeny, Ivan; Lanz, Thierry
Bibcode: 2017arXiv170601935H
Altcode:
  This is the second part of a three-volume guide to TLUSTY and
  SYNSPEC. It presents a detailed reference manual for TLUSTY, which
  contains a detailed description of basic physical assumptions and
  equations used to model an atmosphere, together with an overview of
  the numerical methods to solve these equations.

Title: A brief introductory guide to TLUSTY and SYNSPEC
Authors: Hubeny, Ivan; Lanz, Thierry
Bibcode: 2017arXiv170601859H
Altcode:
  This is the first of three papers that present a detailed guide for
  working with the codes {\sc tlusty} and {\sc synspec} to generate
  model stellar atmospheres or accretion disks, and to produce detailed
  synthetic spectra. In this paper, we present a very brief manual
  intended for casual users who intend to use these codes for simple,
  well defined tasks. This paper does not present any background theory,
  or a description of the adopted numerical approaches, but instead uses
  simple examples to explain how to employ these codes. In particular,
  it shows how to produce a simple model atmosphere from the scratch,
  or how to improve an existing model by considering more extended model
  atoms. This paper also presents a brief guide to the spectrum synthesis
  program {\sc synspec}.

Title: TLUSTY User's Guide III: Operational Manual
Authors: Hubeny, Ivan; Lanz, Thierry
Bibcode: 2017arXiv170601937H
Altcode:
  This paper presents a detailed operational manual for TLUSTY. It
  provides a guide for understanding the essential features and the basic
  modes of operation of the program. To help the user, it is divided
  into two parts. The first part describes the most important input
  parameters and available numerical options. The second part covers
  additional details and a comprehensive description of all physical
  and numerical options, and a description of all input parameters,
  many of which needed only in special cases.

Title: Effective temperatures of cataclysmic-variable white dwarfs
    as a probe of their evolution
Authors: Pala, A. F.; Gänsicke, B. T.; Townsley, D.; Boyd, D.;
   Cook, M. J.; De Martino, D.; Godon, P.; Haislip, J. B.; Henden,
   A. A.; Hubeny, I.; Ivarsen, K. M.; Kafka, S.; Knigge, C.; LaCluyze,
   A. P.; Long, K. S.; Marsh, T. R.; Monard, B.; Moore, J. P.; Myers,
   G.; Nelson, P.; Nogami, D.; Oksanen, A.; Pickard, R.; Poyner, G.;
   Reichart, D. E.; Rodriguez Perez, D.; Schreiber, M. R.; Shears, J.;
   Sion, E. M.; Stubbings, R.; Szkody, P.; Zorotovic, M.
Bibcode: 2017MNRAS.466.2855P
Altcode: 2017arXiv170102738P
  We present HST spectroscopy for 45 cataclysmic variables (CVs), observed
  with HST/COS and HST/STIS. For 36 CVs, the white dwarf is recognisable
  through its broad Ly α absorption profile and we measure the white
  dwarf effective temperatures (T<SUB>eff</SUB>) by fitting the HST data
  assuming log g = 8.35, which corresponds to the average mass for CV
  white dwarfs (≃0.8 M<SUB>⊙</SUB>). Our results nearly double the
  number of CV white dwarfs with an accurate temperature measurement. We
  find that CVs above the period gap have, on average, higher temperatures
  (&lt;T<SUB>eff</SUB>&gt; ≃ 23 000 K) and exhibit much more scatter
  compared to those below the gap (&lt;T<SUB>eff</SUB>&gt; ≃ 15 000
  K). While this behaviour broadly agrees with theoretical predictions,
  some discrepancies are present: (I) all our new measurements above the
  gap are characterized by lower temperatures (T<SUB>eff</SUB> ≃ 16
  000-26 000 K) than predicted by the present-day CV population models
  (T<SUB>eff</SUB> ≃ 38 000-43 000 K); (II) our results below the
  gap are not clustered in the predicted narrow track and exhibit in
  particular a relatively large spread near the period minimum, which
  may point to some shortcomings in the CV evolutionary models. Finally,
  in the standard model of CV evolution, reaching the minimum period,
  CVs are expected to evolve back towards longer periods with mean
  accretion rates dot{M}≲ 2 × 10^{-11} M_{⊙} yr^{-1}, corresponding
  to T<SUB>eff</SUB> ≲ 11 500 K. We do not unambiguously identify any
  such system in our survey, suggesting that this major component of
  the predicted CV population still remains elusive to observations.

Title: Hot DA white dwarf model atmosphere calculations: including
    improved Ni PI cross-sections
Authors: Preval, S. P.; Barstow, M. A.; Badnell, N. R.; Hubeny, I.;
   Holberg, J. B.
Bibcode: 2017MNRAS.465..269P
Altcode: 2016arXiv161009662P
  To calculate realistic models of objects with Ni in their atmospheres,
  accurate atomic data for the relevant ionization stages need to
  be included in model atmosphere calculations. In the context of
  white dwarf stars, we investigate the effect of changing the Ni
  IV-VI bound-bound and bound-free atomic data on model atmosphere
  calculations. Models including photoionization cross-section (PICS)
  calculated with AUTOSTRUCTURE show significant flux attenuation of up
  to ∼80 per cent shortward of 180 Å in the extreme ultraviolet (EUV)
  region compared to a model using hydrogenic PICS. Comparatively, models
  including a larger set of Ni transitions left the EUV, UV, and optical
  continua unaffected. We use models calculated with permutations of these
  atomic data to test for potential changes to measured metal abundances
  of the hot DA white dwarf G191-B2B. Models including AUTOSTRUCTURE
  PICS were found to change the abundances of N and O by as much as
  ∼22 per cent compared to models using hydrogenic PICS, but heavier
  species were relatively unaffected. Models including AUTOSTRUCTURE PICS
  caused the abundances of N/O IV and V to diverge. This is because the
  increased opacity in the AUTOSTRUCTURE PICS model causes these charge
  states to form higher in the atmosphere, more so for N/O V. Models
  using an extended line list caused significant changes to the Ni IV-V
  abundances. While both PICS and an extended line list cause changes
  in both synthetic spectra and measured abundances, the biggest changes
  are caused by using AUTOSTRUCTURE PICS for Ni.

Title: Probing Supernovae Chemical Yields in Low Metallicity
    Environments with UV Spectroscopy of Magellanic Cloud B-type Stars
Authors: Lanz, Thierry; Adelman, Saul J.; Bouret, Jean-Claude;
   Gulliver, Austin F.; Hill, Graham; Hubeny, Ivan; Peters, Geraldine J.;
   Pickering, Juliet C.; Proffitt, Charles R.
Bibcode: 2016hst..prop14081L
Altcode:
  Spectrum synthesis studies of the UV spectra of sharp-lined
  main sequence B stars provide astronomers with some of the best
  determinations of the abundances of the light, Fe group, and neutron
  capture elements. B stars are therefore best-suited to study the
  chemical evolution of the Magellanic Clouds. But the HST archive
  is virtually devoid of high resolution spectra of such objects. We
  propose FUV and NUV observations with the COS G130M, G160M, G185M,
  and G225M gratings. The four program stars have been observed with
  the FUSE spacecraft, hence this project will produce continuous
  high-resolution spectral coverage from 950 to 2400 A and provide a
  permanent archive of fundamental spectra from which ground-breaking
  studies of the Magellanic Clouds can be performed in the decades
  to come. This limited program aims at producing an extragalactic,
  low-metallicity counterpart to the bright star library of early B
  stars that is currently being obtained as part of the HST Cycle 21
  Treasury program "Advanced Spectral Library II: Hot Stars" (GO 13346,
  PI T. Ayres). <P />Spectral lines from most Fe group and s-process
  elements are found only in the UV region in B stars and information
  on their abundances is important for studying the chemical evolution
  of a galaxy, computing opacities for stellar evolution calculations,
  and assessing the validity of theoretical calculations of explosive
  nucleosynthesis. Comparing the derived abundances of iron-peak and
  heavier elements in galactic and Magellanic Cloud B main sequence
  stars will provide an empirical probe of chemical yields ejected by
  evolved stars and supernovae in different environments.

Title: Spectroscopy from the Hubble Space Telescope Cosmic Origins
    Spectrograph of the Southern Nova-like BB Doradus in an Intermediate
    State
Authors: Godon, Patrick; Sion, Edward M.; Gänsicke, Boris T.; Hubeny,
   Ivan; de Martino, Domitilla; Pala, Anna F.; Rodríguez-Gil, Pablo;
   Szkody, Paula; Toloza, Odette
Bibcode: 2016ApJ...833..146G
Altcode: 2017arXiv170105222G
  We present a spectral analysis of the spectrum from the Hubble Space
  Telescope Cosmic Origins Spectrograph (HST/COS) of the southern
  VY Scl nova-like variable BB Doradus, obtained as part of a Cycle
  20 HST/COS survey of accreting white dwarfs (WDs) in cataclysmic
  variables. BB Dor was observed with COS during an intermediate state
  with a low mass accretion rate, thereby allowing an estimate of the
  WD temperature. The results of our spectral analysis show that the
  WD is a significant far-ultraviolet (FUV) component of the spectrum
  with a temperature of about 35,000-50,000 K, assuming a WD mass of
  0.80 {M}<SUB>⊙ </SUB>({log}(g)=8.4). The disk, with a mass accretion
  rate of ≈ {10}<SUP>-10</SUP> {M}<SUB>⊙ </SUB> {{yr}}<SUP>-1</SUP>,
  contributes about 1/5 to 1/2 of the FUV flux.

Title: GW Librae: a unique laboratory for pulsations in an accreting
    white dwarf
Authors: Toloza, O.; Gänsicke, B. T.; Hermes, J. J.; Townsley, D. M.;
   Schreiber, M. R.; Szkody, P.; Pala, A.; Beuermann, K.; Bildsten, L.;
   Breedt, E.; Cook, M.; Godon, P.; Henden, A. A.; Hubeny, I.; Knigge,
   C.; Long, K. S.; Marsh, T. R.; de Martino, D.; Mukadam, A. S.; Myers,
   G.; Nelson, P.; Oksanen, A.; Patterson, J.; Sion, E. M.; Zorotovic, M.
Bibcode: 2016MNRAS.459.3929T
Altcode: 2016arXiv160402162T; 2016MNRAS.tmp..639T; 2016MNRAS.tmp..623T
  Non-radial pulsations have been identified in a number of accreting
  white dwarfs in cataclysmic variables. These stars offer insight
  into the excitation of pulsation modes in atmospheres with mixed
  compositions of hydrogen, helium, and metals, and the response of
  these modes to changes in the white dwarf temperature. Among all
  pulsating cataclysmic variable white dwarfs, GW Librae stands out by
  having a well-established observational record of three independent
  pulsation modes that disappeared when the white dwarf temperature rose
  dramatically following its 2007 accretion outburst. Our analysis of
  Hubble Space Telescope (HST) ultraviolet spectroscopy taken in 2002,
  2010, and 2011, showed that pulsations produce variations in the white
  dwarf effective temperature as predicted by theory. Additionally in
  2013 May, we obtained new HST/Cosmic Origin Spectrograph ultraviolet
  observations that displayed unexpected behaviour: besides showing
  variability at ≃275 s, which is close to the post-outburst
  pulsations detected with HST in 2010 and 2011, the white dwarf exhibits
  high-amplitude variability on an ≃4.4 h time-scale. We demonstrate
  that this variability is produced by an increase of the temperature of
  a region on white dwarf covering up to ≃30 per cent of the visible
  white dwarf surface. We argue against a short-lived accretion episode
  as the explanation of such heating, and discuss this event in the
  context of non-radial pulsations on a rapidly rotating star.

Title: Wide band spectra of nova-like variables: A confrontation of
    observations with theory
Authors: Long, Knox S.; Higginbottom, Nick; Hubeny, Ivan; Knigge,
   Christian; Matthews, James; Sim, Stuart A.
Bibcode: 2016hst..prop14637L
Altcode:
  Nova-like variables are the best and nearest examples of steady-state
  disk accretion onto a compact object. Emission in these system arises
  from a large number of components, including the WD and secondary
  star, the accretion disk through which mass is accreted, and a wind
  through which mass is lost. However, the only wide band ''spectra''
  of these variable objects have been constructed by stitching together
  spectra obtained at different times, and as a result it is difficult to
  conclude exactly what is causing the departures from the predictions of
  steady-state accretion disk models that are observed, or to establish
  the geometry of the wind in these systems. This is a project to
  use HST/STIS to obtain single-epoch, FUV-near IR spectra of five
  bright nova-like variables, with varying inclinations, to remedy this
  problem. We will compare this benchmark set of spectra to new models of
  the disks and winds for this group of cataclysmic variables in order to
  measure the temperature profiles of the disks, to determine mass loss
  rates, collimation, and other physical characteristics of the winds,
  and to assess the overall effect of the dense regions of the wind on
  the spectral energy distribution.

Title: Division G Commission 36: Theory of Stellar Atmospheres
Authors: Puls, Joachim; Hubeny, Ivan; Asplund, Martin; Allard, France;
   Allende Prieto, Carlos; Ayres, Thomas R.; Carlsson, Mats; Gustafsson,
   Bengt; Kudritzki, Rolf-Peter; Ryabchikova, Tatiana A.
Bibcode: 2016IAUTA..29..453P
Altcode:
  Different from previous triennial reports, this report covers the
  activities of IAU Commission 36 `Theory of Stellar Atmospheres'
  over the past six years†, and will be the last report from the
  `old' Commission 36. After the General Assembly in Honolulu (August
  2015), a new Commission `Stellar and Planetary Atmospheres' (C.G5,
  under Division G, `Stars and Stellar Physics') has come into life,
  and will continue our work devoted to the outer envelopes of stars,
  as well as extend it to the atmospheres of planets (see Sect. 4).

Title: Does star formation proceed differently in metal-poor galaxies?
Authors: Lebouteiller, vianney; Aloisi, Alessandra; Barlow, Michael J.;
   Cormier, Diane; Galliano, Frederic; Glover, Simon; Heap, Sara Ridgway;
   Hubeny, Ivan; James, Bethan Lesley; Karczewski, Oskar; Kunth, Daniel;
   Le Bourlot, Jacques; Le Petit, Franck; Lehner, Nicolas; Madden,
   Suzanne; Remy, Aurelie
Bibcode: 2015hst..prop13697L
Altcode:
  The importance of molecular gas in the star-formation process has been
  questioned by recent theoretical studies. When metals are scarce,
  star formation could proceed before the molecular fraction becomes
  significant, making cold atomic gas the key pre-requisite for star
  formation. The best case studies are blue compact dwarf galaxies (BCDs),
  with their prominent star-formation episode and yet with little or no
  evidence of molecular gas. Current observations do not provide strong
  constraints on the presence of dense atomic gas in BCDs nor on the
  fraction of molecular gas. <P />We propose to examine the HI region
  of 9 nearby BCDs selected from the Herschel Dwarf Galaxy Survey. Our
  program relies on the synergy of Hubble and Herschel, by calculating
  the gas cooling rate from the fine-structure level of ionized carbon,
  a parameter that can be determined both in the FUV with COS (probing
  the diffuse gas through the 1335.7A CII* absorption) and in the FIR with
  Herschel (probing the denser gas through the [CII] 157um emission). This
  comparison allows us to constrain the volume filling factor of dense
  vs. diffuse gas. The program we propose will allow us to examine how
  this fraction varies with metallicity, star-formation rate, and total
  gas mass. We will also be able to quantify the mass of molecular gas and
  evaluate its actual importance for star formation. Finally, a secondary
  objective is to characterize the main gas heating mechanisms in the
  HI region of BCDs and in particular the validity of the photoelectric
  effect paradigm in sources with a low dust-to-gas ratio, with potential
  implications for high-redshift galaxies.

Title: Tables of phase functions, opacities, albedos, equilibrium
    temperatures, and radiative accelerations of dust grains in exoplanets
Authors: Budaj, J.; Kocifaj, M.; Salmeron, R.; Hubeny, I.
Bibcode: 2015MNRAS.454....2B
Altcode: 2015arXiv150508013B
  There has been growing observational evidence for the presence of
  condensates in the atmospheres and/or comet-like tails of extrasolar
  planets. As a result, systematic and homogeneous tables of dust
  properties are useful in order to facilitate further observational
  and theoretical studies. In this paper we present calculations and
  analysis of non-isotropic phase functions, asymmetry parameter (mean
  cosine of the scattering angle), absorption and scattering opacities,
  single scattering albedos, equilibrium temperatures, and radiative
  accelerations of dust grains relevant for extrasolar planets. Our
  assumptions include spherical grain shape, Deirmendjian particle
  size distribution, and Mie theory. We consider several species:
  corundum/alumina, perovskite, olivines with 0 and 50 per cent iron
  content, pyroxenes with 0, 20, and 60 per cent iron content, pure iron,
  carbon at two different temperatures, water ice, liquid water, and
  ammonia. The presented tables cover the wavelength range of 0.2-500 μm
  and modal particle radii from 0.01 to 100 μm. Equilibrium temperatures
  and radiative accelerations assume irradiation by a non-blackbody source
  of light with temperatures from 7000 to 700 K seen at solid angles from
  2π to 10<SUP>-6</SUP> sr. The tables are provided to the community
  together with a simple code which allows for an optional, finite,
  angular dimension of the source of light (star) in the phase function.

Title: The Wind and Photosphere of the Unique DO White Dwarf RE
    J0503-289
Authors: Barstow, Martin; Holberg, Jay B.; Hubeny, Ivan; Lanz, Thierry;
   Sion, Edward M.
Bibcode: 2015hst..prop.6628B
Altcode:
  We propose to obtain high S/N GHRS spectra of the key He-richwhite dwarf
  RE J0503-289. These observations have twoprincipal aims. The first
  is to investigate the phenomenon ofmass loss in this star. Excluding
  planetary nebulae nuclei, REJ0503-289 is the only white dwarf in which
  evidence of ongoingmass loss has been observed with IUE. However, the
  reporteddetection is near the limit of the sensitivity of IUEpreventing
  study of the wind during its less intense periods.Mass loss may well be
  the missing ingredient in thetheoretical description of heavy element
  abundances in whitedwarfs. RE J0503-289 is the only known white dwarf
  where thiseffect can be studied as an on going phenomenon. The secondaim
  is to search for Fe and Ni in the photosphere of thisstar. The presence
  of these elements is required to explainthe large flux deficit observed
  in the EUV. Detailed models,including those elements so far detected (C,
  N, O and Si),substantially over predict EUV flux levels. RE J0503-289
  isalso the only DO white dwarf for which a joint analysis of EUVand UV
  data will be possible and for which we can conduct adefinitive study
  of the composition and structure of thephotosphere.

Title: GW Lib: a Unique Laboratory for White Dwarf Pulsations
Authors: Toloza, Odette; Gänsicke, Boris T.; Hermes, JJ; Townsley,
   Dean M.; Szkody, Paula; Beuermann, K.; Bildsten, Lars; de Martino,
   D.; Godon, Patrick; Henden, Arne A.; Hubeny, Ivan; Knigge, Christian;
   Long, Knox S.; Marsh, T. R.; Patterson, Joseph; Schreiber, M. R.;
   Sion, Edward M.; Zorotovic, Monica
Bibcode: 2015ASPC..493..253T
Altcode:
  Non-radial pulsations have been identified in a number of accreting
  white dwarfs in cataclysmic variables. These stars offer insight into
  the excitation of pulsation modes in mixed H/He/Z atmospheres, and the
  response of these modes to changes in the white dwarf temperature. Among
  all pulsating cataclysmic variable white dwarfs, GW Lib stands out by
  having a well-established observational record of three independent
  pulsation modes that were wiped out during its 2007 outburst. We
  have obtained new HST ultraviolet observations in May 2013 that show
  an unexpected behaviour: besides some activity near the ∼280 s
  period that has been observed in the past, the white dwarf underwent
  a large-amplitude brightening. We demonstrate that the brightening is
  related to an increase of the photospheric temperature, argue against
  an accretion episode as explanation, and discuss this event in the
  context of non-radial pulsations on a rapidly rotating star.

Title: A Possible Solution to the Lyman/Balmer Line Problem in Hot
    DA White Dwarfs
Authors: Preval, Simon P.; Barstow, Martin A.; Badnell, Nigel R.;
   Holberg, Jay B.; Hubeny, Ivan
Bibcode: 2015ASPC..493...15P
Altcode: 2014arXiv1410.0811P
  Arguably, the best method for determining the effective temperature
  (T<SUB>eff</SUB>) and surface gravity (log g) of a DA white dwarf is
  by fitting the Hydrogen Lyman and Balmer absorption features. However,
  as has been shown for white dwarfs with T<SUB>eff</SUB>&gt;50,000K,
  the calculated value from the Lyman and Balmer lines are discrepant,
  which worsens with increasing temperature. Many different solutions
  have been suggested, ranging from the input physics used to calculate
  the models, to interstellar reddening. We will focus on the former,
  and consider three variables. The first is the atomic data used, namely
  the number of transitions included in line blanketing treatments and
  the photoionization cross sections. The second is the stark broadening
  treatment used to synthesise the Lyman and Balmer line profiles, namely
  the calculations performed by Lemke (1997) and Tremblay &amp; Bergeron
  (2009). Finally, the third is the atmospheric content. The model
  grids are calculated with a pure H composition, and a metal polluted
  composition using the abundances of Preval et al. (2013). We present
  the preliminary results of our analysis, whereby we have determined the
  T<SUB>eff</SUB> for a small selection of white dwarfs. We plan to extend
  our analysis by allowing metallicity to vary in future model grids.

Title: An Intensive HST/COS Study of 31 CV WDs
Authors: Pala, A. F.; Gänsicke, B. T.; Beuermann, K.; Bildsten, L.;
   De Martino, D.; Godon, P.; Henden, A. A.; Hubeny, I.; Knigge, C.;
   Long, K. S.; Marsh, T. R.; Patterson, J.; Schreiber, M. R.; Sion,
   E. M.; Szkody, P.; Townsley, D.; Zorotovic, M.
Bibcode: 2015ASPC..493..521P
Altcode:
  Accretion is the key ingredient in the evolution of white dwarfs
  (WDs) in cataclysmic variables (CVs), with important implications for
  their potential as progenitors for Type Ia Supernovae. The effective
  temperature (T<SUB>eff</SUB>) gives a direct measure of the average
  accretion rate and we report here the T<SUB>eff</SUB> measurement
  for 31 CV WDs, observed as a part of a 122 orbit HST program. The HST
  spectra alone cannot resolve the degeneracy between T<SUB>eff</SUB>
  and the surface gravity log g, and we will use phase-resolved X-Shooter
  observations to (i) measure the mass ratio of the CVs from the reflex
  motion of both the WD and the donor star (ii) to establish the spectral
  energy distribution (SED), which constrains both T<SUB>eff</SUB>
  and log g. Combining the X-Shooter and HST data, we can measure the
  WD masses to a few percent, and will be able to answer the question
  whether accreting CV WDs grow in mass.

Title: Refining our Knowledge of the White Dwarf Mass-Radius Relation
    with HST Observations of Sirius-type Binaries
Authors: Barstow, M. A.; Bond, H. E.; Burleigh, M. R.; Casewell,
   S. L.; Farihi, J.; Holberg, J. B.; Hubeny, I.
Bibcode: 2015ASPC..493..307B
Altcode:
  The presence of a white dwarf in a resolved binary system, such as
  Sirius, provides an opportunity to combine dynamical information about
  the masses, from astrometry and spectroscopy, with a gravitational
  red-shift measurement and spectrophotometry of the white dwarf
  atmosphere to provide a test of theoretical mass-radius relations of
  unprecedented accuracy. We demonstrated this with the first Balmer
  line spectrum of Sirius B to be obtained free of contamination from
  the primary, with STIS on HST. However, we also found an unexplained
  discrepancy between the spectroscopic and gravitational red-shift
  mass determinations. With the recovery of STIS, we have been able to
  revisit our observations of Sirius B with an improved observation
  strategy designed to reduce systematic errors on the gravitational
  red-shift measurement. We provide a preliminary report on the refined
  precision of the Sirius B mass-radius measurements and the extension
  of this technique to a larger sample of white dwarfs in resolved
  binaries. Together these data can provide accurate mass and radius
  determinations capable of testing the theoretical mass-radius relation
  and distinguishing between possible structural models.

Title: Refining our knowledge of the white dwarf mass-radius relation
Authors: Barstow, M. A.; Bond, H. E.; Burleigh, M. R.; Casewell,
   S. L.; Farihi, J.; Holberg, J. B.; Hubeny, I.
Bibcode: 2015arXiv150503427B
Altcode:
  The presence of a white dwarf in a resolved binary system, such as
  Sirius, provides an opportunity to combine dynamical information about
  the masses, from astrometry and spectroscopy, with a gravitational
  red-shift measurement and spectrophotometry of the white dwarf
  atmosphere to provide a test of theoretical mass-radius relations of
  unprecedented accuracy. We demonstrated this with the first Balmer
  line spectrum of Sirius B to be obtained free of contamination from
  the primary, with STIS on HST. However, we also found an unexplained
  discrepancy between the spectroscopic and gravitational red-shift
  mass determinations. With the recovery of STIS, we have been able to
  revisit our observations of Sirius B with an improved observation
  strategy designed to reduce systematic errors on the gravitational
  red-shift measurement. We provide a preliminary report on the refined
  precision of the Sirius B mass-radius measurements and the extension
  of this technique to a larger sample of white dwarfs in resolved
  binaries. Together these data can provide accurate mass and radius
  determinations capable of testing the theoretical mass-radius relation
  and distinguishing between possible structural models.

Title: Population III Stars in I Zw 18
Authors: Heap, Sally; Bouret, Jean-Claude; Hubeny, Ivan
Bibcode: 2015arXiv150402742H
Altcode:
  Ultraviolet and 21-cm observations suggest that the extremely
  low-metallicity galaxy, I Zw 18, is a stream-fed galaxy containing
  a "pocket" of pristine stars responsible for producing nebular He
  II recombination emission observed in I Zw18-NW. Far-UV spectra by
  Hubble/COS and the Far Ultraviolet Spectroscopic Explorer (FUSE)
  make this suggestion conclusive by demonstrating that the spectrum
  of I Zw 18-NW shows no metal lines like O VI 1032, 1038 of comparable
  ionization as the He II recombination emission.

Title: Non-LTE Abundances in OB stars: Preliminary Results for 5
    Stars in the Outer Galactic Disk
Authors: Bragançca, G. A.; Lanz, T.; Daflon, S.; Cunha, K.; Garmany,
   C. D.; Glaspey, J. W.; Borges Fernandes, M.; Oey, M. S.; Bensby, T.;
   Hubeny, I.
Bibcode: 2015IAUS..307...90B
Altcode: 2014arXiv1408.5807B
  The aim of this study is to analyse and determine elemental abundances
  for a large sample of distant B stars in the outer Galactic disk in
  order to constrain the chemical distribution of the Galactic disk and
  models of chemical evolution of the Galaxy. Here, we present preliminary
  results on a few stars along with the adopted methodology based on
  securing simultaneous O and Si ionization equilibria with consistent
  NLTE model atmospheres.

Title: A large HST program: effective temperatures of cataclysmic
    variable white dwarfs
Authors: Pala, A. F.; Gaensicke, B.; Beuermann, K.; Bildsten, L.;
   de Martino, D.; Godon, P.; Henden, A.; Hubeny, I.; Knigge, C.; Long,
   K.; Marsh, T.; Patterson, J.; Schreiber, M. R.; Sion, E. M.; Szkody,
   P.; Townsley, D.; Zorotovic, M.
Bibcode: 2015gacv.workE..32P
Altcode: 2015PoS...255E..32P
  No abstract at ADS

Title: 3D Gray Radiative Properties of a Radiation Hydrodynamic
    Model of a YSO Accretion Shock
Authors: Ibgui, L.; de Sá, L.; Stehlé, C.; Chièze, J. -P.; Orlando,
   S.; Hubeny, I.; Lanz, T.; Matsakos, T.; González, M.; Bonito, R.
Bibcode: 2014ASPC..488...83I
Altcode:
  We present preliminary results of radiative properties of a 1D gray
  radiation hydrodynamic (RHD) model of an accretion shock on a young
  stellar object (YSO). This model takes into account the transition
  between the collisional equilibrium regime (local thermodynamic
  equilibrium, LTE), and the coronal equilibrium regime. Based on the
  1D planar structure, we built a 3D cylindrical one. Most notably,
  the post-shock region obtained in our case is far less extended (by
  a factor of 10 000) than the typical one obtained with models that
  assume gray optically thin radiative losses. Moreover, we find that
  the column is optically thin in its longitudinal dimension, and in the
  transverse dimension, except over an extremely narrow region (≲ 700
  m). Consequently, still under the gray assumption, the photons emitted
  by the hot slab can propagate through the column and escape freely in
  all directions, including towards the chromosphere. The radiation flux
  has therefore components that are perpendicular to the accretion column,
  which demonstrates that a multidimensional (2D or 3D) radiative model
  is necessary for such a cylindrical structure. This study needs to
  be taken forward and expanded, by improving the radiative treatment
  of the RHD model, through relaxation of both the gray and the LTE
  approximations for the calculation of opacities, in order to clarify
  the structure of the post-shock region, which is a major source of
  emission probed by observations.

Title: Evidence for an external origin of heavy elements in hot DA
    white dwarfs
Authors: Barstow, M. A.; Barstow, J. K.; Casewell, S. L.; Holberg,
   J. B.; Hubeny, I.
Bibcode: 2014MNRAS.440.1607B
Altcode: 2014MNRAS.tmp..544B; 2014arXiv1402.2164B
  We present a series of systematic abundance measurements for 89 hydrogen
  atmosphere (DA-type) white dwarfs with temperatures spanning 16 000-77
  000 K drawn from the FUSE spectral archive. This is the largest study to
  date of white dwarfs where radiative forces are significant, exceeding
  our earlier work, based mainly on International Ultraviolet Explorer
  and Hubble Space Telescope data, by a factor 3. Using heavy element
  blanketed non-local thermodynamic equilibrium stellar atmosphere
  calculations, we have addressed the heavy element abundance patterns
  making completely objective measurements of abundance values and
  their error ranges using a χ<SUP>2</SUP> fitting technique. We
  are able to establish the broad range of abundances seen in a given
  temperature range and establish the incidence of stars which appear,
  in the optical, to be atmospherically devoid of any material other
  than H. We compare the observed abundances to predictions of radiative
  levitation calculations, revealing little agreement. We propose that
  the supply of heavy elements is accreted from external sources rather
  than being intrinsic to the star. These elements are then retained
  in the white dwarf atmospheres by radiative levitation, a model that
  can explain both the diversity of measured abundances for stars of
  similar temperature and gravity, including cases with apparently pure
  H envelopes, and the presence of photospheric metals at temperatures
  where radiative levitation is no longer effective.

Title: The Discovery of Pulsating Hot Subdwarfs in NGC 2808
Authors: Brown, T.; Landsman, W.; Randall, S.; Sweigart, A.; Lanz,
   T.; Hubeny, I.
Bibcode: 2014ASPC..481...29B
Altcode:
  We present preliminary results of a Hubble Space Telescope program
  to search for pulsating hot subdwarfs in the core of NGC 2808. These
  observations, obtained in March of 2013, were motivated by the recent
  discovery of such stars in the outskirts of ω Cen. Both ω Cen and
  NGC 2808 are massive globular clusters exhibiting complex stellar
  populations and large numbers of extreme horizontal branch stars. Our
  far-UV photometric monitoring of over 100 UV-bright stars has revealed
  at least six pulsating subdwarfs with periods ranging from 100 to
  150 seconds. In the UV color-magnitude diagram of NGC 2808, all six
  of these stars lie immediately below the canonical horizontal branch,
  a region populated by the subluminous “blue hook” stars. Three of
  these six pulsators also have low-resolution far-UV spectroscopy that
  is sufficient to broadly constrain their atmospheric abundances and
  effective temperatures. Curiously, the spectroscopic and photometric
  data do not exhibit the uniformity one might expect from a well-defined
  instability strip.

Title: Synthetic Spectra for O and B Type Subdwarf Stars
Authors: Nemeth, P.; Östensen, R.; Tremblay, P.; Hubeny, I.
Bibcode: 2014ASPC..481...95N
Altcode: 2013arXiv1308.0252N
  We present a grid of optical (3200-7200 Å) synthetic spectra calculated
  with TLUSTY/SYNSPEC. The new NLTE model atmospheres include the most
  recent hydrogen Stark broadening profiles; were calculated in opacity
  sampling and limited to pure H/He composition. The grid covers the
  observed parameter space of (He-)sdB and (He-)sdO stars, therefore it
  is suitable for the homogeneous spectral analyses of such evolved stars.

Title: 3D Gray Radiative Properties of Accretion Shocks in Young
    Stellar Objects
Authors: Ibgui, L.; Orlando, S.; Stehlé, C.; Chièze, J. -P.; Hubeny,
   I.; Lanz, T.; de Sá, L.; Matsakos, T.; González, M.; Bonito, R.
Bibcode: 2014EPJWC..6404005I
Altcode:
  We address the problem of the contribution of radiation to the structure
  and dynamics of accretion shocks on Young Stellar Objects. Solving the
  3D RTE (radiative transfer equation) under our "gray LTE approach",
  i.e., using appropriate mean opacities computed in local thermodynamic
  equilibrium, we post-process the 3D MHD (magnetohydrodynamic) structure
  of an accretion stream impacting the stellar chromosphere. We find a
  radiation flux of ten orders of magnitude larger than the accreting
  energy rate, which is due to a large overestimation of the radiative
  cooling. A gray LTE radiative transfer approximation is therefore
  not consistent with the given MHD structure of the shock. Further
  investigations are required to clarify the role of radiation, by
  relaxing both the gray and LTE approximations in RHD (radiation
  hydrodynamics) simulations. Post-processing the obtained structures
  through the resolution of the non-LTE monochromatic RTE will provide
  reference radiation quantities against which RHD approximate solutions
  will be compared.

Title: Theory of Stellar Atmospheres
Authors: Hubeny, Ivan; Mihalas, Dimitri
Bibcode: 2014tsa..book.....H
Altcode:
  No abstract at ADS

Title: Accretion shock stability on a dynamically heated YSO
    atmosphere with radiative transfer
Authors: de Sá, Lionel; Chièze, Jean-Pierre; Stehlé, Chantal;
   Matsakos, Titos; Ibgui, Laurent; Lanz, Thierry; Hubeny, Ivan
Bibcode: 2014EPJWC..6404002D
Altcode:
  Theory and simulations predict Quasi-Periodic Oscillations of
  shocks which develop in magnetically driven accretion funnels
  connecting the stellar disc to the photosphere of Young Stellar
  Objects (YSO). X-ray observations however do not show evidence of
  the expected periodicity. We examine here, in a first attempt, the
  influence of radiative transfer on the evolution of material impinging
  on a dynamically heated stellar atmosphere, using the 1D ALE-RHD code
  ASTROLABE. The mechanical shock heating mechanism of the chromosphere
  only slightly perturbs the flow. We also show that, since the impacting
  flow, and especially the part which penetrates into the chromosphere,
  is not treated as a purely radiating transparent medium, a sufficiently
  efficient coupling between gas and radiation may affect or even suppress
  the oscillations of the shocked column. This study shows the importance
  of the description of the radiation effects in the hydrodynamics and
  of the accuracy of the opacities for an adequate modeling.

Title: DISKSPEC: A Tool for Analyzing Observed Spectra of Accretion
    Disk Systems
Authors: Hubeny, Ivan
Bibcode: 2013hst..prop13251H
Altcode:
  Accretion disks are ubiquitous in astronomy, associated with AGN,
  stellar mass black holes, X-ray binaries, progenitors of Ia supernovae,
  X-ray binaries, cataclysmic variables {CVs} {ordinary, recurrent, and
  dwarf novae, novalikes}, pre-main sequence stars. An understanding of
  the nature of, and physical processes in, accretion disks is one of
  the central themes in astrophysics. A large number of past, present,
  and future HST observational programs were/are/will be devoted to
  astronomical systems that harbor an accretion disk. We propose to
  develop a package DISKSPEC, which enables the user to generate a
  synthetic spectum of an accretion disk for essentially any combination
  of input parameters. The strategy is to use a sufficiently dense and
  extended grid of models for genericdisk rings, and to develop a code
  that computes a spectrum of the whole disk by interpolating the generic
  grid spectra to the actual spectra emergent from the individual radial
  rings of the disk, and integrates over the disk taking into account
  Doppler shifts due to disk rotation. We believe that the package will
  serve many researchers using new or archival HST data to be able to
  perform a spectroscopic analysis of objects that contain an accretion
  disk in a fast and flexible way, and thus contribute significantly to
  a better use of past, present, and future HST observations.

Title: Binary Star Synthetic Photometry and Distance Determination
    Using BINSYN
Authors: Linnell, Albert P.; DeStefano, Paul; Hubeny, Ivan
Bibcode: 2013AJ....146...68L
Altcode:
  This paper extends synthetic photometry to components of binary star
  systems. The paper demonstrates accurate recovery of single star
  photometric properties for four photometric standards, Vega, Sirius,
  GD153, and HD209458, ranging over the HR diagram, when their model
  synthetic spectra are placed in fictitious binary systems and subjected
  to synthetic photometry processing. Techniques for photometric distance
  determination have been validated for all four photometric standards.

Title: Massive stars at low metallicity. Evolution and surface
    abundances of O dwarfs in the SMC
Authors: Bouret, J. -C.; Lanz, T.; Martins, F.; Marcolino, W. L. F.;
   Hillier, D. J.; Depagne, E.; Hubeny, I.
Bibcode: 2013A&A...555A...1B
Altcode: 2013arXiv1304.6923B
  <BR /> Aims: We aim to study the properties of massive stars at
  low metallicity, with an emphasis on their evolution, rotation, and
  surface abundances. We focus on O-type dwarfs in the Small Magellanic
  Cloud. These stars are expected to have weak winds that do not remove
  significant amounts of their initial angular momentum. <BR /> Methods:
  We analyzed the UV and optical spectra of twenty-three objects using
  the NLTE stellar atmosphere code cmfgen and derived photospheric and
  wind properties. <BR /> Results: The observed binary fraction of the
  sample is ≈26%, which is consistent with more systematic studies if
  one considers that the actual binary fraction is potentially larger
  owing to low-luminosity companions and that the sample was biased
  because it excluded obvious spectroscopic binaries. The location of
  the fastest rotators in the Hertzsprung-Russell (H-R) diagram built
  with fast-rotating evolutionary models and isochrones indicates that
  these could be several Myr old. The offset in the position of these
  fast rotators compared with the other stars confirms the predictions
  of evolutionary models that fast-rotating stars tend to evolve more
  vertically in the H-R diagram. Only one star of luminosity class
  Vz, expected to best characterize extreme youth, is located on the
  zero-age main sequence, the other two stars are more evolved. We
  found that the distribution of O and B stars in the ɛ(N) - vsin i
  diagram is the same, which suggests that the mechanisms responsible
  for the chemical enrichment of slowly rotating massive stars depend
  only weakly on the star's mass. We furthermore confirm that the group
  of slowly rotating N-rich stars is not reproduced by the evolutionary
  tracks. Even for more massive stars and faster rotators, our results
  call for stronger mixing in the models to explain the range of
  observed N abundances. All stars have an N/C ratio as a function of
  stellar luminosity that match the predictions of the stellar evolution
  models well. More massive stars have a higher N/C ratio than the less
  massive stars. Faster rotators show on average a higher N/C ratio
  than slower rotators, again consistent with the expected trend of
  stronger mixing as rotation increases. When comparing the N/O versus
  N/C ratios with those of stellar evolution models, the same global
  qualitative agreement is reached. The only discrepant behavior is
  observed for the youngest two stars of the sample, which both show
  very strong signs of mixing, which is unexpected for their evolutionary
  status. <P />Based on observations made with the NASA-ESA Hubble Space
  Telescope (program GO 11625), obtained at STScI, which is operated
  by AURA, Inc., under NASA contract NAS 5-26555. Based on observations
  collected at the European Southern Observatory Very Large Telescope,
  program 079.D-0073.Appendix B is available in electronic form at <A
  href="http://www.aanda.org">http://www.aanda.org</A>

Title: Chemical enrichment and physical conditions in I Zw 18
Authors: Lebouteiller, V.; Heap, S.; Hubeny, I.; Kunth, D.
Bibcode: 2013A&A...553A..16L
Altcode: 2013arXiv1302.4746L
  Context. Low-metallicity star-forming dwarf galaxies are prime targets
  to understand the chemical enrichment of the interstellar medium. The
  H i region contains the bulk of the mass in blue compact dwarfs, and
  it provides important constraints on the dispersal and mixing of heavy
  elements released by successive star-formation episodes. The metallicity
  of the H i region is also a critical parameter to investigate the future
  star-formation history, as metals provide most of the gas cooling that
  will facilitate and sustain star formation. <BR /> Aims: Our primary
  objective is to study the enrichment of the H i region and the interplay
  between star-formation history and metallicity evolution. Our secondary
  objective is to constrain the spatial- and time-scales over which the H
  i and H ii regions are enriched, and the mass range of stars responsible
  for the heavy element production. Finally, we aim to examine the gas
  heating and cooling mechanisms in the H i region. <BR /> Methods: We
  observed the most metal-poor star-forming galaxy in the Local Universe,
  I Zw 18, with the Cosmic Origin Spectrograph onboard Hubble. The
  abundances in the neutral gas are derived from far-ultraviolet
  absorption-lines (H i, C ii, C ii*, N i, O i, ...) and are compared to
  the abundances in the H ii region. Models are constructed to calculate
  the ionization structure and the thermal processes. We investigate the
  gas cooling in the H i region through physical diagnostics drawn from
  the fine-structure level of C<SUP>+</SUP>. <BR /> Results: We find that
  H i region abundances are lower by a factor of ~2 as compared to the H
  ii region. There is no differential depletion on dust between the H i
  and H ii region. Using sulfur as a metallicity tracer, we calculate a
  metallicity of 1/46 Z<SUB>⊙</SUB> (vs. 1/31 Z<SUB>⊙</SUB> in the
  H ii region). From the study of the C/O, [O/Fe], and N/O abundance
  ratios, we propose that C, N, O, and Fe are mainly produced in
  massive stars. We argue that the H i envelope may contain pockets of
  pristine gas with a metallicity essentially null. Finally, we derive
  the physical conditions in the H i region by investigating the C ii*
  absorption line. The cooling rate derived from C ii* is consistent
  with collisions with H<SUP>0</SUP> atoms in the diffuse neutral
  gas. We calculate the star-formation rate from the C ii* cooling rate
  assuming that photoelectric effect on dust is the dominant gas heating
  mechanism. Our determination is in good agreement with the values in
  the literature if we assume a low dust-to-gas ratio (~2000 times lower
  than the Milky Way value). <P />Appendix A is available in electronic
  form at <A href="http://www.aanda.org">http://www.aanda.org</A>

Title: 3D Spectral Radiative Transfer with IRIS: Application to
    the Simulation of Laboratory Models of Accretion Shocks in Young
    Stellar Objects
Authors: Ibgui, L.; Hubeny, I.; Lanz, T.; Stehlé, C.; González,
   M.; Chièze, J. P.
Bibcode: 2013ASPC..474...66I
Altcode:
  IRIS is a new three-dimensional radiative transfer code that provides
  spectroscopic diagnostics of hydrodynamics structures. We present its
  major numerical features and capabilities. We investigate the dynamical,
  radiative and spectral properties of laboratory generated radiative
  shocks, with the aim of improving our understanding of the mechanisms of
  accretion in young stellar objects. We employed IRIS to generate X-UV
  theoretical spectra, while three-dimensional non-stationary radiation
  hydrodynamics simulations were performed with the code HERACLES.

Title: Stellar Atmospheres
Authors: Hubeny, Ivan
Bibcode: 2013pss4.book...51H
Altcode:
  Basic concepts of the stellar atmospheres theory are briefly
  outlined. After discussing essential assumptions, approximations, and
  basic structural equations describing a stellar atmospheres, emphasis
  is given to describing efficient numerical methods developed to deal
  with the stellar atmosphere problem, namely the method of complete
  linearization and its recent variants, and the whole class of methods
  known by name Accelerated Lambda Iteration. The existing computer codes,
  and some of the most useful grids of model atmospheres that are publicly
  available, are briefly summarized. Some interesting properties of newly
  computed NLTE models atmospheres and their comparison to LTE models
  are shown. Finally, it is briefly shown how the model atmospheres are
  used to determine basic stellar parameters.

Title: IRIS: a generic three-dimensional radiative transfer code
Authors: Ibgui, L.; Hubeny, I.; Lanz, T.; Stehlé, C.
Bibcode: 2013A&A...549A.126I
Altcode: 2012arXiv1211.4870I
  Context. For most astronomical objects, radiation is the only probe of
  their physical properties. Therefore, it is important to have the most
  elaborate theoretical tool to interpret observed spectra or images,
  thus providing invaluable information to build theoretical models of
  the physical nature, the structure, and the evolution of the studied
  objects. <BR /> Aims: We present IRIS, a new generic three-dimensional
  (3D) spectral radiative transfer code that generates synthetic spectra,
  or images. It can be used as a diagnostic tool for comparison with
  astrophysical observations or laboratory astrophysics experiments. <BR
  /> Methods: We have developed a 3D short-characteristic solver that
  works with a 3D nonuniform Cartesian grid. We have implemented a
  piecewise cubic, locally monotonic, interpolation technique that
  dramatically reduces the numerical diffusion effect. The code takes
  into account the velocity gradient effect resulting in gradual Doppler
  shifts of photon frequencies and subsequent alterations of spectral
  line profiles. It can also handle periodic boundary conditions. This
  first version of the code assumes local thermodynamic equilibrium
  (LTE) and no scattering. The opacities and source functions are
  specified by the user. In the near future, the capabilities of IRIS
  will be extended to allow for non-LTE and scattering modeling. <BR />
  Results: IRIS has been validated through a number of tests. We provide
  the results for the most relevant ones, in particular a searchlight
  beam test, a comparison with a 1D plane-parallel model, and a test of
  the velocity gradient effect. <BR /> Conclusions: IRIS is a generic
  code to address a wide variety of astrophysical issues applied to
  different objects or structures, such as accretion shocks, jets in
  young stellar objects, stellar atmospheres, exoplanet atmospheres,
  accretion disks, rotating stellar winds, cosmological structures. It
  can also be applied to model laboratory astrophysics experiments,
  such as radiative shocks produced with high power lasers.

Title: Hydrodynamic modeling of accretion shocks on a star with
    radiative transport and a chromospheric model
Authors: de Sá, L.; Chièze, J. -P.; Stehlé, C.; Hubeny, I.;
   Delahaye, F.; Lanz, T.
Bibcode: 2012sf2a.conf..309D
Altcode:
  The aim of the project (ANR STARSHOCK) is to understand the dynamics
  and the radiative properties of accretion columns, linking the
  circumstellar disk to the surface photosphere of Young Stellar
  Objects. The hydrodynamics is computed first, using a high resolution
  hydrodynamic 1D ALE code (ASTROLABE) coupled to radiative transfer
  and line cooling, along with a model for the acoustic heating of
  the chromospheric plasma. Spectra are then post-processed with a 1D
  radiative transfer code (SYNSPEC), using DFE solver and an extended
  atomic database covering a wavelength range from X rays to visible.

Title: 3D numerical simulations of laboratory models of accretion
    shocks in young stellar objects
Authors: Ibgui, L.; Hubeny, I.; Lanz, T.; Stehlé, C.; González,
   M.; Chièze, J. -P.
Bibcode: 2012sf2a.conf..347I
Altcode:
  We show preliminary results of our numerical simulations of laboratory
  experiments of radiative shocks. Such experiments aim at understanding
  accretion shocks in young stellar objects. Three-dimensional
  non-stationary radiation hydrodynamics calculations were performed
  with the code HERACLES. X-UV spectra were then generated with the new
  three-dimensional radiative transfer code IRIS.

Title: An Online Catalog of Cataclysmic Variable Spectra from the
    Far-Ultraviolet Spectroscopic Explorer
Authors: Godon, Patrick; Sion, Edward M.; Levay, Karen; Linnell, Albert
   P.; Szkody, Paula; Barrett, Paul E.; Hubeny, Ivan; Blair, William P.
Bibcode: 2012ApJS..203...29G
Altcode: 2012arXiv1210.1118G
  We present an online catalog containing spectra and supporting
  information for cataclysmic variables that have been observed with
  the Far-Ultraviolet Spectroscopic Explorer (FUSE). For each object
  in the catalog we list some of the basic system parameters such as
  (R.A., decl.), period, inclination, and white dwarf mass, as well as
  information on the available FUSE spectra: data ID, observation date
  and time, and exposure time. In addition, we provide parameters needed
  for the analysis of the FUSE spectra such as the reddening E(B - V),
  distance, and state (high, low, intermediate) of the system at the time
  it was observed. For some of these spectra we have carried out model
  fits to the continuum with synthetic stellar and/or disk spectra using
  the codes TLUSTY and SYNSPEC. We provide the parameters obtained from
  these model fits; this includes the white dwarf temperature, gravity,
  projected rotational velocity, and elemental abundances of C, Si,
  S, and N, together with the disk mass accretion rate, the resulting
  inclination, and model-derived distance (when unknown). For each object
  one or more figures are provided (as gif files) with line identification
  and model fit(s) when available. The FUSE spectra and the synthetic
  spectra are directly available for download as ASCII tables. References
  are provided for each object, as well as for the model fits. In this
  article we present 36 objects, and additional ones will be added to
  the online catalog in the future. In addition to cataclysmic variables,
  we also include a few related objects, such as a wind-accreting white
  dwarf, a pre-cataclysmic variable, and some symbiotics.

Title: Modeling periodic media with the three-dimensional radiative
    transfer code IRIS
Authors: Ibgui, L.; Hubeny, I.; Lanz, T.; Stehlé, C.
Bibcode: 2012sf2a.conf..343I
Altcode:
  We describe the implementation in our generic three-dimensional
  radiative transfer code, IRIS, of an algorithm that allows the
  modeling of periodic infinite media. We show how this algorithm has
  been validated by comparison with well-established 1D plane-parallel
  models. A particularly interesting astrophysical application will be
  the calculation of synthetic spectra of the fully three-dimensional
  solar atmosphere.

Title: BINSYN: Simulating Spectra and Light Curves of Binary Systems
    with or without Accretion Disks
Authors: Linnell, Albert P.; DeStefano, Paul; Hubeny, Ivan
Bibcode: 2012ascl.soft08002L
Altcode:
  The BINSYN program suite is a collection of programs for analysis
  of binary star systems with or without an optically thick accretion
  disk. BINSYN produces synthetic spectra of individual binary star
  components plus a synthetic spectrum of the system. If the system
  includes an accretion disk, BINSYN also produces a separate synthetic
  spectrum of the disk face and rim. A system routine convolves the
  synthetic spectra with filter profiles of several photometric standards
  to produce absolute synthetic photometry output. The package generates
  synthetic light curves and determines an optimized solution for system
  parameters.

Title: BINSYN: A Publicly Available Program for Simulating Spectra
    and Light Curves of Binary Systems with or without Accretion Disks
Authors: Linnell, Albert P.; DeStefano, Paul; Hubeny, Ivan
Bibcode: 2012PASP..124..885L
Altcode:
  The BINSYN program suite, a collection of programs for analysis of
  binary star systems with or without an optically thick accretion disk,
  is available for download from a wiki. This article describes the
  package, including download instructions. BINSYN produces synthetic
  spectra of individual binary star components plus a synthetic spectrum
  of the system. If the system includes an accretion disk, BINSYN also
  produces a separate synthetic spectrum of the disk face and rim. A
  system routine convolves the synthetic spectra with filter profiles of
  several photometric standards to produce absolute synthetic photometry
  output. The package generates synthetic light curves and determines
  an optimized solution for system parameters. This article includes
  illustrative literature references that have used the suite, including
  mass transfer rates in several cataclysmic binary systems.

Title: Chemical abundances of hot post-AGB stars
Authors: Mello, D. R. C.; Daflon, S.; Pereira, C. B.; Hubeny, I.
Bibcode: 2012A&A...543A..11M
Altcode:
  Context. Hot post-AGB stars are luminous objects of low- and
  intermediate mass (0.8-8 M<SUB>⊙</SUB>) in the final stage
  of evolution, moving between the asymptotic giant branch (AGB)
  stars and planetary nebulae. The absorption lines observed in
  their spectra are typical of early-type stars and their abundance
  pattern may be associated with the occurence of one or more mixing
  processes during the previous AGB phase. <BR /> Aims: To better
  constrain their observed chemical pattern and evolutionary status,
  we determined chemical abundances for a sample of hot post-AGB
  stars selected according to spectroscopic criteria. <BR /> Methods:
  The observational data are high-resolution spectra obtained with the
  FEROS spectrograph. The stellar parameters and chemical composition
  were obtained from fully consistent non-LTE synthesis. <BR /> Results:
  The general abundance pattern reveals relevant nitrogen enrichment,
  slight depletion in carbon and sulfur and mild excess in helium
  for most of the objects. One notable exception is LSE 148, with Z =
  0.001, which is likely to be a metal-poor object at high galactic
  latitude. The atmospheric parameters and chemical abundances obtained
  are discussed in the context of evolutionary models. Mixing processes
  like the second/third dredged-up and "hot bottom-burning" are invoked to
  explain the obtained results. <P />Based on observations made with the
  2.2 m telescope at the European Southern Observatory (La Silla, Chile).

Title: From Interacting Binaries to Exoplanets: Essential Modeling
    Tools
Authors: Richards, Mercedes T.; Hubeny, Ivan
Bibcode: 2012IAUS..282.....R
Altcode:
  Preface; 1. Multiwavelength photometry and spectroscopy of interacting
  binaries; 2. Observations and analysis of exoplanets and brown dwarfs;
  3. Imaging techniques; 4. Model atmospheres of stars, interacting
  binaries, disks, exoplanets, and brown dwarfs; 5. Synthetic light
  curves and velocity curves, synthetic spectra of binary stars and their
  accretion; 6. Analysis of spectra and light curves; 7. Formation and
  evolution of binary stars, brown dwarfs, and planets; 8. Hydrodynamic
  simulations of exoplanets and mass transfer in interacting binaries;
  Summary; Index.

Title: From Interacting Binaries to Exoplanets (IAU S282)
Authors: Richards, Mercedes T.; Hubeny, Ivan
Bibcode: 2012fibe.book.....R
Altcode:
  Preface; 1. Multiwavelength photometry and spectroscopy of interacting
  binaries; 2. Observations and analysis of exoplanets and brown dwarfs;
  3. Imaging techniques; 4. Model atmospheres of stars, interacting
  binaries, disks, exoplanets, and brown dwarfs; 5. Synthetic light
  curves and velocity curves, synthetic spectra of binary stars and their
  accretion; 6. Analysis of spectra and light curves; 7. Formation and
  evolution of binary stars, brown dwarfs, and planets; 8. Hydrodynamic
  simulations of exoplanets and mass transfer in interacting binaries;
  Summary; Index.

Title: Modeling Atmospheres of Brown Dwarfs and Extrasolar Giant
    Planets
Authors: Hubeny, Ivan
Bibcode: 2012AAS...22041402H
Altcode:
  A brief review of spectroscopic studies of subsolar mass objects, namely
  brown dwarfs and extrasolar giant planets, is given, with emphasis on
  physics and chemistry of their atmospheres, their predicted spectra,
  and a comparison of theory with observations. Besides mentioning some
  recent highlights, main emphasis is given to discussing the role of
  uncertainties in the molecular opacity data, cloud formation physics,
  and departures from chemical equilibrium, on model atmospheres and
  theoretical spectra, and consequently on deducing basic physical
  properties of these objects.

Title: The distribution of metals in hot DA white dwarfs
Authors: Dickinson, N. J.; Barstow, M. A.; Hubeny, I.
Bibcode: 2012MNRAS.421.3222D
Altcode: 2012MNRAS.tmp.2468D; 2012arXiv1201.2940D
  The importance to stellar evolution of understanding the metal
  abundances in hot white dwarfs is well known. Previous work has
  found the hot DA white dwarfs REJ 1032+532, REJ 1614-085 and GD
  659 to have highly abundant, stratified photospheric nitrogen,
  due to the narrow absorption-line profiles of the far-ultraviolet
  (FUV) N V doublet and the lack of extreme-ultraviolet (EUV) continuum
  absorption. A preliminary analysis of the extremely narrow, deep line
  profiles of the photospheric metal absorption features of PG 0948+534
  suggested a similar photospheric metal configuration. However, other
  studies have found that REJ 1032+532, REJ 1614-085 and GD 659 can
  be well described by homogeneous models, with nitrogen abundances
  more in keeping with those of white dwarfs with higher effective
  temperatures. Here, a re-analysis of the nitrogen absorption features
  seen in REJ 1032+532, REJ 1614-085 and GD 659 is presented, with the
  aim of better understanding the structure of these stars, to test
  which models better represent the observed data and apply the results
  to the line profiles seen in PG 0948+534. A degeneracy is seen in the
  modelling of the nitrogen absorption-line profiles of REJ 1032+532,
  REJ 1614-085 and GD 659, with low-abundance, homogeneously distributed
  nitrogen models most likely being a better representation of the
  observed data. In PG 0948+534, no such degeneracy is seen, and the
  enigmatically deep line profiles could not be modelled satisfactorily.

Title: Panel Discussion III
Authors: Allard, F.; Batten, A.; Budding, E.; Devinney, E.; Eggleton,
   P.; Hatzes, A.; Hubeny, I.; Kley, W.; Lammer, H.; Linnell, A.; Trimble,
   V.; Wilson, R. E.
Bibcode: 2012IAUS..282..501A
Altcode:
  I. Hubeny Does anyone from the panel have a theme question to start with
  today? <P />V. Trimble It's another one-liner: From an active galaxy
  meeting many years ago when people talked about spiral structure. I
  was reminded by Dr. Rucinski's talk of Lodewijk Woltjer's remark:
  ``The larger our ignorance, the stronger the magnetic field.''

Title: Flash Mixing on the White Dwarf Cooling Curve: Spectroscopic
    Confirmation in NGC 2808
Authors: Brown, Thomas M.; Lanz, Thierry; Sweigart, Allen V.; Cracraft,
   Misty; Hubeny, Ivan; Landsman, Wayne B.
Bibcode: 2012ApJ...748...85B
Altcode: 2012arXiv1201.4070B
  We present new Hubble Space Telescope far-UV spectroscopy of two
  dozen hot evolved stars in NGC 2808, a massive globular cluster with
  a large population of "blue-hook" (BHk) stars. The BHk stars are
  found in ultraviolet color-magnitude diagrams of the most massive
  globular clusters, where they fall at luminosities immediately below
  the hot end of the horizontal branch (HB), in a region of the H-R
  diagram unexplained by canonical stellar evolution theory. Using
  new theoretical evolutionary and atmospheric models, we have shown
  that these subluminous HB stars are very likely the progeny of stars
  that undergo extensive internal mixing during a late He-core flash
  on the white dwarf cooling curve. This flash mixing leads to hotter
  temperatures and an enormous enhancement of the surface He and C
  abundances; these hotter temperatures, together with the decrease in H
  opacity shortward of the Lyman limit, make the BHk stars brighter in the
  extreme UV while appearing subluminous in the UV and optical. Our far-UV
  spectroscopy demonstrates that, relative to normal HB stars at the
  same color, the BHk stars of NGC 2808 are hotter and greatly enhanced
  in He and C, thus providing unambiguous evidence of flash mixing in
  the subluminous population. Although the C abundance in the BHk stars
  is orders of magnitude larger than that in the normal HB stars, the
  atmospheric C abundance in both the BHk and normal HB stars appears to
  be affected by gravitational settling. The abundance variations seen in
  Si and the Fe-peak elements also indicate that atmospheric diffusion is
  at play in our sample, with all of our hot subdwarfs at 25,000-50,000
  K exhibiting large enhancements of the iron-peak elements. The hottest
  subdwarfs in our BHk sample may be pulsators, given that they fall in
  the temperature range of newly discovered pulsating subdwarfs in ω
  Cen. In addition to the normal hot HB and BHk stars, we also obtain
  spectra of five blue HB stars, a post-HB star, and three unclassified
  stars with unusually blue UV colors. <P />Based on observations made
  with the NASA/ESA Hubble Space Telescope, obtained at STScI, which is
  operated by AURA, Inc., under NASA contract NAS 5-26555.

Title: Panel Discussion II
Authors: Allard, F.; Batten, A.; Budding, E.; Devinney, E.; Eggleton,
   P.; Hatzes, A.; Hubeny, I.; Kley, W.; Lammer, H.; Linnell, A.; Trimble,
   V.; Wilson, R. E.
Bibcode: 2012IAUS..282..341A
Altcode:
  I. Hubeny Today, the discussion will be open to the general audience. In
  Sessions C, D, and E, we have talked about models and modelling
  techniques so I expect the discussion will focus on these topics.

Title: Panel Discussion IV
Authors: Allard, F.; Batten, A.; Budding, E.; Devinney, E.; Eggleton,
   P.; Hatzes, A.; Hubeny, I.; Kley, W.; Lammer, H.; Linnell, A.; Trimble,
   V.; Wilson, R. E.
Bibcode: 2012IAUS..282..551A
Altcode:
  I. Hubeny Welcome to the last panel meeting. We invite general comments
  either from the audience or from the panelists. <P />V. Trimble Well,
  Mercedes started us with a vocabulary item and I think I would like to
  end with a vocabulary item. When they were first discovered, we called
  them `extra solar system planets' which was descriptive and fine,
  but it's just rather cumbersome. At some point they became `extra
  solar planets.' Now I have never seen a planet inside the Sun. And
  therefore `extrasolar' is not a good descriptor. `Exoplanets' is OK,
  but now that there are so many of them that perhaps they are simply
  `the planets.' When you want to specialize to ours, you could say
  `solar system planets.' Think how much ink it would save.

Title: Panel Discussion I
Authors: Allard, F.; Batten, A.; Budding, E.; Devinney, E.; Eggleton,
   P.; Hatzes, A.; Hubeny, I.; Kley, W.; Lammer, H.; Linnell, A.; Trimble,
   V.; Wilson, R. E.
Bibcode: 2012IAUS..282..145A
Altcode:
  M. Richards: Several talks today have expressed fuzzy boundaries to
  describe the objects called ``stars.'' Is the following classification
  correct? Are stars restricted to objects that have masses greater than
  0.089 solar masses and begin making energy with hydrogen burning? Do we
  include the stellar remnants: the white dwarfs and neturon stars? Do we
  include the brown dwarfs because they burn lithium or deuterium. We know
  that planets are not in this group since they have no energy production.

Title: Basic Tools for Modeling Stellar and Planetary Atmospheres
Authors: Hubeny, Ivan
Bibcode: 2012IAUS..282..221H
Altcode:
  Most popular computer codes for calculating model stellar and planetary
  atmospheres are briefly reviewed. A particular emphasis is devoted to
  our universal computer program Tlusty (model stellar atmospheres and
  accretion disks), CoolTlusty (a variant of Tlusty for computing model
  atmospheres of substellar-mass objects such as giant planets and brown
  dwarfs), and Synspec (an associated spectrum synthesis code). We show
  the highlights of actual applications of these codes which include
  extensive grids of fully line-blanketed non-LTE model atmospheres
  of O and B stars, and grids of model atmospheres of extrasolar giant
  planets and L and T dwarfs.

Title: Day-Night Side Cooling of a Strongly Irradiated Giant Planet
Authors: Budaj, Ján; Burrows, Adam; Hubeny, Ivan
Bibcode: 2012IAUS..282..486B
Altcode:
  The internal heat loss or cooling of a planet determines its structure
  and evolution. We address in a consistent fashion the coupling between
  the day and the night sides by means of model atmosphere calculations
  with heat redistribution. We assume that a strong convection leads to
  the same entropy on the day and night side and that the gravity is the
  same on both hemispheres. We argue that the core cooling rate from the
  two hemispheres of a strongly irradiated planet may not be the same
  and that the difference depends on several important parameters. If the
  day-night heat redistribution is very effective, or if it takes place
  at a large optical depth, then the day-side and the night-side cooling
  may be comparable. However, if the day-night heat transport is not
  effective, or if it takes place at a shallow optical depth, then there
  can be a big difference between the day-side and the night-side cooling
  and the night side may cool more effectively. If the stellar irradiation
  gets stronger e.g. due to the stellar evolution or migration, this will
  reduce both the day and the night side cooling. Enhanced metallicity
  in the atmosphere acts as a ``blanket'' and reduces both the day- and
  the night-side cooling. However, the stratosphere on the day side of
  the planet can enhance the day-side cooling since its opacity acts as a
  ``shield'' which screens the stellar irradiation. These results might
  affect the well known gravity darkening and bolometric albedo effects in
  interacting binaries, especially for strongly irradiated cold objects.

Title: New Observational Evidence of Flash Mixing on the White Dwarf
    Cooling Curve
Authors: Brown, T. M.; Lanz, T.; Sweigart, A. V.; Cracraft, M.;
   Hubeny, I.; Landsman, W. B.
Bibcode: 2012ASPC..452...23B
Altcode: 2012arXiv1201.4204B
  Blue hook stars are a class of subluminous extreme horizontal branch
  stars that were discovered in UV images of the massive globular clusters
  ω Cen and NGC 2808. These stars occupy a region of the HR diagram
  that is unexplained by canonical stellar evolution theory. Using
  new theoretical evolutionary and atmospheric models, we have shown
  that the blue hook stars are very likely the progeny of stars that
  undergo extensive internal mixing during a late helium-core flash
  on the white dwarf cooling curve. This “flash mixing” produces
  hotter-than-normal EHB stars with atmospheres significantly enhanced
  in helium and carbon. The larger bolometric correction, combined with
  the decrease in hydrogen opacity, makes these stars appear subluminous
  in the optical and UV. Flash mixing is more likely to occur in stars
  born with a high helium abundance, due to their lower mass at the
  main sequence turnoff. For this reason, the phenomenon is more common
  in those massive globular clusters that show evidence for secondary
  populations enhanced in helium. However, a high helium abundance does
  not, by itself, explain the presence of blue hook stars in massive
  globular clusters. Here, we present new observational evidence for flash
  mixing, using recent HST observations. These include UV color-magnitude
  diagrams of six massive globular clusters and far-UV spectroscopy of
  hot subdwarfs in one of these clusters (NGC 2808).

Title: 3D modeling of accretion shocks in young stellar objects :
    Simulation of laboratory experiments
Authors: Ibgui, L.; González, M.; Stehlé, C.; Hubeny, I.; Lanz, T.
Bibcode: 2012EAS....58..149I
Altcode:
  In order to improve the understanding of the physics of accretion shocks
  around young stellar objects, we have performed a three dimensional
  simulation of a radiative shock generated in a laser installation. We
  depict the 3D structure of such a shock. Radiation hydrodynamics is
  modeled with the HERACLES code; then, radiative transfer post-processing
  is performed with the IRIS code.

Title: Chemical homogeneity in the Orion Association: Oxygen
    abundances of B stars
Authors: Cunha, K.; Hubeny, I.; Lanz, T.
Bibcode: 2012EPJWC..1908005C
Altcode: 2011arXiv1110.5879C
  We present non-LTE oxygen abundances for a sample of B stars in the
  Orion association. The abundance calculations included non-LTE line
  formation and used fully blanketed non-LTE model atmospheres. The
  stellar parameters were the same as adopted in the previous study by
  Cunha &amp; Lambert (1994). We find that the young Orion stars in
  this sample of 10 stars are described by a single oxygen abundance
  with an average value of A(O) = 8.78 and a small dispersion of ±0.05,
  dex which is of the order of the uncertainties in the analysis. This
  average oxygen abundance compares well with the average oxygen
  abundance obtained previously in Cunha &amp; Lambert (1994): A(O) =
  8.72 ± 0.13 although this earlier study, based upon non-blanketed
  model atmospheres in LTE, displayed larger scatter. Small scatter
  of chemical abundances in Orion B stars had also been found in our
  previous studies for neon and argon; all based on the same effective
  temperature scale. The derived oxygen abundance distribution for the
  Orion association compares well with other results for the oxygen
  abundance in the solar neighborhood.

Title: Day and night side core cooling of a strongly irradiated
    giant planet
Authors: Budaj, J.; Hubeny, I.; Burrows, A.
Bibcode: 2012A&A...537A.115B
Altcode: 2011arXiv1111.5478B
  Context. The internal heat loss, or cooling, of a planet determines
  its structure and evolution. <BR /> Aims: We study the effects of
  irradiation, metallicity of the atmosphere, heat redistribution,
  stratospheres, and the depth where the heat redistribution takes place
  on the atmospheric structure, the core entropy, and subsequently on
  the cooling of the interior of the planet. <BR /> Methods: We address
  in a consistent fashion the coupling between the day and the night
  sides of a planet by means of model atmosphere calculations with heat
  redistribution. We assume that strong convection leads to the same
  entropy on the day and night sides and that gravity is the same on both
  hemispheres. <BR /> Results: We argue that the core cooling rates from
  the two hemispheres of a strongly irradiated planet may not be the same
  and that the difference depends on several important parameters. If the
  day-night heat redistribution is very efficient or if it takes place at
  the large optical depth, then the day-side and the night-side cooling
  may be comparable. However, if the day-night heat transport is not
  efficient or if it takes place at a shallow optical depth then there
  can be a large difference between the day- and the night-side cooling
  and the night side will cool more efficiently. If stellar irradiation
  becomes stronger, e.g. owing to stellar evolution or migration, cooling
  from both the day and the night sides is reduced. Enhanced metallicity
  of the atmosphere would act as an added "blanket" and reduces both
  the day- and the night-side cooling. However, a stratosphere on the
  planetary day side can enhance day-side cooling since its opacity acts
  as a "sunshade" that screens the stellar irradiation. These effects may
  also influence the well-known gravity darkening and bolometric albedo
  effects in interacting binaries, especially for strongly irradiated
  cold components.

Title: SPEC3D: a three-dimensional radiative transfer code for
    astrophysical and laboratory applications
Authors: Ibgui, L.; Hubeny, I.; Lanz, T.; Stehlé, C.
Bibcode: 2011sf2a.conf..485I
Altcode:
  We have developed a generic three-dimensional radiative transfer code,
  SPEC3D, aimed at post-processing 3D radiation magnetohydrodynamics
  simulations. SPEC3D solves the monochromatic 3D radiative transfer
  equation. The numerical approach and the major features of the
  code are presented. The wide range of applications includes the
  modeling of a number of astrophysical objects and structures,
  such as accretion shocks around young stellar objects, stellar and
  exoplanets atmospheres, cosmological structures, but also the modeling
  of laboratory astrophysics experiments such as magnetohydrodynamics
  jets and radiative shocks.

Title: Synspec: General Spectrum Synthesis Program
Authors: Hubeny, Ivan; Lanz, Thierry
Bibcode: 2011ascl.soft09022H
Altcode:
  Synspec is a user-oriented package written in FORTRAN for modeling
  stellar atmospheres and for stellar spectroscopic diagnostics. It
  assumes an existing model atmosphere, calculated previously with Tlusty
  or taken from the literature (for instance, from the Kurucz grid of
  models). The opacity sources (continua, atomic and molecular lines)
  are fully specified by the user. An arbitrary stellar rotation and
  instrumental profile can be applied to the synthetic spectrum.

Title: TLUSTY: Stellar Atmospheres, Accretion Disks, and Spectroscopic
    Diagnostics
Authors: Hubeny, Ivan; Lanz, Thierry
Bibcode: 2011ascl.soft09021H
Altcode:
  TLUSTY is a user-oriented package written in FORTRAN77 for modeling
  stellar atmospheres and accretion disks and wide range of spectroscopic
  diagnostics. In the program's maximum configuration, the user may start
  from scratch and calculate a model atmosphere of a chosen degree of
  complexity, and end with a synthetic spectrum in a wavelength region of
  interest for an arbitrary stellar rotation and an arbitrary instrumental
  profile. The user may also model the vertical structure of annuli of
  an accretion disk.

Title: A Method for the Study of Accretion Disk Emission in
    Cataclysmic Variables. I. The Model
Authors: Puebla, Raúl E.; Diaz, Marcos P.; Hillier, D. John;
   Hubeny, Ivan
Bibcode: 2011ApJ...736...17P
Altcode: 2011arXiv1105.0851P
  We have developed a spectrum synthesis method for modeling the
  ultraviolet (UV) emission from the accretion disk from cataclysmic
  variables (CVs). The disk is separated into concentric rings, with
  an internal structure from the Wade &amp; Hubeny disk-atmosphere
  models. For each ring, a wind atmosphere is calculated in the comoving
  frame with a vertical velocity structure obtained from a solution of
  the Euler equation. Using simple assumptions, regarding rotation and
  the wind streamlines, these one-dimensional models are combined into a
  single 2.5-dimensional model for which we compute synthetic spectra. We
  find that the resulting line and continuum behavior as a function
  of the orbital inclination is consistent with the observations, and
  verify that the accretion rate affects the wind temperature, leading
  to corresponding trends in the intensity of UV lines. In general,
  we also find that the primary mass has a strong effect on the P Cygni
  absorption profiles, the synthetic emission line profiles are strongly
  sensitive to the wind temperature structure, and an increase in the
  mass-loss rate enhances the resonance line intensities. Synthetic
  spectra were compared with UV data for two high orbital inclination
  nova-like CVs—RW Tri and V347 Pup. We needed to include disk regions
  with arbitrary enhanced mass loss to reproduce reasonably well widths
  and line profiles. This fact and a lack of flux in some high ionization
  lines may be the signature of the presence of density-enhanced regions
  in the wind, or alternatively, may result from inadequacies in some
  of our simplifying assumptions.

Title: An Improved Tlusty Model Of Cataclysmic Variable Accretion
    Disk Annuli.
Authors: Linnell, Albert P.; Hubeny, I.
Bibcode: 2011AAS...21821905L
Altcode: 2011BAAS..43G21905L
  The Hubeny TLUSTY and SYNSPEC programs have been used in several
  studies of Nova-like Cataclysmic Variable stars, especially models of
  their accretion disks. Tabulations of column masses for the individual
  annuli (which are always optically thick) listed values in disagreement
  with theoretical models in the literature (e.g., Lasota, 2001, NAR,
  45, 449, Fig. 1). The discrepancy arose from an inadequate treatment
  of convection in TLUSTY (which had been developed with particular
  attention to radiation-dominated accretion disks). A new version of
  TLUSTY, developed by Hubeny, corrects the discrepancy and produces
  an insignificant change in our published conclusions. We illustrate
  the results for our study of RW Sextantis (Linnell et al., 2010,
  ApJ,719,271).

Title: The Hot Components of AM CVn Helium Cataclysmics
Authors: Sion, Edward M.; Linnell, A. P.; Godon, P.; Hubeny, I.
Bibcode: 2011AAS...21733805S
Altcode: 2011BAAS...4333805S
  The AM CVn helium-transfer cataclysmic variables are fundametally
  important because they are the progeny of double common envelope
  evolution, they are a principal source of low frequency gravitational
  wave emission, a laboratory for accretion and interior physics under
  extreme conditions and candidates for Type Ia supernovae. The hot
  component, consisting of a helium-rich white dwarf and disk, is
  the focus of our synthetic spectral analysis using the code BINSYN
  (Linnell&amp; Hubeny 1996) which takes into account the donor companion
  star, the shock front which forms at the disk edge and the FUV and
  NUV energy distribution. <P />We report the first results from our
  multi-component study of helium accretion and white dwarf heating. <P
  />This research was supported by NASA ADP grant NN09AC94G and in part
  by NSF grant AST0807892, both to Villanova University.

Title: Discovery of a New AM CVn System with the Kepler Satellite
Authors: Fontaine, G.; Brassard, P.; Green, E. M.; Charpinet, S.;
   Dufour, P.; Hubeny, I.; Steeghs, D.; Aerts, C.; Randall, S. K.;
   Bergeron, P.; Guvenen, B.; O'Malley, C. J.; Van Grootel, V.; Østensen,
   R. H.; Bloemen, S.; Silvotti, R.; Howell, S. B.; Baran, A.; Kepler,
   S. O.; Marsh, T. R.; Montgomery, M. H.; Oreiro, R.; Provencal, J.;
   Telting, J.; Winget, D. E.; Zima, W.; Christensen-Dalsgaard, J.;
   Kjeldsen, H.
Bibcode: 2011ApJ...726...92F
Altcode:
  We report the discovery of a new AM CVn system on the basis of
  broadband photometry obtained with the Kepler satellite supplemented
  by ground-based optical spectroscopy. Initially retained on Kepler
  target lists as a potential compact pulsator, the blue object SDSS
  J190817.07+394036.4 (KIC 004547333) has turned out to be a high-state
  AM CVn star showing the He-dominated spectrum of its accretion disk
  significantly reddened by interstellar absorption. We constructed
  new grids of NLTE synthetic spectra for accretion disks in order to
  analyze our spectroscopic observations. From this analysis, we infer
  preliminary estimates of the rate of mass transfer, the inclination
  angle of the disk, and the distance to the system. The AM CVn nature
  of the system is also evident in the Kepler light curve, from which
  we extracted 11 secure periodicities. The luminosity variations are
  dominated by a basic periodicity of 938.507 s, likely to correspond to a
  superhump modulation. The light curve folded on the period of 938.507 s
  exhibits a pulse shape that is very similar to the superhump wavefront
  seen in AM CVn itself, which is a high-state system and the prototype
  of the class. Our Fourier analysis also suggests the likely presence
  of a quasi-periodic oscillation similar to those already observed in
  some high-state AM CVn systems. Furthermore, some very low-frequency,
  low-amplitude aperiodic photometric activity is likely present, which
  is in line with what is expected in accreting binary systems. Inspired
  by previous work, we further looked for and found some intriguing
  numerical relationships between the 11 secure detected frequencies,
  in the sense that we can account for all of them in terms of only
  three basic clocks. This is further evidence in favor of the AM CVn
  nature of the system.

Title: Hot, Massive Stars in I Zw 18
Authors: Heap, Sara R.; Hubeny, Ivan; Lanz, Thierry; Landsman, Wayne;
   Lindler, Don; Malumuth, Eliot
Bibcode: 2011BSRSL..80..149H
Altcode:
  We present the far-ultraviolet spectrum of the northwest component of I
  Zw 18, a blue compact galaxy having a very low metallicity. The spectrum
  is compatible with continuous star-formation over the past ∼ 15 Myr
  (CSF age), and a very low metallicity, log Z/Z_⊙ ∼ -1.7, although
  the stellar surface may be enhanced in carbon. Stellar winds are very
  weak, and the edge velocity of wind lines is very low (∼ 250 km/s).

Title: The Anomalous Accretion Disk of the Cataclysmic Variable
    RW Sextantis
Authors: Linnell, Albert P.; Godon, P.; Hubeny, I.; Sion, E. M.;
   Szkody, P.
Bibcode: 2011AAS...21733804L
Altcode: 2011BAAS...4333804L
  The standard model for stable Cataclysmic Variable (CV) accretion disks
  (Frank, King and Raine 1992) derives an explicit analytic expression for
  the disk effective temperature as function of radial distance from the
  white dwarf (WD). That model specifies that the effective temperature,
  Teff(R), varies with R as ()<SUP>0.25</SUP>, where () represents a
  combination of parameters including R, the mass transfer rate M(dot),
  and other parameters. It is well known that fits of standard model
  synthetic spectra to observed CV spectra find almost no instances of
  agreement. We have derived a generalized expression for the radial
  temperature gradient, which preserves the total disk luminosity as
  function of M(dot) but permits a different exponent from the theoretical
  value of 0.25, and have applied it to RW Sex (Linnell et al.,2010,ApJ,
  719,271). We find an excellent fit to observed FUSE and IUE spectra for
  an exponent of 0.125, curiously close to 1/2 the theoretical value. Our
  annulus synthetic spectra, combined to represent the accretion disk,
  were produced with program TLUSTY, were non-LTE and included H, He, C,
  Mg, Al, Si, and Fe as explicit ions. We illustrate our results with a
  plot showing the failure to fit RW Sex for a range of M(dot) values,
  our model fit to the observations, and a chi<SUP>2</SUP> plot showing
  the selection of the exponent 0.125 as the best fit for the M(dot)
  range shown. (For the final model parameters see the paper cited.)

Title: HST/WFC3 Photometry of NGC 2808 and Its Multiple Main Sequences
Authors: Jeffery, Elizabeth; Brown, T.; Dotter, A.; Hubeny, I.;
   Landsman, W. B.; Lanz, T.; Sweigart, A. V.
Bibcode: 2011AAS...21715212J
Altcode: 2011BAAS...4315212J
  Recent high precision photometric observations of several globular
  clusters have revealed that these simple stellar populations may not
  be as simple as we once believed. Some globular clusters have shown
  interesting features in their color-magnitude diagrams indicating
  the presence of multiple populations. Recent HST observations of the
  massive globular cluster NGC 2808 have revealed the presence of three
  main sequences. We present new observations of NGC 2808 using the
  new WFC3 camera on HST. Observations are in five photometric bands
  covering a large wavelength range from the UVIS to the IR channels
  of WFC3. Moreover, these observations extend below the "turn down"
  in the lower main sequence (as seen in the IR CMD) and therefore reach
  deeper than past data sets on this cluster. We discuss various model
  fits and compare with other observed CMDs of other globular clusters
  to explore the origin of these multiple sequences.

Title: The Stratification of Metals in Hot White Dwarf Atmospheres
Authors: Dickinson, N. J.; Barstow, M. A.; Hubeny, I.
Bibcode: 2010AIPC.1273..400D
Altcode:
  The atmospheres of many hot white dwarfs contain significant quantities
  of metals. Various studies have reached different conclusions on the
  distribution of nitrogen in the atmosphere of REJ1032+532, a 44,350 K
  DA. Here, we examine this object again to gain a better understanding
  of its nitrogen distribution, and attempt to model the C IV features
  seen in the DA PG0948+534 (110,0000 K).

Title: Non-LTE Models and Theoretical Spectra of Accretion Disks in
    Active Galactic Nuclei. III. Integrated Spectra for Hydrogen-Helium
    Disks
Authors: Hubeny, Ivan; Agol, Eric; Blaes, Omer; Krolik, Julian
Bibcode: 2010ascl.soft11016H
Altcode:
  We have constructed a grid of non-LTE disk models for a wide range
  of black hole mass and mass accretion rate, for several values of
  viscosity parameter alpha, and for two extreme values of the black
  hole spin: the maximum-rotation Kerr black hole, and the Schwarzschild
  (non-rotating) black hole. Our procedure calculates self-consistently
  the vertical structure of all disk annuli together with the radiation
  field, without any approximations imposed on the optical thickness
  of the disk, and without any ad hoc approximations to the behavior of
  the radiation intensity. The total spectrum of a disk is computed by
  summing the spectra of the individual annuli, taking into account the
  general relativistic transfer function. The grid covers nine values of
  the black hole mass between M = 1/8 and 32 billion solar masses with
  a two-fold increase of mass for each subsequent value; and eleven
  values of the mass accretion rate, each a power of 2 times 1 solar
  mass/year. The highest value of the accretion rate corresponds to 0.3
  Eddington. We show the vertical structure of individual annuli within
  the set of accretion disk models, along with their local emergent flux,
  and discuss the internal physical self-consistency of the models. We
  then present the full disk-integrated spectra, and discuss a number
  of observationally interesting properties of the models, such as
  optical/ultraviolet colors, the behavior of the hydrogen Lyman limit
  region, polarization, and number of ionizing photons. Our calculations
  are far from definitive in terms of the input physics, but generally
  we find that our models exhibit rather red optical/UV colors. Flux
  discontinuities in the region of the hydrogen Lyman limit are only
  present in cool, low luminosity models, while hotter models exhibit
  blueshifted changes in spectral slope.

Title: Theory and modeling of stellar atmospheres
Authors: Hubeny, Ivan
Bibcode: 2010AIPC.1268...73H
Altcode:
  I will briefly outline basic concepts of the stellar atmospheres
  theory. After summarizing basic structural equations describing a
  stellar atmospheres, an emphasis is given to describing efficient
  numerical methods developed to deal with the stellar atmosphere problem,
  namely the method of complete linearization ant its recent variants,
  and the whole class of methods known by name Accelerated Lambda
  Iteration. In the next part of the lectures I will briefly summarize
  existing computer codes, with an emphasis on our code TLUSTY, and list
  some of the most useful grids of model atmospheres that are publicly
  available. Next, I will show how the model atmospheres and synthetic
  spectra are used in quantitative stellar spectroscopy in order to
  determine basic stellar parameters and chemical abundances. Finally,
  I will briefly describe an application of model atmosphere theory
  and models to related objects, such as accretion disks around various
  accretors, and atmospheres of substellar-mass objects-extrasolar giant
  planets and brown dwarfs.

Title: The Anomalous Accretion Disk of the Cataclysmic Variable
    RW Sextantis
Authors: Linnell, Albert P.; Godon, Patrick; Hubeny, Ivan; Sion,
   Edward M.; Szkody, Paula
Bibcode: 2010ApJ...719..271L
Altcode: 2010arXiv1006.2832L
  Synthetic spectra covering the wavelength range 900-3000 Å provide an
  accurate fit, established by a χ<SUP>2</SUP> <SUB>ν</SUB> analysis, to
  a combined observed spectrum of RW Sextantis. Two separately calibrated
  distances to the system establish the synthetic spectrum comparison
  on an absolute flux basis but with two alternative scaling factors,
  requiring alternative values of \dot{M} for final models. Based on
  comparisons for a range of \dot{M} values, the observed spectrum
  does not follow the standard model. Rather than the exponent 0.25
  in the expression for the radial temperature profile, a value close
  to 0.125 produces a synthetic spectrum with an accurate fit to the
  combined spectrum. A study of time-series Far Ultraviolet Spectroscopic
  Explorer spectra shows that a proposed warped or tilted disk is not
  supported by the data; an alternative proposal is that an observed
  non-axisymmetric wind results from an interaction with the mass transfer
  stream debris. <P />Based on observations made with the NASA/ESA Hubble
  Space Telescope, obtained at the Space Telescope Science Institute,
  which is operated by the Association of Universities for Research in
  Astronomy, Inc. under NASA contract NAS5-26555, and the NASA-CNES-CSA
  Far Ultraviolet Explorer, which is operated for NASA by the Johns
  Hopkins University under NASA contract NAS5-32985.

Title: The Blue Hook Populations of Massive Globular Clusters
Authors: Brown, Thomas M.; Sweigart, Allen V.; Lanz, Thierry; Smith,
   Ed; Landsman, Wayne B.; Hubeny, Ivan
Bibcode: 2010ApJ...718.1332B
Altcode: 2010arXiv1006.1591B
  We present new Hubble Space Telescope ultraviolet color-magnitude
  diagrams of five massive Galactic globular clusters: NGC 2419, NGC 6273,
  NGC 6715, NGC 6388, and NGC 6441. These observations were obtained to
  investigate the "blue hook" (BH) phenomenon previously observed in UV
  images of the globular clusters ω Cen and NGC 2808. Blue hook stars are
  a class of hot (approximately 35,000 K) subluminous horizontal branch
  stars that occupy a region of the HR diagram that is unexplained by
  canonical stellar evolution theory. By coupling new stellar evolution
  models to appropriate non-LTE synthetic spectra, we investigate various
  theoretical explanations for these stars. Specifically, we compare our
  photometry to canonical models at standard cluster abundances, canonical
  models with enhanced helium (consistent with cluster self-enrichment
  at early times), and flash-mixed models formed via a late helium-core
  flash on the white dwarf cooling curve. We find that flash-mixed models
  are required to explain the faint luminosity of the BH stars, although
  neither the canonical models nor the flash-mixed models can explain the
  range of color observed in such stars, especially those in the most
  metal-rich clusters. Aside from the variation in the color range, no
  clear trends emerge in the morphology of the BH population with respect
  to metallicity. <P />Based on observations made with the NASA/ESA Hubble
  Space Telescope, obtained at STScI, and associated with proposal 10815.

Title: Commission 36: Theory of Stellar Atmospheres
Authors: Asplund, Martin; Puls, Joachim; Landstreet, John; Allende
   Prieto, Carlos; Ayres, Thomas; Berdyugina, Svetlana; Gustafsson,
   Bengt; Hubeny, Ivan; Ludwig, Hans Günter; Mashonkina, Lyudmila;
   Randich, Sofia
Bibcode: 2010IAUTB..27..197A
Altcode:
  The members of the Commission 36 Organizing Committee attending the IAU
  General Assembly in Rio de Janeiro met for a business session on August
  7. Both members from the previous (2006-2009) and the new (2009-2012)
  Organizing Committee partook in the discussions. Past president John
  Landstreet described the work he had done over the past three years
  in terms of supporting proposed conferences on the topic. He has
  also spent significant amount of time establishing an updated mailing
  list of all &gt;350 members of the commission, which is unfortunately
  not provided automatically by the IAU. Such a list is critical for a
  rapid dissemination of information to the commission members and for
  a correct and smooth running of elections of IAU officials. Everyone
  present thanked John effusively for all of his hard work over the past
  three years to stimulate a high level of activity within the discipline.

Title: The Determination of the Abundances of the Fe Group Elements
    in Early B Stars from High Resolution FUV Spectra
Authors: Peters, Geraldine J.; Adelman, Saul J.; Hubeny, Ivan;
   Lanz, Thierry
Bibcode: 2010IAUS..265..213P
Altcode:
  We present selected results from an investigation that is currently
  underway to determine the abundances of the Fe group elements in early
  B stars and assess the extent to which contemporary NLTE and LTE models
  represent their atmospheres. High resolution UV and optical spectra of
  B stars that display ultrasharp lines are compared with computations
  from TLUSTY/SYNSPEC and SYNTHE. Some results from our analysis of the
  abundance standard ι Her (B3V) are presented here.

Title: The Blue Hook Populations of Massive Globular Clusters
Authors: Brown, Thomas M.; Sweigart, A. V.; Lanz, T.; Smith, E.;
   Landsman, W. B.; Hubeny, I.
Bibcode: 2010AAS...21542516B
Altcode: 2010BAAS...42..338B
  We present new HST ultraviolet color-magnitude diagrams of 5 massive
  Galactic globular clusters: NGC 2419, NGC 6273, NGC 6715, NGC 6388,
  and NGC 6441. &amp;nbspThese observations were obtained in order
  to investigate the "blue hook" phenomenon previously observed in
  HST ultraviolet images of the globular clusters omega Cen and NGC
  2808. &amp;nbspBlue hook stars are a class of hot (approximately
  35,000 K) subluminous horizontal branch stars that occupy a
  region of the HR diagram that is unexplained by canonical stellar
  evolution theory. &amp;nbspBy coupling new stellar evolution models
  to appropriate non-LTE synthetic spectra, we investigate various
  theoretical explanations for these stars. &amp;nbspSpecifically, we
  compare the color-magnitude diagrams to stellar models that assume
  normal evolution at cluster abundances, models with enhanced helium
  resulting from cluster self-enrichment, and flash-mixed models formed
  via late helium core flash on the white dwarf cooling curve.

Title: Models of Neptune-Mass Exoplanets: Emergent Fluxes and Albedos
Authors: Spiegel, David S.; Burrows, Adam; Ibgui, Laurent; Hubeny,
   Ivan; Milsom, John A.
Bibcode: 2010ApJ...709..149S
Altcode: 2009arXiv0909.2043S
  There are now many known exoplanets with Msin i within a factor
  of 2 of Neptune's, including the transiting planets GJ 436b and
  HAT-P-11b. Planets in this mass range are different from their more
  massive cousins in several ways that are relevant to their radiative
  properties and thermal structures. By analogy with Neptune and Uranus,
  they are likely to have metal abundances that are an order of magnitude
  or more greater than those of larger, more massive planets. This
  increases their opacity, decreases Rayleigh scattering, and changes
  their equation of state. Furthermore, their smaller radii mean that
  fluxes from these planets are roughly an order of magnitude lower than
  those of otherwise identical gas giant planets. Here, we compute a range
  of plausible radiative equilibrium models of GJ 436b and HAT-P-11b. In
  addition, we explore the dependence of generic Neptune-mass planets on
  a range of physical properties, including their distance from their
  host stars, their metallicity, the spectral type of their stars, the
  redistribution of heat in their atmospheres, and the possible presence
  of additional optical opacity in their upper atmospheres.

Title: Quantitative Analysis of the Spectra of Early B Stars with
    Ultrasharp Lines
Authors: Peters, Geraldine J.; Adelman, S.; Hubeny, I.; Lanz, T.
Bibcode: 2009AAS...21460512P
Altcode:
  The extent to which contemporary NLTE and LTE models represent
  the atmospheres of the early B stars with the sharpest lines is
  discussed. Due to the low rotational broadening in these stars, line
  blending presents minimal problems and the intrinsic line profiles are
  revealed. Spectral data from the HST and FUSE spacecraft and the KPNO
  Coude Feed Telescope are compared with computations from the Hubeny/Lanz
  codes TLUSTY/SYNSPEC and the Kurucz code SYNTHE. The B stars include
  ι Her (B3V), HR 1886 (B1V), HR 1887 (B0.5V), and AV 304 (B0.5V) in the
  SMC, all of which are considered to be abundance standards. Contemporary
  NLTE model atmospheres represent the photospheres of early B stars
  remarkably well. Some lines are fit much better in NLTE even for the B3
  stars, but widespread discrepancies seem to emerge for stars hotter than
  B0.5, which also show dynamic atmospheres. Future work need to be done
  on the following: 1) The determination and meaning of microturbulence
  and its effect on the atmosphere, 2) Further attention to the strong
  Si II lines, especially Multiplet 4, 3) Treatment of Ti, V, Cr, Mn,
  Co, and Ni in NLTE, 4) Wind models for B0-B0.5 stars. <P />The authors
  appreciate support from NASA grants NAG5-11802, NAG5-12239, NAG5-13212,
  and STScI grants GO-09848 &amp; GO-06709.

Title: V3885 Sagittarius: A Comparison with a Range of Standard
    Model Accretion Disks
Authors: Linnell, Albert P.; Godon, Patrick; Hubeny, Ivan; Sion,
   Edward M.; Szkody, Paula; Barrett, Paul E.
Bibcode: 2009ApJ...703.1839L
Altcode: 2009arXiv0908.1525L
  A \widetilde{χ}^2 analysis of standard model accretion disk synthetic
  spectrum fits to combined Far Ultraviolet Spectroscopic Explorer and
  Space Telescope Imaging Spectrograph spectra of V3885 Sagittarius, on
  an absolute flux basis, selects a model that accurately represents the
  observed spectral energy distribution. Calculation of the synthetic
  spectrum requires the following system parameters. The cataclysmic
  variable secondary star period-mass relation calibrated by Knigge in
  2006 and 2007 sets the secondary component mass. A mean white dwarf (WD)
  mass from the same study, which is consistent with an observationally
  determined mass ratio, sets the adopted WD mass of 0.7 M <SUB>sun</SUB>,
  and the WD radius follows from standard theoretical models. The adopted
  inclination, i = 65°, is a literature consensus, and is subsequently
  supported by \widetilde{χ}^2 analysis. The mass transfer rate is the
  remaining parameter to set the accretion disk T <SUB>eff</SUB> profile,
  and the Hipparcos parallax constrains that parameter to \dot{M}=(5.0±
  2.0)× 10^{-9} M_{⊙} yr^{-1} by a comparison with observed
  spectra. The fit to the observed spectra adopts the contribution of
  a 57, 000 ± 5000 K WD. The model thus provides realistic constraints
  on \dot{M} and T <SUB>eff</SUB> for a large \dot{M} system above the
  period gap. <P />Based on observations made with the NASA/ESA Hubble
  Space Telescope, obtained at the Space Telescope Science Institute,
  which is operated by the Association of Universities for Research in
  Astronomy, Inc. under NASA contract NAS5-26555, and the NASA-CNES-CSA
  Far Ultraviolet Explorer, which is operated for NASA by the Johns
  Hopkins University under NASA contract NAS5-32985.

Title: From Complete Linearization to ALI and Beyond
Authors: Hubeny, Ivan
Bibcode: 2009AIPC.1171....3H
Altcode:
  Starting with the ground-breaking work of Dimitri Mihalas and Larry
  Auer in the late 1960's and early 1970's, the progress in our ability
  to model and understand stellar atmospheres has been enormous. Here
  I briefly describe some efficient algorithms that were developed and
  applied to numerical simulations. An emphasis is given to efficient
  variants of the original Complete Linearization scheme, and to the
  methods that use the Accelerated Lambda Iteration and related methods.

Title: RECENT DIRECTIONS IN ASTROPHYSICAL QUANTITATIVE SPECTROSCOPY
AND RADIATION HYDRODYNAMICS: Proceedings of the International
    Conference in Honor of Dimitri Mihalas for His Lifetime Scientific
    Contributions on the Occasion of His 70th Birthday
Authors: Hubeny, Ivan; Stone, James M.; MacGregor, Keith; Werner, Klaus
Bibcode: 2009AIPC.1171.....H
Altcode:
  No abstract at ADS

Title: Quantitative Analysis of the Spectra of Early B Stars with
    Ultrasharp Lines
Authors: Peters, Geraldine J.; Adelman, Saul J.; Hubeny, Ivan;
   Lanz, Thierry
Bibcode: 2009AIPC.1171..345P
Altcode:
  We present selected results from an investigation that is currently
  underway to determine the abundances of light and Fe group elements
  in early B stars and assess the extent to which contemporary NLTE and
  LTE models represent their atmospheres. Spectral data of B stars that
  display ultrasharp lines, obtained with HST, FUSE, and the KPNO Coudé
  Feed Telescope, are compared with computations from TLUSTY/SYNSPEC
  and SYNTHE. The B stars include the abundance standards ι Her (B3V),
  HR 1886 (B1V), and HR 1887 (B0.5V).

Title: Beyond the classical paradigm of stellar winds: Investigating
    clumping, rotation and the weak wind problem in SMC O stars
Authors: Hubeny, Ivan
Bibcode: 2009hst..prop11625H
Altcode:
  SMC O stars provide an unrivaled opportunity to probe star formation,
  evolution, and the feedback of massive stars in an environment similar
  to the epoch of the peak in star formation history. Two recent
  breakthroughs in the study of hot, massive stars have important
  consequences for understanding the chemical enrichment and buildup
  of stellar mass in the Universe. The first is the realization that
  rotation plays a major role in influencing the evolution of massive
  stars and their feedback on the surrounding environment. The second
  is a drastic downward revision of the mass loss rates of massive stars
  coming from an improved description of their winds. STIS spectroscopy
  of SMC O stars combined with state-of-the-art NLTE analyses has
  shed new light on these two topics. A majority of SMC O stars reveal
  CNO-cycle processed material brought at their surface by rotational
  mixing. Secondly, the FUV wind lines of early O stars provide strong
  indications of the clumped nature of their wind. Moreover, we first
  drew attention to some late-O dwarfs showing extremely weak wind
  signatures. Consequently, we have derived mass loss rates from STIS
  spectroscopy that are significantly lower than the current theoretical
  predictions used in evolutionary models. Because of the limited size of
  the current sample {and some clear bias toward stars with sharp-lined
  spectra}, these results must however be viewed as tentative. Thanks to
  the high efficiency of COS in the FUV range, we propose now to obtain
  high-resolution FUV spectra with COS of a larger sample of SMC O stars
  to study systematically rotation and wind properties of massive stars
  at low metallicity. The analysis of the FUV wind lines will be based
  on our 2D extension of CMFGEN to model axi-symmetric rotating winds.

Title: A new detailed examination of white dwarfs in NGC 3532 and
    NGC 2287
Authors: Dobbie, P. D.; Napiwotzki, R.; Burleigh, M. R.; Williams,
   K. A.; Sharp, R.; Barstow, M. A.; Casewell, S. L.; Hubeny, I.
Bibcode: 2009MNRAS.395.2248D
Altcode: 2009arXiv0902.4259D; 2009MNRAS.tmp..480D
  We present the results of a photometric and spectroscopic study of the
  white dwarf candidate members of the intermediate age open clusters NGC
  3532 and NGC 2287. Of the nine objects investigated, it is determined
  that six are probable members of the clusters, four in NGC 3532 and
  two in NGC 2287. For these six white dwarfs, we use our estimates of
  their cooling times together with the cluster ages to constrain the
  lifetimes and masses of their progenitor stars. We examine the location
  of these objects in initial mass-final mass space and find that they
  now provide no evidence for substantial scatter in initial mass-final
  mass relation (IFMR) as suggested by previous investigations. Instead,
  we demonstrate that, when combined with current data from other solar
  metallicity open clusters and the Sirius binary system, they hint at
  an IFMR that is steeper in the initial mass range 3 M<SUB>solar</SUB>
  &lt;~ M<SUB>init</SUB> &lt;~ 4 M<SUB>solar</SUB> than at progenitor
  masses immediately lower and higher than this. This form is generally
  consistent with the predictions of stellar evolutionary models and can
  aid population synthesis models in reproducing the relatively sharp drop
  observed at the high mass end of the main peak in the mass distribution
  of white dwarfs. * <P />Based on observations made with ESO telescopes
  at the La Silla Paranal Observatory under programme IDs 079.D-0490(A)
  and 080.D-0654(A). <P />E-mail: pdd@aao.gov.au

Title: New faint optical spectrophotometric standards: hot white
    dwarfs from the Sloan Digital Sky Survey
Authors: Allende Prieto, Carlos; Hubeny, Ivan; Smith, J. Allyn
Bibcode: 2009MNRAS.396..759A
Altcode: 2009arXiv0903.2420A; 2009MNRAS.tmp..646A
  The spectral energy distributions for pure-hydrogen (DA) hot white
  dwarfs can be accurately predicted by model atmospheres. This makes
  it possible to define spectrophotometric calibrators by scaling the
  theoretical spectral shapes with broad-band photometric observations -
  a strategy successfully exploited for the spectrographs onboard the
  Hubble Space Telescope (HST) using three primary DA standards. Absolute
  fluxes for non-DA secondary standards, introduced to increase the
  density of calibrators in the sky, need to be referred to the primary
  standards, but a far better solution would be to employ a network
  of DA stars scattered throughout the sky. We search for blue objects
  in the sixth data release of the Sloan Digital Sky Survey (SDSS) and
  fit DA model fluxes to identify suitable candidates. Reddening needs
  to be considered in the analysis of many of these stars. We propose
  a list of nine pure-hydrogen white dwarfs with absolute fluxes with
  estimated uncertainties below 3 per cent, including four objects with
  estimated errors &lt;2 per cent, as candidates for spectrophotometric
  standards in the range 14 &lt; g &lt; 18, and provide model-based
  fluxes scaled to match the SDSS broad-band fluxes for each. We apply
  the same method to the three HST DA standards, linking the zero point
  of their absolute fluxes to ugr magnitudes transformed from photometry
  obtained with the US Naval Observatory 1-m telescope. For these stars,
  we estimate uncertainties of &lt;1 per cent in the optical, finding
  good consistency with the fluxes adopted for HST calibration.

Title: Effective area calibration of the reflection grating
    spectrometers of XMM-Newton. II. X-ray spectroscopy of DA white dwarfs
Authors: Kaastra, J. S.; Lanz, T.; Hubeny, I.; Paerels, F. B. S.
Bibcode: 2009A&A...497..311K
Altcode: 2009arXiv0902.2282K
  Context: White dwarf spectra have been widely used as a calibration
  source for X-ray and EUV instruments. The in-flight effective area
  calibration of the reflection grating spectrometers (RGS) of XMM-Newton
  depend upon the availability of reliable calibration sources. <BR
  />Aims: We investigate how well these white dwarf spectra can be used
  as standard candles at the lowest X-ray energies in order to gauge the
  absolute effective area scale of X-ray instruments. <BR />Methods:
  We calculate a grid of model atmospheres for Sirius B and HZ 43A,
  and adjust the parameters using several constraints until the ratio of
  the spectra of both stars agrees with the ratio as observed by the low
  energy transmission grating spectrometer (LETGS) of Chandra. This ratio
  is independent of any errors in the effective area of the LETGS. <BR
  />Results: We find that we can constrain the absolute X-ray spectrum
  of both stars with better than 5% accuracy. The best-fit model for
  both stars is close to a pure hydrogen atmosphere, and we put tight
  limits to the amount of helium or the thickness of a hydrogen layer
  in both stars. Our upper limit to the helium abundance in Sirius B
  is 4 times below the previous detection based on EUVE data. We also
  find that our results are sensitive to the adopted cut-off in the Lyman
  pseudo-continuum opacity in Sirius B. We get best agreement with a long
  wavelength cut-off. <BR />Conclusions: White dwarf model atmospheres
  can be used to derive the effective area of X-ray spectrometers in the
  lowest energy band. An accuracy of 3-4% in the absolute effective area
  can be achieved.

Title: Recent Progress in Modeling Stellar Atmospheres
Authors: Hubeny, I.; Lanz, T.
Bibcode: 2009ASSP....7..211H
Altcode: 2009nqsa.conf..211H
  We briefly review recent progress in modeling stellar atmospheres. We
  first summarize various levels of approximations being used in
  constructing the models, and present a brief overview of existing
  model atmosphere codes. We then concentrate on a description of our
  universal computer program Tlusty, and our recent grids of NLTE metal
  line blanketed model photospheres of O-stars - OSTAR2002 - and early
  B-stars - BSTAR2006.

Title: Spectrum and atmosphere models of irradiated transiting
    giant planets
Authors: Hubeny, Ivan; Burrows, Adam
Bibcode: 2009IAUS..253..239H
Altcode: 2008arXiv0807.3588H
  We show that a consistent fit to observed secondary eclipse data for
  several strongly irradiated transiting planets demands a temperature
  inversion (stratosphere) at altitude. Such a thermal inversion
  significantly influences the planet/star contrast ratios at the
  secondary eclipse, their wavelength dependences, and, importantly,
  the day-night flux contrast during a planetary orbit. The presence of
  the thermal inversion/stratosphere seems to roughly correlate with the
  stellar flux at the planet. Such temperature inversions might be caused
  by an upper-atmosphere absorber whose exact nature is still uncertain.

Title: Commission 29: Stellar Spectra
Authors: Parthasarathy, Mudumba; Piskunov, Nikolai E.; Sneden,
   Christopher; Carpenter, Kenneth G.; Castelli, Fiorella; Cunha, Katia;
   Eenens, Phillippe R. J.; Hubeny, Ivan; Rossi, Silvia; Takada-Hidai,
   Masahide; Wahlgren, Glenn M.; Weiss, Werner W.
Bibcode: 2009IAUTA..27..209P
Altcode:
  The members of IAU Commission 29 Stellar Spectra are actively
  engaged in the quantitative analysis of spectra of various types
  of stars. With large and medium size telescopes equipped with high
  resolution spectrographs LTE and Non-LTE analysis of spectra of all
  types stars are being carried out. Spectra of stars in our Galaxy,
  in globular and open clusters, stars in LMC and SMC and in nearby
  galaxies are being studied. Accurate chemical composition analysis
  of various types of stars has been carried out during the past three
  years. Now the analysis of stellar spectra covers the wavelength range
  from X-ray region to IR and sub-millimeter range. Recently stellar
  spectra are being analysed using time-dependent, 3D, hydrodynamical
  model atmospheres to derive accurate stellar abundances.

Title: NLTE model calculations for the solar atmosphere with an
    iterative treatment of opacity distribution functions
Authors: Haberreiter, M.; Schmutz, W.; Hubeny, I.
Bibcode: 2008A&A...492..833H
Altcode: 2008arXiv0810.3471H
  Context: Modeling the variability of the solar spectral irradiance is
  a key factor in understanding the Sun's influence on the climate of
  the Earth. <BR />Aims: As a first step toward calculating the solar
  spectral irradiance variations, we reproduce the solar spectrum
  for the quiet Sun over a broad wavelength range with an emphasis
  on the UV. <BR />Methods: We introduce the radiative transfer code
  COSI, which calculates solar synthetic spectra under conditions
  of non-local thermodynamic equilibrium (NLTE). A self-consistent
  simultaneous solution of the radiative transfer and the statistical
  equation for the level populations guarantees that the correct physics
  is considered for wavelength regions where the assumption of local
  thermodynamic equilibrium (LTE) breaks down. The new concept of
  iterated opacity distribution functions (NLTE-ODFs) is presented,
  through which all line opacities are included in the NLTE radiative
  transfer calculation. <BR />Results: We show that it is essential to
  include the line opacities in the radiative transfer to reproduce the
  solar spectrum in the UV. <BR />Conclusions: Through the implemented
  scheme of NLTE-ODFs, the COSI code is successful in reproducing the
  spectral energy distribution of the quiet Sun. <P />Table 2 is only
  available in electronic form at http://www.aanda.org

Title: Modeling UX Ursae Majoris: An Abundance of Challenges
Authors: Linnell, Albert P.; Godon, Patrick; Hubeny, Ivan; Sion,
   Edward M.; Szkody, Paula
Bibcode: 2008ApJ...688..568L
Altcode: 2008arXiv0807.3920L
  We present a system model for optical and far-UV spectra of the
  nova-like variable UX UMa involving a white dwarf, secondary star, gas
  stream, hot spot, and accretion disk using our code BINSYN and based
  on an initially adopted system distance. Calculated SED intensity
  data successfully fit successive tomographically extracted annuli
  longward of the Balmer limit but require a postulated "iron curtain"
  shortward of the Balmer limit that is applied to the annulus section
  closest to the secondary star, while postulated recombination emission
  fills in the model SED shortward of the Balmer limit and is applied
  to the annulus section more remote from the secondary star. The same
  model fits UBV 1954 light curves by Walker and Herbig. Fits to HST FOS
  spectra are approximate but require assumed time-variable changes in the
  SED. Comparable effects, possibly involving variable absorption, afflict
  FUSE spectra. Fits to IUE spectra by the model show time-dependent
  residuals that indicate changes in the accretion disk temperature
  profile, possibly indicative of a slightly variable \dot{M} from the
  secondary star. Using model-based component light contributions and the
  improvement on the Bailey relation by Knigge we determine the system
  distance and mass transfer rate. <P />Based on observations made with
  the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope
  Science Institute, which is operated by the Association of Universities
  for Research in Astronomy, Inc., under NASA contract NAS5-26555, and
  the NASA-CNES-CSA Far Ultraviolet Explorer, which is operated for NASA
  by the Johns Hopkins University under NASA contract NAS5-32985.

Title: Optical Albedo Theory of Strongly Irradiated Giant Planets:
    The Case of HD 209458b
Authors: Burrows, A.; Ibgui, L.; Hubeny, I.
Bibcode: 2008ApJ...682.1277B
Altcode: 2008arXiv0803.2523B
  We calculate a new suite of albedo models for close-in extrasolar
  giant planets and compare with the recent stringent upper limit
  for HD 209458b of Rowe et al. using MOST. We find that all models
  without scattering clouds are consistent with this optical limit. We
  explore the dependence on wavelength and wave band, metallicity, the
  degree of heat redistribution, and the possible presence of thermal
  inversions and find a rich diversity of behaviors. Measurements of
  transiting extrasolar giant planets (EGPs) at short wavelengths by
  MOST, Kepler, and CoRoT, as well as by proposed dedicated multiband
  missions, can complement measurements in the near- and mid-IR using
  Spitzer and JWST. Collectively, such measurements can help determine
  metallicity, compositions, atmospheric temperatures, and the cause
  of thermal inversions (when they arise) for EGPs with a broad range
  of radii, masses, degrees of stellar insolation, and ages. With this
  paper we reappraise and highlight the diagnostic potential of albedo
  measurements of hot EGPs shortward of ~1.3 μm.

Title: Hubble Space Telescope STIS Spectroscopy of Long-Period Dwarf
    Novae in Quiescence
Authors: Sion, Edward M.; Gänsicke, Boris T.; Long, Knox S.; Szkody,
   Paula; Knigge, Christian; Hubeny, Ivan; deMartino, Domitilla; Godon,
   Patrick
Bibcode: 2008ApJ...681..543S
Altcode: 2008arXiv0801.4703S
  We present the results of a synthetic spectral analysis of HST STIS
  spectra of five long-period dwarf novae obtained during their quiescence
  to determine the properties of their white dwarfs, which are little
  known for systems above the CV period gap. The five systems, TU Men,
  BD Pav, SS Aur, TT Crt, and V442 Cen, were observed as part of an HST
  Snapshot project. The spectra are described and fitted with combinations
  of white dwarf photospheres and accretion disks. We provide evidence
  that the white dwarfs in all five systems are at least partially
  exposed. We discuss the evolutionary implications of our model-fitting
  results and compare these dwarf novae to previously analyzed FUV
  spectra of other dwarf novae above the period gap. The dispersion
  in CV WD temperatures above the period gap is substantially greater
  than one finds below the period gap, where there is a surprisingly
  narrow dispersion in temperatures around 15,000 K. There appears to
  be a larger spread of surface temperatures in dwarf novae above the
  period than is seen below the gap.

Title: A Far Ultraviolet Archival Study of Cataclysmic
    Variables. I. FUSE and HST STIS Spectra of the Exposed White Dwarf
    in Dwarf Nova Systems
Authors: Godon, Patrick; Sion, Edward M.; Barrett, Paul E.; Hubeny,
   Ivan; Linnell, Albert P.; Szkody, Paula
Bibcode: 2008ApJ...679.1447G
Altcode: 2008arXiv0802.2022G
  We present a synthetic spectral analysis of Far Ultraviolet
  Spectroscopic Explorer (FUSE) and Hubble Space Telescope Space
  Telescope Imaging Spectrograph (HST STIS) spectra of five dwarf
  novae above and below the period gap during quiescence. We use our
  synthetic spectral code, including options for the treatment of the
  hydrogen quasi-molecular satellite lines (for low-temperature stellar
  atmospheres), non-LTE (NLTE) approximation (for high-temperature stellar
  atmospheres), and for one system (RU Peg) we model the interstellar
  medium (ISM) molecular and atomic hydrogen lines. In all the systems
  presented here the FUV flux continuum is due to the white dwarf
  (WD). These spectra also exhibit some broad emission lines. In this
  work we confirm some of the previous FUV analysis results, but we also
  present new results. For four systems we combine the FUSE and STIS
  spectra to cover a larger wavelength range and to improve the spectral
  fit. This work is part of our broader HST archival research program,
  in which we aim to provide accurate system parameters for cataclysmic
  variables above and below the period gap by combining FUSE and HST
  FUV spectra. <P />Based on observations made with the NASA-CNES-CSA
  Far Ultraviolet Spectroscopic Explorer. FUSE is operated for NASA by
  the Johns Hopkins University under NASA contract NAS5-32985.

Title: Argon Abundances in the Solar Neighborhood: Non-LTE Analysis
    of Orion Association B-Type Stars
Authors: Lanz, Thierry; Cunha, Katia; Holtzman, Jon; Hubeny, Ivan
Bibcode: 2008ApJ...678.1342L
Altcode: 2007arXiv0709.2147L
  Argon abundances have been derived for a sample of B main-sequence
  stars in the Orion association. The abundance calculations are based on
  non-LTE (NLTE) metal line-blanketed model atmospheres calculated with
  the NLTE code TLUSTY and an updated and complete argon model atom. We
  derive an average argon abundance for this young population of A(Ar)
  = 6.66 +/- 0.06. While our result is in excellent agreement with a
  recent analysis of the Orion Nebula, it is significantly higher than
  the currently recommended solar value, which is based on abundance
  measurements in the solar corona. Moreover, the derived argon abundances
  in the Orion B stars agree very well with a measurement from a solar
  impulsive flare during which unmodified solar photospheric material
  was brought to flare conditions. We therefore argue that the argon
  abundances obtained independently for both the Orion B stars and the
  Orion Nebula are representative of the disk abundance value in the
  solar neighborhood. The lower coronal abundance may reflect a depletion
  related to the first ionization potential (FIP) effect. We propose a new
  reference value for the abundance of argon in the solar neighborhood,
  A(Ar) = 6.63 +/- 0.10, corresponding to Ar/O = 0.009 +/- 0.002. <P
  />Based on observations obtained with the Apache Point Observatory
  3.5 m telescope, which is owned and operated by the Astrophysical
  Research Consortium.

Title: Theoretical Spectra and Light Curves of Close-in Extrasolar
    Giant Planets and Comparison with Data
Authors: Burrows, A.; Budaj, J.; Hubeny, I.
Bibcode: 2008ApJ...678.1436B
Altcode: 2007arXiv0709.4080B
  We present theoretical atmosphere, spectral, and light-curve models for
  extrasolar giant planets (EGPs) undergoing strong irradiation for which
  Spitzer planet/star contrast ratios or light curves have been published
  (circa 2007 June). These include HD 209458b, HD 189733b, TrES-1, HD
  149026b, HD 179949b, and υ And b. By comparing models with data, we
  find that a number of EGP atmospheres experience thermal inversions
  and have stratospheres. This is particularly true for HD 209458b,
  HD 149026b, and υ And b. This finding translates into qualitative
  changes in the planet/star contrast ratios at secondary eclipse and in
  close-in EGP orbital light curves. Moreover, the presence of atmospheric
  water in abundance is fully consistent with all the Spitzer data for
  the measured planets. For planets with stratospheres, water absorption
  features invert into emission features and mid-infrared fluxes can be
  enhanced by a factor of 2. In addition, the character of near-infrared
  planetary spectra can be radically altered. We derive a correlation
  between the importance of such stratospheres and the stellar flux on
  the planet, suggesting that close-in EGPs bifurcate into two groups:
  those with and without stratospheres. From the finding that TrES-1
  shows no signs of a stratosphere, while HD 209458b does, we estimate
  the magnitude of this stellar flux breakpoint. We find that the heat
  redistribution parameter, P<SUB>n</SUB>, for the family of close-in
  EGPs assumes values from ~0.1 to ~0.4. This paper provides a broad
  theoretical context for the future direct characterization of EGPs in
  tight orbits around their illuminating stars.

Title: Synthetic Spectrum Constraints on a Model of the Cataclysmic
    Variable QU Carinae
Authors: Linnell, Albert P.; Godon, Patrick; Hubeny, Ivan; Sion,
   Edward M.; Szkody, Paula; Barrett, Paul E.
Bibcode: 2008ApJ...676.1226L
Altcode: 2008arXiv0801.0704L
  Neither standard model SEDs nor truncated standard model SEDs fit
  observed spectra of QU Carinae with acceptable accuracy over the
  range 900-3000 Å. Nonstandard model SEDs fit the observation set
  accurately. The nonstandard accretion disk models have a hot region
  extending from the white dwarf to R = 1.36R<SUB>WD</SUB>, a narrow
  intermediate-temperature annulus, and an isothermal remainder to
  the tidal cutoff boundary. The models include a range of \dot{M}
  values between 1.0 × 10<SUP>-7</SUP> and 1.0 × 10<SUP>-6</SUP>
  M<SUB>⊙</SUB> yr<SUP>-1</SUP> and limiting values of M<SUB>WD</SUB>
  between 0.6 and 1.2 M<SUB>⊙</SUB>. A solution with M<SUB>WD</SUB>
  = 1.2 M<SUB>⊙</SUB> is consistent with an empirical mass-period
  relation. The set of models agree on a limited range of possible
  isothermal region T<SUB>eff</SUB> values between 14,000 and 18,000
  K. The model-to-model residuals are so similar that it is not
  possible to choose a best model. The Hipparcos distance, 610 pc, is
  representative of the model results. The orbital inclination is between
  40° and 60°. <P />Based on observations made with the NASA/ESA Hubble
  Space Telescope, obtained at the Space Telescope Science Institute,
  which is operated by the Association of Universities for Research in
  Astronomy, Inc., under NASA contract NAS5-26555, and the NASA-CNES-CSA
  Far Ultraviolet Explorer, which is operated for NASA by the Johns
  Hopkins University under NASA contract NAS5-32985.

Title: White Dwarf Spectra and Calibration of X-ray Grating
    Spectrometers
Authors: Kaastra, Jelle S.; Lanz, T.; Hubeny, I.; Paerels, F.
Bibcode: 2008HEAD...10.0406K
Altcode:
  White dwarf spectra have been widely used as calibration sources for
  X-ray and EUV instruments. The in-flight effective area calibration
  of the RGS of XMM-Newton and of the LETGS of Chandra depend upon the
  availability of reliable calibration sources. We calculate a grid of
  model atmospheres for Sirius B and HZ 43A, and adjust the parameters
  using several constraints until the ratio of the spectra of both stars
  agrees with the ratio observed with the LETGS of Chandra. This ratio
  is independent of any errors in the effective area of the LETGS. We
  determine how accurately the effective area of the LETGS is determined
  using our method, and find interesting constraints on the parameters
  for both stars. We discuss the role of the Lyman pseudo-continuum
  in the calculation of the spectrum of Sirius B. The treatment of
  that pseudo-continuum appears to play a fundamental role in the
  ultimate accuracy that can be reached. With the proper treatment of
  the pseudo-continuum, the soft X-ray flux of both stars and thereby
  the absolute effective area of the LETGS can be determined with an
  uncertainty of less than 5 %.

Title: A Systematic Study of Departures from Chemical Equilibrium
    in the Atmospheres of Substellar Mass Objects
Authors: Hubeny, Ivan; Burrows, Adam
Bibcode: 2007ApJ...669.1248H
Altcode: 2007arXiv0705.3922H
  We present a systematic study of the spectral consequences of departures
  from chemical equilibrium in the atmospheres of L and T dwarfs,
  and for even cooler dwarfs. The temperature/pressure profiles of the
  nonequilibrium models are fully consistent with the nonequilibrium
  chemistry. Our grid of nonequilibrium models includes spectra for
  effective temperatures from 200 to 1800 K, three surface gravities,
  four possible values of the coefficient of eddy diffusion in the
  radiative zone, and three different CO/CH<SUB> 4</SUB> chemical reaction
  prescriptions. We also provide clear and cloudy model variants. We find,
  in keeping with previous studies, that there are essentially only
  two spectral regions where the effects of departures from chemical
  equilibrium can influence the predicted spectrum. These are in the
  M (~4-5 μm) and N (8-14 μm) bands due to CO and NH<SUB> 3</SUB>,
  respectively. The overabundance of CO translates into flux suppressions
  of at most ~40% between effective temperatures of 600 and 1800 K. The
  effect is largest around T<SUB>eff</SUB>~1100 K. The underabundance
  of ammonia translates into flux enhancements of no more than ~20%
  for the T<SUB>eff</SUB> range from 300 to 1800 K, with the largest
  effects at the lowest values of T<SUB>eff</SUB>. The magnitude of the
  departure from chemical equilibrium increases with decreasing gravity,
  with increasing eddy diffusion coefficient, and with decreasing speed
  of the CO/CH<SUB>4</SUB> reaction. Although these effects are modest,
  they lead to better fits with the measured T dwarf spectra. Furthermore,
  the suppression in the M band due to nonequilibrium enhancements in the
  CO abundance disappears below ~500 K, and is only partial above ~500 K,
  preserving the M-band flux as a useful diagnostic of cool atmospheres
  and maintaining its importance for searches for the cooler brown dwarfs
  beyond the T dwarfs.

Title: A Statistical Study of Accretion Disk Model Spectra for
    Cataclysmic Variables
Authors: Puebla, Raúl E.; Diaz, Marcos P.; Hubeny, Ivan
Bibcode: 2007AJ....134.1923P
Altcode:
  We have performed a statistical test of the currently used accretion
  disk models for cataclysmic variables (CVs) using a set of 33 CVs
  with steady disks (10 old novae and 23 nova-like systems). The mass
  transfer rate () for each system was also calculated. Ultraviolet (UV)
  data were fitted by model spectra using a multiparametric optimization
  method, aiming to constrain the values. It was verified that these
  accretion disk models fail to fit both color and flux simultaneously,
  as previously noted when composite stellar atmosphere models were
  fitted to the UV spectra of CVs by Wade. By applying such models to a
  sample of novae and nova-like CVs, we confirm that the limb-darkening
  effect must be taken into account when estimating mass transfer rates,
  especially for high-inclination systems. Important fitting degeneracies
  of the basic disk parameters are analyzed. Our simulations suggest that
  to reproduce the observations a revision of the temperature profile,
  at least in the innermost parts of the disk, seems to be required,
  and possibly the vertical distribution of the viscosity should be
  revised. In addition, an optically thin layer or an extended disk
  component should be considered. This component may be physically
  represented by a disk wind and/or a chromosphere. A physical description
  of the emission-line profiles may help to break the degeneracies that
  appear when only the continuum is analyzed. The average value of found
  for nova-like systems is ~9.3 × 10<SUP>-9</SUP> M<SUB>odot</SUB>
  yr<SUP>-1</SUP>, while ~1.3 × 10<SUP>-8</SUP> M<SUB>odot</SUB>
  yr<SUP>-1</SUP> is found for old classical novae. No clear evidence
  is found for either the presence or absence of a correlation between
  and the orbital period. Such correlation analysis was performed for
  high accretion rate systems (15 nova-like systems and 10 old novae),
  but we were not able to find a well-defined correlation as found by
  Patterson. By measuring the equivalent width of the emission lines
  (C IV λ1550 and He II λ1640) we found a lack of systems with low and
  strong UV emission lines. A correlation between the equivalent width
  of such lines and the orbital inclination (i) was also confirmed.

Title: Theoretical Spectral Models of the Planet HD 209458b with a
    Thermal Inversion and Water Emission Bands
Authors: Burrows, A.; Hubeny, I.; Budaj, J.; Knutson, H. A.;
   Charbonneau, D.
Bibcode: 2007ApJ...668L.171B
Altcode: 2007arXiv0709.3980B
  We find that a theoretical fit to all the HD 209458b data at secondary
  eclipse requires that the day-side atmosphere of HD 209458b have
  a thermal inversion and a stratosphere. This inversion is caused
  by the capture of optical stellar flux by an absorber of uncertain
  origin that resides at altitude. One consequence of stratospheric
  heating and temperature inversion is the flipping of water absorption
  features into emission features from the near- to the mid-infrared,
  and we see evidence of such a water emission feature in the recent HD
  209458b IRAC data of Knutson et al. In addition, an upper-atmosphere
  optical absorber may help explain both the weaker-than-expected Na
  D feature seen in transit and the fact that the transit radius at 24
  μm is smaller than the corresponding radius in the optical. Moreover,
  it may be a factor in why HD 209458b's optical transit radius is as
  large as it is. We speculate on the nature of this absorber and the
  planets whose atmospheres may, or may not, be affected by its presence.

Title: Comparative study of dust cloud modelling for substellar
    atmospheres
Authors: Helling, Ch.; Ackerman, A. S.; Allard, F.; Dehen, M.;
   Hauschildt, P.; Hubeny, I.; Homeier, D.; Lodders, K.; Marley, M.;
   Tsuji, T.; Woitke, P.
Bibcode: 2007AN....328..655H
Altcode:
  No abstract at ADS

Title: Professor Mirek J. Plavec
Authors: Harmanec, Petr; Grygar, Jiří; Batten, Alan H.; Peters,
   Geraldine J.; Linnell, Albert P.; Hubeny, Ivan; Guinan, Edward F.
Bibcode: 2007IAUS..240...17H
Altcode:
  No abstract at ADS

Title: A Synthetic Spectrum and Light-Curve Analysis of the
    Cataclysmic Variable IX Velorum
Authors: Linnell, Albert P.; Godon, Patrick; Hubeny, Ivan; Sion,
   Edward M.; Szkody, Paula
Bibcode: 2007ApJ...662.1204L
Altcode: 2006astro.ph.12657L
  Spectrum synthesis analysis of FUSE and STIS spectra for the cataclysmic
  variable IX Vel shows that it is possible to achieve a close synthetic
  spectrum fit with a mass transfer rate of M˙=5×10<SUP>-9</SUP>
  M<SUB>solar</SUB> yr<SUP>-1</SUP> and a modified standard model
  temperature profile. The innermost four annuli of the accretion disk
  model, extending to r/r<SUB>WD</SUB>~4, are isothermal; beyond that
  limit the temperatures follow the standard model. A light synthesis
  fit to K-band photometry requires shallow eclipses of the accretion
  disk rim and secondary star limb. The geometry constrains the orbital
  inclination to i=57<SUP>deg</SUP>+/-2<SUP>deg</SUP>. The synthetic
  light curve requires a vertically extended accretion disk rim, beyond
  that predicted by gravitational equilibrium, to shadow the secondary
  star. The enhanced vertical extension is consistent with recent MHD
  predictions for CV accretion disks. Matching differing observed heights
  of alternate K-band light-curve maxima requires a warm rim region
  downstream of the intersection point of the mass transfer stream
  with the accretion disk rim. The temperature of the warm region is
  inconsistent with expectation for a bright spot associated with a
  rim shock. <P />Based on observations made with the NASA/ESA Hubble
  Space Telescope, obtained at the Space Telescope Science Institute,
  which is operated by the Association of Universities for Research in
  Astronomy, Inc., under NASA contract NAS5-26555, and the NASA-CNES-CSA
  Far Ultraviolet Spectroscopic Explorer, which is operated for NASA by
  Johns Hopkins University under NASA contract NAS5-32985.

Title: VizieR Online Data Catalog: VLT-FLAMES survey of massive stars
    (Hunter+, 2007)
Authors: Hunter, I.; Dufton, P. L.; Smartt, S. J.; Ryans, R. S. I.;
   Evans, C. J.; Lennon, D. J.; Trundle, C.; Hubeny, I.; Lanz, T.
Bibcode: 2007yCat..34660277H
Altcode:
  Files table3.dat, table4.dat and table5.dat contain the equivalent
  widths and abundances estimates of the observed metal lines for
  B-type stars in NGC 6611, N11 and NGC 346 respectively. The equivalent
  widths of the spectral lines have been measured using the line fitting
  program ELF in the spectral analysis package DIPSO (Howarth et al.,
  1994, Starlink User Note, No. 50.15). The nitrogen equivalent widths
  and abundances are upper limits for objects N11-037, N11-047, N11-101,
  NGC 346-029, NGC 346-039, NGC 346-040, NGC 346-043, NGC 346-044 and
  NGC 346-075. <P />table6.dat contains details of the adopted atomic
  data for the absorption lines considered in this analysis. Model atoms
  are discussed in Lanz &amp; Hubeny (2003ApJS..146..417L) and Allende
  Prieto et al. (2003ApJS..147..363A), see Dufton et al. (2005, Cat. )
  for further details. Note, the loggf values of the Si II lines at 4128
  and 4131 angstroms have been updated to include improved atomic data
  (A. Korn, private communication). <P />(5 data files).

Title: Possible Solutions to the Radius Anomalies of Transiting
    Giant Planets
Authors: Burrows, A.; Hubeny, I.; Budaj, J.; Hubbard, W. B.
Bibcode: 2007ApJ...661..502B
Altcode: 2006astro.ph.12703B
  We calculate the theoretical evolution of the radii of all 14 of
  the known transiting extrasolar giant planets (EGPs) for a variety of
  assumptions concerning atmospheric opacity, dense inner core masses, and
  possible internal power sources. We incorporate the effects of stellar
  irradiation and customize such effects for each EGP and star. Looking
  collectively at the family as a whole, we find that there are in
  fact two radius anomalies to be explained. Not only are the radii
  of a subset of the known transiting EGPs larger than expected from
  previous theory, but many of the other objects are smaller than the
  default theory would allow. We suggest that the larger EGPs can be
  explained by invoking enhanced atmospheric opacities that naturally
  retain internal heat. This explanation might obviate the necessity for
  an extra internal power source. We explain the smaller radii by the
  presence in perhaps all the known transiting EGPs of dense cores, such
  as have been inferred for Saturn and Jupiter. Importantly, we derive a
  rough correlation between the masses of our ``best-fit'' cores and the
  stellar metallicity that seems to buttress the core-accretion model
  of their formation. Although many caveats and uncertainties remain,
  the resulting comprehensive theory that incorporates enhanced-opacity
  atmospheres and dense cores is in reasonable accord with all the
  current structural data for the known transiting giant planets.

Title: Effects of mass loss for highly-irradiated giant planets
Authors: Hubbard, W. B.; Hattori, M. F.; Burrows, A.; Hubeny, I.;
   Sudarsky, D.
Bibcode: 2007Icar..187..358H
Altcode:
  We present calculations for the evolution and surviving mass of
  highly-irradiated extrasolar giant planets (EGPs) at orbital semimajor
  axes ranging from 0.023 to 0.057 AU using a generalized scaled theory
  for mass loss, together with new surface-condition grids for hot EGPs
  and a consistent treatment of tidal truncation. Theoretical estimates
  for the rate of energy-limited hydrogen escape from giant-planet
  atmospheres differ by two orders of magnitude, when one holds planetary
  mass, composition, and irradiation constant. Baraffe et al. [Baraffe,
  I., Selsis, F., Chabrier, G., Barman, T.S., Allard, F., Hauschildt,
  P.H., Lammer, H., 2004. Astron. Astrophys. 419, L13-L16] predict
  the highest rate, based on the theory of Lammer et al. [Lammer,
  H., Selsis, F., Ribas, I., Guinan, E.F., Bauer, S.J., Weiss, W.W.,
  2003. Astrophys. J. 598, L121-L124]. Scaling the theory of Watson et
  al. [Watson, A.J., Donahue, T.M., Walker, J.C.G., 1981. Icarus 48,
  150-166] to parameters for a highly-irradiated exoplanet, we find
  an escape rate ∼10 lower than Baraffe's. With the scaled Watson
  theory we find modest mass loss, occurring early in the history of a
  hot EGP. In this theory, mass loss including the effect of Roche-lobe
  overflow becomes significant primarily for masses below a Saturn mass,
  for semimajor axes ⩾0.023 AU. This contrasts with the Baraffe model,
  where hot EGPs are claimed to be remnants of much more massive bodies,
  originally several times Jupiter and still losing substantial mass
  fractions at present.

Title: The VLT-FLAMES survey of massive stars: surface chemical
    compositions of B-type stars in the Magellanic Clouds
Authors: Hunter, I.; Dufton, P. L.; Smartt, S. J.; Ryans, R. S. I.;
   Evans, C. J.; Lennon, D. J.; Trundle, C.; Hubeny, I.; Lanz, T.
Bibcode: 2007A&A...466..277H
Altcode: 2006astro.ph..9710H
  We present an analysis of high-resolution FLAMES spectra of
  approximately 50 early B-type stars in three young clusters at different
  metallicities, NGC 6611 in the Galaxy, N 11 in the Large Magellanic
  Cloud (LMC) and NGC 346 in the Small Magellanic Cloud (SMC). Using
  the tlusty non-LTE model atmospheres code, atmospheric parameters and
  photospheric abundances (C, N, O, Mg and Si) of each star have been
  determined. These results represent a significant improvement on the
  number of Magellanic Cloud B-type stars with detailed and homogeneous
  estimates of their atmospheric parameters and chemical compositions. The
  relationships between effective temperature and spectral type are
  discussed for all three metallicity regimes, with the effective
  temperature for a given spectral type increasing as one moves to a
  lower metallicity regime. Additionally the difficulties in estimating
  the microturbulent velocity and the anomalous values obtained,
  particularly in the lowest metallicity regime, are discussed. Our
  chemical composition estimates are compared with previous studies,
  both stellar and interstellar with, in general, encouraging agreement
  being found. Abundances in the Magellanic Clouds relative to the
  Galaxy are discussed and we also present our best estimates of the
  base-line chemical composition of the LMC and SMC as derived from B-type
  stars. Additionally we discuss the use of nitrogen as a probe of the
  evolutionary history of stars, investigating the roles of rotational
  mixing, mass-loss, blue loops and binarity on the observed nitrogen
  abundances and making comparisons with stellar evolutionary models
  where possible. <P />Based on observations at the European Southern
  Observatory in programmes 171.0237 and 073.0234. Tables 3-6 and
  Figs. 7-31 are only available in electronic form at http://www.aanda.org

Title: A New Algorithm for Two-Dimensional Transport for Astrophysical
    Simulations. I. General Formulation and Tests for the One-Dimensional
    Spherical Case
Authors: Hubeny, Ivan; Burrows, Adam
Bibcode: 2007ApJ...659.1458H
Altcode: 2006astro.ph..9049H
  We derive new equations using the mixed-frame approach for one- and
  two-dimensional (axisymmetric) time-dependent radiation transport and
  the associated couplings with matter. Our formulation is multigroup
  and multiangle and includes anisotropic scattering, frequency
  (energy)-dependent scattering and absorption, complete velocity
  dependence to order v/c, rotation, and energy redistribution due to
  inelastic scattering. Hence, the ``2D'' realization is actually ``6
  1/2''-dimensional. The effects of radiation viscosity are automatically
  incorporated. Moreover, we develop accelerated lambda iteration,
  Krylov subspace (GMRES), discontinuous finite element, and Feautrier
  numerical methods for solving the equations and present the results
  of one-dimensional numerical tests of the new formalism. The virtues
  of the mixed-frame approach include simple velocity dependence with
  no velocity derivatives, straight characteristics, simple physical
  interpretation, and clear generalization to higher dimensions. Our
  treatment can be used for both photon and neutrino transport, but we
  focus on neutrino transport and applications to core-collapse supernova
  theory in the discussions and examples.

Title: A Grid of NLTE Line-blanketed Model Atmospheres of Early
    B-Type Stars
Authors: Lanz, Thierry; Hubeny, Ivan
Bibcode: 2007ApJS..169...83L
Altcode: 2006astro.ph.11891L
  We have constructed a comprehensive grid of 1540 metal line-blanketed,
  NLTE, plane-parallel, hydrostatic model atmospheres for the basic
  parameters appropriate to early B-type stars. The BSTAR2006
  grid considers 16 values of effective temperatures, 15,000
  K&lt;=T<SUB>eff</SUB>&lt;=30,000 K with 1000 K steps, 13 surface
  gravities, 1.75&lt;=logg&lt;=4.75 with 0.25 dex steps, six chemical
  compositions, and a microturbulent velocity of 2 km s<SUP>-1</SUP>. The
  lower limit of logg for a given effective temperature is set by an
  approximate location of the Eddington limit. The selected chemical
  compositions range from twice to one-tenth of the solar metallicity
  and metal-free. Additional model atmospheres for B supergiants
  (logg&lt;=3.0) have been calculated with a higher microturbulent
  velocity (10 km s<SUP>-1</SUP>) and a surface composition that is
  enriched in helium and nitrogen and depleted in carbon. This new grid
  complements our earlier OSTAR2002 grid of O-type stars (our Paper
  I). The paper contains a description of the BSTAR2006 grid and some
  illustrative examples and comparisons. NLTE ionization fractions,
  bolometric corrections, radiative accelerations, and effective
  gravities are obtained over the parameter range covered by the grid. By
  extrapolating radiative accelerations, we have determined an improved
  estimate of the Eddington limit in absence of rotation between 55,000
  and 15,000 K. The complete BSTAR2006 grid is available at the TLUSTY
  Web site.

Title: Commission 29: Stellar Spectra
Authors: Sneden, Christopher; Parthasarathy, M.; Castelli, Fiorella;
   Cunha, Katia; Eenens, Philippe; Friel, Eileen; Gratton, Raffaele;
   Hubeny, Ivan; Landstreet, John D.; Mathys, Gautier; Piskunov, Nikolai;
   Primas, Francesca; Takada-Hidai, Masahide; Weiss, Werner
Bibcode: 2007IAUTA..26..203S
Altcode:
  Participants in Commission 29 study various aspects of stellar spectra
  and the information that can be extracted from spectra. The list
  of fields of interest of the Organizing Committee members suggest
  some major current research topics in this area are stellar chemical
  compositions and surface/envelope phenomena. Some of the topics of this
  commission have overlap with other commissions, such as Commission
  14 (Atomic and Molecular Data), 26 (Double and Multiple Stars),
  27 (Variable Stars), 30 (Radial Velocities), 36 (Theory of Stellar
  Atmospheres), and 37 (Star Clusters and Associations). Many Commission
  29 members are also members of these other commissions.

Title: A Mass Function Constraint on Extrasolar Giant Planet
    Evaporation Rates
Authors: Hubbard, W. B.; Hattori, M. F.; Burrows, A.; Hubeny, I.
Bibcode: 2007ApJ...658L..59H
Altcode: 2007astro.ph..2276H
  The observed mass function for all known extrasolar giant planets
  (EGPs) varies approximately as M<SUP>-1</SUP> for mass M between ~0.2
  Jupiter masses (M<SUB>J</SUB>) and ~5 M<SUB>J</SUB>. In order to study
  evaporation effects for highly irradiated EGPs in this mass range, we
  have constructed an observational mass function for a subset of EGPs in
  the same mass range but with orbital radii &lt;0.07 AU. Surprisingly,
  the mass function for such highly irradiated EGPs agrees quantitatively
  with the M<SUP>-1</SUP> law, implying that the mass function for EGPs
  is preserved despite migration to small orbital radii. Unless there
  is a remarkable compensation of mass-dependent orbital migration
  for mass-dependent evaporation, this result places a constraint on
  orbital migration models and rules out the most extreme mass-loss
  rates in the literature. A theory that predicts more moderate mass
  loss gives a mass function that is closer to observed statistics but
  still disagrees for M&lt;1 M<SUB>J</SUB>.

Title: An Illustration of Modeling Cataclysmic Variables: HST, FUSE,
    and SDSS Spectra of SDSS J080908.39+381406.2
Authors: Linnell, Albert P.; Hoard, D. W.; Szkody, Paula; Long,
   Knox S.; Hubeny, Ivan; Gänsicke, Boris; Sion, Edward M.
Bibcode: 2007ApJ...654.1036L
Altcode: 2006astro.ph.12692L
  FUSE, HST, and SDSS spectra of the cataclysmic variable SDSS
  J080908.39+381406.2 provide a spectral flux distribution from 900 to
  9200 Å. This data set is used to illustrate procedures for calculating
  and testing system models. The spectra are not contemporaneous; it
  is necessary to assume that the combined spectra are representative
  of the system. The illustrations are based on a system with a 1.0
  M<SUB>solar</SUB> white dwarf, a 0.30 M<SUB>solar</SUB>, 3500 K,
  Roche lobe-filling secondary star, and an accretion disk extending
  to the tidal cutoff radius. Assuming a similar accretion state for
  the nonsimultaneous spectra, the best standard model fit is with
  a mass transfer rate of 3.0 × 10<SUP>-9</SUP>M<SUB>solar</SUB>
  yr<SUP>-1</SUP>. Extensive simulations demonstrate that the accretion
  disk must be truncated at its inner edge if the temperature profile
  follows the standard model, but truncated models face severe
  objections, which we address. Following additional simulation
  tests, we obtain a model accretion disk with a temperature profile
  comparable to the profile for SW Sex as determined from tomographic
  image reconstruction. This model fits the discovery SDSS spectrum
  well but has a flux deficit in the UV and FUV. Emission from a white
  dwarf is a plausible source of additional flux. Adding this source
  to the disk synthetic spectrum produces FUV flux that can explain
  the observed flux. An additional (archival) SDSS spectrum is fainter
  by about 0.3 mag in the optical. Additional analysis showed that UV
  residuals from a model fitting the archival optical wavelength spectrum
  are unacceptably large. Contemporaneous spectra from all wavelength
  regions would be necessary for a reliable system model. Our discussion
  illustrates how this conclusion follows from the system models. <P
  />Based on observations made with the NASA/ESA Hubble Space Telescope,
  obtained at the Space Telescope Science Institute, which is operated by
  the Association of Universities for Research in Astronomy, Inc. under
  NASA contract NAS5-26555, the NASA-CNES-CSA Far Ultraviolet Explorer,
  which is operated for NASA by the Johns Hopkins University under
  NASA contract NAS5-32985, and with the Apache Point Observatory 3.5 m
  telescope, which is operated by the Astrophysical Research Corporation.

Title: Theory for the Secondary Eclipse Fluxes, Spectra, Atmospheres,
    and Light Curves of Transiting Extrasolar Giant Planets
Authors: Burrows, A.; Sudarsky, D.; Hubeny, I.
Bibcode: 2006ApJ...650.1140B
Altcode: 2006astro.ph..7014B
  We have created a general methodology for calculating the
  wavelength-dependent light curves of close-in extrasolar giant planets
  (EGPs) as they traverse their orbits. Focusing on the transiting EGPs
  HD 189733b, TrES-1, and HD 209458b, we calculate planet/star flux
  ratios during secondary eclipse and compare them with the Spitzer
  data points obtained so far in the mid-infrared. We introduce a
  simple parameterization for the redistribution of heat to the planet's
  night side, derive constraints on this parameter (P<SUB>n</SUB>), and
  provide a general set of predictions for planet/star contrast ratios
  as a function of wavelength, model, and phase. Moreover, we calculate
  average dayside and nightside atmospheric temperature/pressure profiles
  for each transiting planet/P<SUB>n</SUB> pair with which existing and
  anticipated Spitzer data can be used to probe the atmospheric thermal
  structure of severely irradiated EGPs. We find that the baseline models
  do a good job of fitting the current secondary eclipse data set, but
  that the Spitzer error bars are not yet small enough to discriminate
  cleanly among all the various possibilities.

Title: Neon Abundances in B Stars of the Orion Association: Solving
    the Solar Model Problem?
Authors: Cunha, Katia; Hubeny, Ivan; Lanz, Thierry
Bibcode: 2006ApJ...647L.143C
Altcode: 2006astro.ph..6738C
  We report on non-LTE Ne abundances for a sample of B-type stellar
  members of the Orion association. The abundances were derived by means
  of non-LTE fully metal-blanketed model atmospheres and extensive model
  atoms with updated atomic data. We find that these young stars have
  a very homogeneous abundance of A(Ne)=8.11+/-0.04. This abundance
  is higher by ~0.3 dex than the currently adopted solar value,
  A(Ne)=7.84, which is derived from lines produced in the corona and
  active regions. The general agreement between the abundances of C, N,
  and O derived for B stars with the solar abundances of these elements
  derived from three-dimensional hydrodynamical models atmospheres
  strongly suggests that the abundance patterns of the light elements in
  the Sun and B stars are broadly similar. If this hypothesis is true,
  then the Ne abundance derived here will help to reconcile solar models
  with helioseismological observations.

Title: VizieR Online Data Catalog: SMC NGC 346-11 and AV 304 spectra
    (Hunter+, 2005)
Authors: Hunter, I.; Dufton, P. L.; Ryans, R. S. I.; Lennon, D. J.;
   Rolleston, W. R. J.; Hubeny, I.; Lanz, T.
Bibcode: 2006yCat..34360687H
Altcode:
  High-resolution spectra have been obtained for both NGC 346-11 and AV
  304 using the Ultraviolet and Visual Echelle Spectrograph, UVES, on
  the UT2 (Kueyen) telescope at the European Southern Observatory. NGC
  346-11 was observed during a three night run in November 2001,
  whilst the observations of AV 304, taken during a two night run
  in January 2001, have been previously discussed by Rolleston et
  al. (2003A&amp;A...400...21R). <P />(1 data file).

Title: A FUSE Legacy Program of DA White Dwarf Observations
Authors: Holberg, J. B.; Sing, D. K.; Hubeny, I.; Barstow, M. A.;
   Burleigh, M. R.
Bibcode: 2006ASPC..348..230H
Altcode:
  We are currently conducting a Cycle 5 Legacy program designed to fill
  critical gaps in the FUSE coverage of hot DA white dwarf stars. In
  particular this program will systematically sample stars in the
  temperature region above 50,000 K as well as cover the widest possible
  range of surface gravities. The specific scientific objective of this
  program is to resolve the recently discovered discrepancy between
  Lyman line and Balmer line temperature determinations that is evident
  for DA white dwarfs above 50,000 K. This program is now underway,
  with three of our 24 targets having been observed.

Title: FUSE Spectroscopy of Hybrid White Dwarfs
Authors: Lanz, T.; Holberg, J. B.; Hubeny, I.
Bibcode: 2006ASPC..348..197L
Altcode:
  We have obtained FUSE spectra of three white dwarfs showing hybrid
  helium and hydrogen spectra. We present initial results of our
  NLTE model atmosphere analysis, and discuss their implication for
  understanding the origin of DAB white dwarfs and the physical processes
  in white dwarf atmospheres.

Title: The RXTE, ROSAT, IUE, EUVE, Optical Campaign Covering the
    45-Day Supercycle of V1159 Orionis
Authors: Szkody, P.; Honeycutt, K.; Robertson, J.; Silber, A.; Hoard,
   D. W.; Pastwick, L.; Hubeny, I.; Cannizzo, J.; Liller, W.; Zissell,
   R.; Walker, G.; La Dous, C.; Drew, J.
Bibcode: 2006JAVSO..35..135S
Altcode:
  A comprehensive data set covering the superoutburst and 8 outbursts
  of the 45-day supercycle of the dwarf nova V1159 Ori was obtained in
  Feb-Mar 1996. The use of RXTE, ROSAT, IUE, and EUVE satellites, combined
  with ground-based optical photometry and spectroscopy, provided a broad
  picture of the accretion disk at different states. Results include
  an inverse correlation of the X-ray with the UV/optical fluxes, an
  outflowing wind during all outbursts, and large changes in the disk
  spectrum on time scales of less than a day. These results are compared
  to other dwarf novae and general theories of dwarf nova outbursts.

Title: A Grid of Relativistic, Non-LTE Accretion Disk Models for
    Spectral Fitting of Black Hole Binaries
Authors: Davis, Shane W.; Hubeny, Ivan
Bibcode: 2006ApJS..164..530D
Altcode: 2006astro.ph..2499D
  Self-consistent vertical structure models together with non-LTE
  radiative transfer should produce spectra from accretion disks around
  black holes, which differ from multitemperature blackbodies at levels
  that may be observed. High-resolution, high signal-to-noise observations
  warrant spectral modeling that both accounts for relativistic effects
  and treats the physics of radiative transfer in detail. In Davis et
  al. we presented spectral models that accounted for non-LTE effects,
  Compton scattering, and the opacities due to ions of abundant
  metals. Using a modification of this method, we have tabulated
  spectra for black hole masses typical of Galactic binaries. We make
  them publicly available for spectral fitting as an XSPEC model. These
  models represent the most complete realization of standard accretion
  disk theory to date. Thus, they are well suited both for testing
  the theory's applicability to observed systems and for constraining
  properties of the black holes, including their spins.

Title: New Praesepe white dwarfs and the initial mass-final mass
    relation
Authors: Dobbie, P. D.; Napiwotzki, R.; Burleigh, M. R.; Barstow,
   M. A.; Boyce, D. D.; Casewell, S. L.; Jameson, R. F.; Hubeny, I.;
   Fontaine, G.
Bibcode: 2006MNRAS.369..383D
Altcode: 2006astro.ph..3314D
  We report the spectroscopic confirmation of four further white dwarf
  members of Praesepe. This brings the total number of confirmed white
  dwarf members to 11, making this the second largest collection of
  these objects in an open cluster identified to date. This number is
  consistent with the high-mass end of the initial mass function of
  Praesepe being Salpeter in form. Furthermore, it suggests that the
  bulk of Praesepe white dwarfs did not gain a substantial recoil kick
  velocity from possible asymmetries in their loss of mass during the
  asymptotic giant branch phase of evolution. By comparing our estimates
  of the effective temperatures and the surface gravities of WD0833+194,
  WD0840+190, WD0840+205 and WD0843+184 to modern theoretical evolutionary
  tracks, we have derived their masses to be in the range 0.72-0.76
  M<SUB>solar</SUB> and their cooling ages ~300 Myr. For an assumed
  cluster age of 625 +/- 50 Myr, the inferred progenitor masses are
  between 3.3 and 3.5 M<SUB>solar</SUB>. Examining these new data in the
  context of the initial mass-final mass relation, we find that it can be
  adequately represented by a linear function (a<SUB>0</SUB> = 0.289 +/-
  0.051,a<SUB>1</SUB> = 0.133 +/- 0.015) over the initial mass range 2.7-6
  M<SUB>solar</SUB>. Assuming an extrapolation of this relation to larger
  initial masses is valid and adopting a maximum white dwarf mass of 1.3
  M<SUB>solar</SUB>, our results support a minimum mass for core-collapse
  supernovae progenitors in the range ~6.8-8.6 M<SUB>solar</SUB>.

Title: L and T Dwarf Models and the L to T Transition
Authors: Burrows, Adam; Sudarsky, David; Hubeny, Ivan
Bibcode: 2006ApJ...640.1063B
Altcode: 2005astro.ph..9066B
  Using a model for refractory clouds, a novel algorithm for handling
  them, and the latest gas-phase molecular opacities, we have produced a
  new series of L and T dwarf spectral and atmosphere models as a function
  of gravity and metallicity, spanning the T<SUB>eff</SUB> range from 2200
  to 700 K. The correspondence with observed spectra and infrared colors
  for early and mid-L dwarfs and for mid- to late T dwarfs is good. We
  find that the width in infrared color-magnitude diagrams of both the T
  and L dwarf branches is naturally explained by reasonable variations
  in gravity and therefore that gravity is the ``second parameter'' of
  the L-T dwarf sequence. We investigate the dependence of theoretical
  dwarf spectra and color-magnitude diagrams on various cloud properties,
  such as particle size and cloud spatial distribution. In the region
  of the L--&gt;T transition, we find that no single combination of
  cloud particle size and gravity can be made to fit all the observed
  data. Our results suggest that current ignorance of detailed cloud
  meteorology renders ambiguous the extraction of various physical
  quantities such as T<SUB>eff</SUB> and gravity for mid-L to early T
  dwarfs. Nevertheless, for decreasing T<SUB>eff</SUB>, we capture with
  some accuracy the major spectral features and signatures observed. We
  speculate that the subdwarf branch of the L dwarfs would be narrower in
  effective temperature and that for low enough metallicity the L dwarfs
  would disappear altogether as a spectroscopic class. Furthermore, we
  note that the new, lower solar oxygen abundances of Allende-Prieto
  and coworkers produce better fits to brown dwarf data than do the
  older values. Finally, we discuss various issues in cloud physics and
  modeling and speculate on how a better correspondence between theory
  and observation in the problematic L--&gt;T transition region could
  be achieved.

Title: FUSE and HST STIS Far-Ultraviolet Observations of AM Herculis
    in an Extended Low State
Authors: Gänsicke, Boris T.; Long, Knox S.; Barstow, Martin A.;
   Hubeny, Ivan
Bibcode: 2006ApJ...639.1039G
Altcode: 2005astro.ph.11100G
  We have obtained FUSE and HST STIS time-resolved spectroscopy of the
  Polar AM Herculis during a deep low state. The spectra are entirely
  dominated by the emission of the white dwarf. Both the far-ultraviolet
  (FUV) flux and the spectral shape vary substantially over the orbital
  period, with maximum flux occurring at the same phase as during the
  high state. The variations are due to the presence of a hot spot
  on the white dwarf, which we model quantitatively. The white dwarf
  parameters can be determined from a spectral fit to the faint-phase
  data, when the hot spot is self-eclipsed. Adopting the distance
  of 79<SUP>+8</SUP><SUB>-6</SUB> pc determined by Thorstensen,
  we find an effective temperature of 19,800+/-700 K and a mass of
  M<SUB>WD</SUB>=0.78+0.12-0.17 M<SUB>solar</SUB>. The hot spot has
  a lower temperature than during the high state, ~34,000-40,000 K,
  but covers a similar area, ~10% of the white dwarf surface. Low-state
  FUSE and STIS spectra taken during four different epochs in 2002-2003
  show no variation of the FUV flux level or spectral shape, implying
  that the white dwarf temperature and the hot spot temperature, size,
  and location do not depend on the amount of time the system has spent
  in the low state. Possible explanations are ongoing accretion at a low
  level or deep heating; both alternatives have some weaknesses, which we
  discuss. No photospheric metal absorption lines are detected in the FUSE
  and STIS spectra, suggesting that the average metal abundances in the
  white dwarf atmosphere are lower than ~10<SUP>-3</SUP> times their solar
  values. <P />Based on observations made with the NASA/ESA Hubble Space
  Telescope, obtained at the Space Telescope Science Institute, which is
  operated by the Association of Universities for Research in Astronomy,
  Inc., under NASA contract NAS 5-26555, and on observations made with the
  NASA-CNES-CSA Far-Ultraviolet Spectroscopic Explorer. FUSE is operated
  for NASA by the Johns Hopkins University under NASA contract NAS5-32985.

Title: Fundamental Properties of O-Type Stars
Authors: Heap, Sara R.; Lanz, Thierry; Hubeny, Ivan
Bibcode: 2006ApJ...638..409H
Altcode: 2004astro.ph.12345H
  We present a comprehensive analysis of high-resolution, far-ultraviolet
  HST STIS, FUSE, and optical spectra of 18 O stars in the Small
  Magellanic Cloud. Our analysis is based on the OSTAR2002 grid of
  NLTE metal-line-blanketed model atmospheres calculated with our
  code TLUSTY. We systematically explore and present the sensitivity
  of various UV and optical lines to different stellar parameters. We
  have obtained consistent fits of the UV and the optical spectrum to
  derive the effective temperature, surface gravity, surface composition,
  and microturbulent velocity of each star. Stellar radii, masses, and
  luminosities follow directly. For stars of the same spectral subtype,
  we find a general good agreement between effective temperature
  determinations obtained with TLUSTY, CMFGEN, and FASTWIND models,
  which are all lower than the standard T<SUB>eff</SUB> calibration
  of O stars. We propose a new calibration between the spectral type
  and effective temperature based on our results from UV metal lines,
  as well as optical hydrogen and helium lines. The lower effective
  temperatures translate into ionizing luminosities that are smaller
  by a factor of 3 compared to luminosities inferred from previous
  standard calibrations. The chemical composition analysis reveals
  that the surface of about 80% of the program stars is moderately to
  strongly enriched in nitrogen, while showing the original helium,
  carbon, and oxygen abundances. Our results support the new stellar
  evolution models that predict that the surface of fast rotating
  stars becomes nitrogen-rich during the main-sequence phase because of
  rotationally induced mixing. Enrichment factors are, however, larger
  than predicted by stellar evolution models. Most stars exhibit the
  ``mass discrepancy'' problem, which we interpret as a result of fast
  rotation that lowers the measured effective gravity. Nitrogen enrichment
  and low spectroscopic masses are therefore two manifestations of fast
  rotation. Our study thus emphasizes the importance of rotation in
  our understanding of the properties of massive stars and provides a
  framework for investigating populations of low-metallicity massive
  stars at low and high redshifts. <P />Based on observations with
  the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope
  Science Institute, which is operated by the Association of Universities
  for Research in Astronomy, Inc., under NASA contract NAS5-2655. Also
  based on observations made with the NASA-CNES-CSA Far Ultraviolet
  Spectroscopic Explorer, which is operated for NASA by Johns Hopkins
  University under NASA contract NAS5-32985.

Title: Radiative Transfer in Astrophysical Applications
Authors: Hubeny, I.
Bibcode: 2006cmt..conf...15H
Altcode:
  No abstract at ADS

Title: Non-LTE Line-Blanketed Model Atmospheres of B-type Stars
Authors: Lanz, T.; Hubeny, I.
Bibcode: 2005AAS...20718221L
Altcode: 2005BAAS...37.1467L
  We present an extension of our OSTAR2002 grid of NLTE model atmospheres
  to B-type stars. We have calculated over 1,300 metal line-blanketed,
  NLTE, plane-parallel, hydrostatic model atmospheres for the basic
  parameters appropriate to B stars. The grid covers 16 effective
  temperatures from 15,000 to 30,000 K, with 1000 K steps, 13 surface
  gravities, log g≤ 4.75 down to the Eddington limit, and 5 compositions
  (2, 1, 0.5, 0.2, and 0.1 times solar). We have adopted a microturbulent
  velocity of 2 km/s for all models. In the lower surface gravity range
  (log g≤ 3.0), we supplemented the main grid with additional model
  atmospheres accounting for higher microtutbulent velocity (10 km/s)
  and for alterated surface composition (He and N-rich, C-deficient),
  as observed in B supergiants. The models incorporate basically all
  known atomic levels of 46 ions of H, He, C, N, O, Ne, Mg, Al, Si, S,
  and Fe, which are grouped into 1127 superlevels. Models and spectra
  will be available at our Web site, http://nova.astro.umd.edu.

Title: Photospheric phosphorus in the FUSE spectra of GD71 and two
    similar DA white dwarfs
Authors: Dobbie, P. D.; Barstow, M. A.; Hubeny, I.; Holberg, J. B.;
   Burleigh, M. R.; Forbes, A. E.
Bibcode: 2005MNRAS.363..763D
Altcode: 2005MNRAS.tmp..867D; 2005astro.ph..7638D
  We report the detection, from the Far Ultraviolet Spectroscopic
  Explorer (FUSE) data, of phosphorus in the atmospheres of GD71 and
  two similar DA white dwarfs. This is the first detection of a trace
  metal in the photosphere of the spectrophotometric standard star
  GD71. Collectively, these objects represent the coolest DA white dwarfs
  in which photospheric phosphorus has been observed. We use a grid of
  homogeneous non-local thermodynamic equilibrium synthetic spectra to
  measure abundances of [P/H]=-8.57<SUP>+0.09</SUP><SUB>-0.13</SUB>,
  -8.70<SUP>+0.23</SUP><SUB>-0.37</SUB> and
  -8.36<SUP>+0.14</SUP><SUB>-0.19</SUB> in GD71, RE J1918+595 and RE
  J0605-482 respectively. At the observed level we find that phosphorus
  has no significant impact on the overall energy distribution of
  GD71. We explore possible mechanisms responsible for the presence of
  this element in these stars, concluding that the most likely is an
  interplay between radiative levitation and gravitational settling,
  possibly modified by weak mass loss.

Title: Heavy element abundances in DAO white dwarfs measured from
    FUSE data
Authors: Good, S. A.; Barstow, M. A.; Burleigh, M. R.; Dobbie, P. D.;
   Holberg, J. B.; Hubeny, I.
Bibcode: 2005MNRAS.363..183G
Altcode: 2005MNRAS.tmp..762G; 2005astro.ph..7341G
  We present heavy element abundance measurements for 16 DAO white
  dwarfs, determined from Far-Ultraviolet Spectroscopic Explorer (FUSE)
  spectra. Evidence of absorption by heavy elements was found in the
  spectra of all the objects. Measurements were made using models that
  adopted the temperatures, gravities and helium abundances determined
  from both optical and FUSE data by Good et al. It was found that,
  when using the values for the parameters measured from optical data,
  the carbon abundance measurements follow and extend a similar trend of
  increasing abundance with temperature for DA white dwarfs, as discovered
  by Barstow et al. However, when the FUSE measurements are used, the DAO
  abundances no longer join this trend since the temperatures are higher
  than the optical measures. Silicon abundances were found to increase
  with temperature, but no similar trend was identified in the nitrogen,
  oxygen, iron or nickel abundances, and no dependence on gravity or
  helium abundances was noted. However, the models were not able to
  reproduce the observed silicon and iron line strengths satisfactorily in
  the spectra of half of the objects, and the oxygen features of all but
  three. Despite the different evolutionary paths that the types of DAO
  white dwarfs are thought to evolve through, their abundances were not
  found to vary significantly, apart from for the silicon abundances. <P
  />Abundances measured when the FUSE-derived values of temperature,
  gravity and helium abundance were adopted were, in general, a factor
  1-10 higher than those determined when the optical measure of those
  parameters was used. Satisfactory fits to the absorption lines were
  achieved in an approximately equal number. The models that used the
  FUSE-determined parameters seemed better at reproducing the strength of
  the nitrogen and iron lines, while for oxygen the optical parameters
  were better. For the three objects whose temperature measured from
  FUSE data exceeds 120000 K, the carbon, nitrogen and oxygen lines
  were too weak in the models that used the FUSE parameters. However,
  the model that used the optical parameters also did not reproduce the
  strength of all the lines accurately.

Title: Hubble Space Telescope spectroscopy of the Balmer lines in
    Sirius B<SUP>*</SUP>
Authors: Barstow, M. A.; Bond, Howard E.; Holberg, J. B.; Burleigh,
   M. R.; Hubeny, I.; Koester, D.
Bibcode: 2005MNRAS.362.1134B
Altcode: 2005astro.ph..6600B; 2005MNRAS.tmp..739B
  Sirius B is the nearest and brightest of all white dwarfs, but it is
  very difficult to observe at visible wavelengths due to the overwhelming
  scattered light contribution from Sirius A. However, from space we can
  take advantage of the superb spatial resolution of the Hubble Space
  Telescope (HST) to resolve the A and B components. Since the closest
  approach in 1993, the separation between the two stars has become
  increasingly favourable and we have recently been able to obtain a
  spectrum of the complete Balmer line series for Sirius B using the
  HST Space Telescope Imaging Spectrograph (STIS). The quality of the
  STIS spectra greatly exceeds that of previous ground-based spectra,
  and can be used to provide an important determination of the stellar
  temperature (T<SUB>eff</SUB>= 25193 K) and gravity (logg= 8.556). In
  addition, we have obtained a new, more accurate, gravitational
  redshift of 80.42 +/- 4.83 km s<SUP>-1</SUP> for Sirius B. Combining
  these results with the photometric data and the Hipparcos parallax,
  we obtain new determinations of the stellar mass for comparison
  with the theoretical mass-radius relation. However, there are some
  disparities between the results obtained independently from logg and
  the gravitational redshift which may arise from flux losses in the
  narrow 50 × 0.2 arcsec<SUP>2</SUP> slit. Combining our measurements
  of T<SUB>eff</SUB> and logg with the Wood evolutionary mass-radius
  relation, we obtain a best estimate for the white dwarf mass of
  0.978 M<SUB>solar</SUB>. Within the overall uncertainties, this is in
  agreement with a mass of 1.02 M<SUB>solar</SUB> obtained by matching
  our new gravitational redshift to the theoretical mass-radius relation.

Title: High-resolution extreme ultraviolet spectroscopy of G191-B2B:
    structure of the stellar photosphere and the surrounding interstellar
    medium
Authors: Barstow, M. A.; Cruddace, R. G.; Kowalski, M. P.; Bannister,
   N. P.; Yentis, D.; Lapington, J. S.; Tandy, J. A.; Hubeny, I.; Schuh,
   S.; Dreizler, S.; Barbee, T. W.
Bibcode: 2005MNRAS.362.1273B
Altcode: 2005MNRAS.tmp..749B
  We have continued our detailed analysis of the high-resolution (R=
  4000) spectroscopic observation of the DA white dwarf G191-B2B,
  obtained by the Joint Astrophysical Plasmadynamic Experiment (J-PEX)
  normal incidence sounding rocket-borne telescope, comparing the
  observed data with theoretical predictions for both homogeneous and
  stratified atmosphere structures. We find that the former models
  give the best agreement over the narrow waveband covered by J-PEX,
  in conflict with what is expected from previous studies of the lower
  resolution but broader wavelength coverage Extreme Ultraviolet Explorer
  spectra. We discuss the possible limitations of the atomic data and
  our understanding of the stellar atmospheres that might give rise to
  this inconsistency. In our earlier study, we obtained an unusually
  high ionization fraction for the ionized HeII present along the line
  of sight to the star. In the present paper, we obtain a better fit
  when we assume, as suggested by Space Telescope Imaging Spectrograph
  results, that this HeII resides in two separate components. When one
  of these is assigned to the local interstellar cloud, the implied He
  ionization fraction is consistent with measurements along other lines
  of sight. However, the resolving power and signal-to-noise available
  from the instrument configuration used in this first successful J-PEX
  flight are not sufficient to clearly identify and prove the existence
  of the two components.

Title: A near-IR spectrum of the DO white dwarf <ASTROBJ>RE
    J0503-285</ASTROBJ>
Authors: Dobbie, P. D.; Burleigh, M. R.; Levan, A. J.; Barstow, M. A.;
   Napiwotzki, R.; Hubeny, I.
Bibcode: 2005A&A...439.1159D
Altcode: 2005astro.ph..6384D
  We present a near-IR spectroscopic analysis of the intriguing DO white
  dwarf RE J0503-285. The IR spectrum fails to reveal evidence of the
  presence of a spatially unresolved, cool, late-type companion. Hence
  we have placed an approximate limit on the spectral-type and mass of a
  putative companion (later than M8, M&lt;0.085~M<SUB>⊙</SUB>). This
  result rules out ongoing interaction between the white dwarf and a
  close companion with M≥0.085~M<SUB>⊙</SUB> as responsible for
  the discrepancies between the observed photospheric abundances and
  model predictions. As the possibility remains that there is a cooler
  companion lying beyond the detection threshold of this study we use
  our modelling to estimate the improvement in sensitivity offered by
  a Spitzer observation.

Title: X-ray Heated Black Hole Accretion Discs
Authors: Wickramasinghe, D.; Hubeny, I.
Bibcode: 2005ASPC..330..219W
Altcode:
  The response of the disc to external irradiation depends on the
  importance of the irradiation flux relative to the viscous flux, and
  on the details of the incident spectrum; the higher energy photons will
  preferentially Compton scatter and heat/cool the disc, while the lower
  energy photons will be mainly photo absorbed and re-emitted. Irradiation
  with a black body spectrum at temperatures appropriate to the inner
  regions of the disc generally results in a temperature inversion in
  the upper disc atmosphere at all disc radii. A general characteristic
  of all models is that as the irradiation flux increases relative to the
  viscously generated flux, and the effects of heating penetrates to the
  disc mid plane, the temperature profile at large optical depths becomes
  flatter. In addition, irradiation reduces the continuum jumps and makes
  the spectrum more black body like. For moderate irradiation, a Compton
  reflection peak develops at frequencies corresponding approximately
  to the peak of the irradiating flux. This is seen as a flux excess
  over the thermal emission that would normally be expected from the
  heated disc if the effects of scattering were ignored. In the limit of
  strong irradiation, a saturated inverse Compton spectrum develops with
  a high energy Wien tail. The detection of a Compton reflection peak,
  and a study of its spectral characteristics, will provide a strong
  diagnostic on the nature of the irradiating source. H<SUB>α</SUB>
  line profiles are also presented.

Title: Mass Loss for Highly-Irradiated Giant Planets
Authors: Hubbard, W. B.; Burrows, A.; Hubeny, I.; Sudarsky, D.;
   Hattori, M. F.
Bibcode: 2005DPS....37.3105H
Altcode: 2005BAAS...37..684H
  We present calculations for the surviving mass of highly-irradiated
  extrasolar giant planets (EGPs) at orbital semimajor axes ranging
  from 0.023 to 0.057 AU using a generalized scaled theory for mass
  loss, together with new surface-condition grids for hot EGPs and a
  consistent treatment of tidal truncation. <P />Available theoretical
  estimates for the rate of energy-limited hydrogen escape from
  giant-planet atmospheres range over four orders of magnitude, when
  one holds planetary mass, composition, and irradiation constant. Yelle
  (Icarus 170, 167-179, 2004) predicts the lowest escape rate. Baraffe
  et al. (A&amp;A 419, L13-L16, 2004) predict the highest rate, based on
  the theory of Lammer et al. (ApJ 598, L121-L124, 2003). Scaling the
  theory of Watson et al. (Icarus 48, 150-166, 1981) to parameters for
  a highly-irradiated exoplanet, we find an intermediate escape rate,
  ∼ 10<SUP>2</SUP> higher than Yelle's but ∼ 10<SUP>2</SUP> lower
  than Baraffe's. <P />With the scaled Watson theory and the scaled
  Yelle theory we find modest mass loss, occurring early in the history
  of a hot EGP. Particularly for the Yelle theory, the effect of tidal
  truncation sets the minimum mass limit, well below a Saturn mass for
  the distances investigated. This contrasts with the Baraffe model,
  where hot EGPs are claimed to be remnants of much more massive bodies,
  originally several times Jupiter and still losing substantial mass
  fractions at present. <P />Supported by NASA Grant NAG5-13775 (PGG)
  and NASA Grant NNG04GL22G (ATP).

Title: Effects of mass loss for highly-irradiated giant planets
Authors: Hubbard, W. B.; Hattori, M. F.; Burrows, A.; Hubeny, I.;
   Sudarsky, D.
Bibcode: 2005astro.ph..8591H
Altcode:
  We present calculations for the evolution and surviving mass of
  highly-irradiated extrasolar giant planets (EGPs) at orbital semimajor
  axes ranging from 0.023 to 0.057 AU using a generalized scaled theory
  for mass loss, together with new surface-condition grids for hot EGPs
  and a consistent treatment of tidal truncation. Theoretical estimates
  for the rate of energy-limited hydrogen escape from giant-planet
  atmospheres differ by two orders of magnitude, when one holds planetary
  mass, composition, and irradiation constant. Baraffe et al. (2004,
  A&amp;A 419, L13-L16) predict the highest rate, based on the theory
  of Lammer et al. (2003, Astrophys. J. 598, L121-L124). Scaling the
  theory of Watson et al. (1981, Icarus 48, 150-166) to parameters for
  a highly-irradiated exoplanet, we find an escape rate ~102 lower than
  Baraffe's. With the scaled Watson theory we find modest mass loss,
  occurring early in the history of a hot EGP. In this theory, mass
  loss including the effect of Roche-lobe overflow becomes significant
  primarily for masses below a Saturn mass, for semimajor axes = 0.023
  AU. This contrasts with the Baraffe model, where hot EGPs are claimed
  to be remnants of much more massive bodies, originally several times
  Jupiter and still losing substantial mass fractions at present.

Title: HST Observations of the Sirius B Balmer Lines
Authors: Barstow, M. A.; Burleigh, M. R.; Holberg, J. B.; Hubeny,
   I.; Bond, H. E.; Koester, D.
Bibcode: 2005ASPC..334..175B
Altcode:
  For most of the lifetime of the Hubble Space Telescope (HST), it has
  not been possible to observe Sirius B spectroscopically at visible
  wavelengths due to the overwhelming scattered light contribution
  from Sirius A. However, as the separation between the two stars is
  becoming larger we have been able to obtain a spectrum of the complete
  Balmer line series for Sirius B. This is the first such spectrum to be
  obtained, apart from old ground-based photographic spectra, and can be
  used to provide an important determination of the stellar temperature
  and gravity.

Title: Phase Functions and Light Curves of Wide-Separation Extrasolar
    Giant Planets
Authors: Sudarsky, David; Burrows, Adam; Hubeny, Ivan; Li, Aigen
Bibcode: 2005ApJ...627..520S
Altcode: 2005astro.ph..1109S
  We calculate self-consistent extrasolar giant planet (EGP) phase
  functions and light curves for orbital distances ranging from 0.2 to
  15 AU. We explore the dependence on wavelength, cloud condensation,
  and Keplerian orbital elements. We find that the light curves of
  EGPs depend strongly on wavelength, the presence of clouds, and
  cloud particle sizes. Furthermore, the optical and infrared colors
  of most EGPs are phase-dependent, tending to be reddest at crescent
  phases in V-R and R-I. Assuming circular orbits, we find that at
  optical wavelengths most EGPs are 3-4 times brighter near full phase
  than near greatest elongation for highly inclined (i.e., close to
  edge-on) orbits. Furthermore, we show that the planet/star flux ratios
  depend strongly on the Keplerian elements of the orbit, particularly
  inclination and eccentricity. Given a sufficiently eccentric orbit,
  an EGP's atmosphere may make periodic transitions from cloudy to
  cloud-free, an effect that may be reflected in the shape and magnitude
  of the planet's light curve. Such elliptical orbits also introduce an
  offset between the time of the planet's light-curve maximum and the
  time of full planetary phase, and for some sets of orbital parameters,
  this light-curve maximum can be a steeply increasing function of
  eccentricity. We investigate the detectability of EGPs by proposed
  space-based direct-imaging instruments.

Title: Searching for the Donor Star in Close Binary Supersoft Sources
Authors: Lanz, Thierry; Audard, Marc; Hubeny, Ivan; Paerels, Frits
Bibcode: 2005sptz.prop20130L
Altcode:
  The identification of Type Ia Supernova progenitors still remains
  elusive. The most promising channel to form SNe Ia involves accreting
  white dwarfs (WDs) in close binary systems. The hot WDs sustain
  steady nuclear burning and are observed as ultrasoft X-ray sources. The
  companions have remained until now undetected because the UV and optical
  spectrum is dominated by the emission from the accretion disk around
  the WDs. At present, these close binary supersoft sources (CBSS) have
  not been observed in the infrared, with the single exception of near-IR
  photometry of the Galactic CBSS QR And that provides the first hint
  of the secondary. Because of the general lack of a direct detection,
  the nature of the donor stars in these systems is still debated. By
  combining ultraviolet and optical SEDs with Spitzer observations of 4
  CBSS in the mid-infrared, we will be able to definitively identify the
  nature of the donor stars in CBSS systems, as well as determining the
  size of the accretion disks. We propose to observe eclipsing systems
  at different phases to disentangle the contribution of the companions
  from the emission of the disks. Spitzer observations of CBSS will
  therefore represent a significant step forward in characterizing the
  binary systems that are best candidates for becoming SNe Ia.

Title: Non-LTE Spectra of Accretion Disks around Intermediate-Mass
    Black Holes
Authors: Hui, Yawei; Krolik, Julian H.; Hubeny, Ivan
Bibcode: 2005ApJ...625..913H
Altcode: 2005astro.ph..2355H
  We have calculated the structures and the emergent spectra of
  stationary, geometrically thin accretion disks around 100 and 1000
  M<SUB>solar</SUB> black holes in both the Schwarzschild and extreme
  Kerr metrics. Equations of radiative transfer, hydrostatic equilibrium,
  energy balance, ionization equilibrium, and statistical equilibrium are
  solved simultaneously and consistently. The six most astrophysically
  abundant elements (H, He, C, N, O, and Fe) are included, as well
  as energy transfer by Comptonization. The observed spectrum as a
  function of viewing angle is computed, incorporating all general
  relativistic effects. We find that, in contrast with the predictions
  of the commonly used multicolor disk (MCD) model, opacity associated
  with photoionization of heavy elements can significantly alter the
  spectrum near its peak. These ionization edges can create spectral
  breaks visible in the spectra of slowly spinning black holes viewed
  from almost all angles and in the spectra of rapidly spinning black
  holes seen approximately pole-on. For fixed mass and accretion rate
  relative to Eddington, both the black hole spin and the viewing angle
  can significantly shift the observed peak energy of the spectrum,
  particularly for rapid spin viewed obliquely or edge-on. We present
  a detailed test of the approximations made in various forms of the
  MCD model. Linear limb-darkening is confirmed to be a reasonable
  approximation for the integrated flux but not for many specific
  frequencies of interest.

Title: A non-LTE analysis of the spectra of two narrow lined main
    sequence stars in the SMC
Authors: Hunter, I.; Dufton, P. L.; Ryans, R. S. I.; Lennon, D. J.;
   Rolleston, W. R. J.; Hubeny, I.; Lanz, T.
Bibcode: 2005A&A...436..687H
Altcode: 2005astro.ph..3662H
  An analysis of high-resolution VLT/UVES spectra of two B-type main
  sequence stars, NGC 346-11 and AV 304, in the Small Magellanic Cloud
  (SMC), has been undertaken, using the non-LTE tlusty model atmospheres
  to derive the stellar parameters and chemical compositions of each
  star. The chemical compositions of the two stars are in reasonable
  agreement. Moreover, our stellar analysis agrees well with earlier
  analyses of H II regions. The results derived here should be
  representative of the current base-line chemical composition of the
  SMC interstellar medium as derived from B-type stars.

Title: A Theoretical Interpretation of the Measurements of the
    Secondary Eclipses of TrES-1 and HD 209458b
Authors: Burrows, A.; Hubeny, I.; Sudarsky, D.
Bibcode: 2005ApJ...625L.135B
Altcode: 2005astro.ph..3522B
  We calculate the planet-to-star flux density ratios as a function
  of wavelength from 0.5 to 25 μm for the transiting extrasolar
  giant planets TrES-1 and HD 209458b and compare them with the recent
  Spitzer/IRAC-MIPS secondary eclipse data in the 4.5, 8.0, and 24 μm
  bands. With only three data points and generic calibration issues,
  detailed conclusions are difficult, but inferences regarding atmospheric
  composition, temperature, and global circulation can be made. Our
  models reproduce the observations reasonably well, but not perfectly,
  and we speculate on the theoretical consequences of variations around
  our baseline models. One preliminary conclusion is that we may be seeing
  in the data indications that the day side of a close-in extrasolar
  giant planet is brighter in the mid-infrared than its night side,
  unlike Jupiter and Saturn. This correspondence will be further tested
  when the data anticipated in other Spitzer bands are acquired, and we
  make predictions for what those data may show.

Title: MV Lyrae in Low, Intermediate, and High States
Authors: Linnell, Albert P.; Szkody, Paula; Gänsicke, Boris; Long,
   Knox S.; Sion, Edward M.; Hoard, D. W.; Hubeny, Ivan
Bibcode: 2005ApJ...624..923L
Altcode: 2006astro.ph.12696L
  Archival IUE spectra of the VY Sculptoris system MV Lyrae, taken during
  an intermediate state, can be best fit by an isothermal accretion disk
  extending half-way to the tidal cutoff radius. In contrast, a recent
  HST spectrum, while MV Lyr was in a high state, can be best fit with
  a standard T(R) profile for an accretion disk extending from an inner
  truncation radius to an intermediate radius with an isothermal accretion
  disk beyond. These fits use component-star parameters determined from
  a study of MV Lyr in a low state. Model systems containing accretion
  disks with standard T(R) profiles have continua that are too blue. The
  observed high-state absorption-line spectrum exhibits excitation
  higher than provided by the T(R) profile, indicating likely line
  formation in a high-temperature region extending vertically above
  the accretion disk. The absorption lines show a blueshift and line
  broadening corresponding to formation in a low-velocity wind apparently
  coextensive with the high-temperature region. Lines of N V, Si IV, C IV,
  and He II are anomalously strong relative to our synthetic spectra,
  indicating possible composition effects, but unmodeled excitation
  effects could also produce the anomalies. An analysis of a low state
  of MV Lyr, considered in an earlier study and extended in this paper,
  sets a limit of 2500 K for the T<SUB>eff</SUB> of an accretion disk
  that may be present in the low state. This limit is in conflict with
  two recent models of the VY Sculptoris phenomenon. <P />Based on
  observations made with the NASA/ESA Hubble Space Telescope, obtained
  at the Space Telescope Science Institute, which is operated by the
  Association of Universities for Research in Astronomy, Inc., under
  NASA contract NAS5-26555, and with the Apache Point Observatory 3.5 m
  telescope, which is operated by the Astrophysical Research Corporation.

Title: B-type supergiants in the SMC: Chemical compositions and
    comparison of static and unified models
Authors: Dufton, P. L.; Ryans, R. S. I.; Trundle, C.; Lennon, D. J.;
   Hubeny, I.; Lanz, T.; Allende Prieto, C.
Bibcode: 2005A&A...434.1125D
Altcode: 2004astro.ph.12367D
  High-resolution UCLES/AAT spectra are presented for nine B-type
  supergiants in the SMC, chosen on the basis that they may show
  varying amounts of nuclear-synthetically processed material mixed to
  their surface. These spectra have been analysed using a new grid of
  approximately 12 000 non-LTE line blanketed tlusty model atmospheres
  to estimate atmospheric parameters and chemical composition. The
  abundance estimates for O, Mg and Si are in excellent agreement with
  those deduced from other studies, whilst the low estimate for C may
  reflect the use of the C II doublet at 4267 Å. The N estimates
  are approximately an order of magnitude greater than those found
  in unevolved B-type stars or H II regions but are consistent with
  the other estimates in AB-type supergiants. These results have been
  combined with results from a unified model atmosphere analysis of
  UVES/VLT spectra of B-type supergiants (Trundle et al. 2004, A&amp;A,
  417, 217) to discuss the evolutionary status of these objects. For
  two stars that are in common with those discussed by Trundle et al.,
  we have undertaken a careful comparison in order to try to understand
  the relative importance of the different uncertainties present in
  such analyses, including observational errors and the use of static
  or unified models. We find that even for these relatively luminous
  supergiants, tlusty models yield atmospheric parameters and chemical
  compositions similar to those deduced from the unified code fastwind.

Title: A Study of the Near-Ultraviolet Spectrum of Vega
Authors: García-Gil, Alejandro; García López, Ramón J.; Allende
   Prieto, Carlos; Hubeny, Ivan
Bibcode: 2005ApJ...623..460G
Altcode: 2005astro.ph..1213G
  UV, optical, and near-IR spectra of Vega have been combined to test
  our understanding of stellar atmospheric opacities and to examine the
  possibility of constraining chemical abundances from low-resolution
  UV fluxes. We have carried out a detailed analysis assuming local
  thermodynamic equilibrium (LTE) to identify the most important
  contributors to the UV continuous opacity: H, H<SUP>-</SUP>, C I, and
  Si II. Our analysis also assumes that Vega is spherically symmetric
  and that its atmosphere is well described with the plane-parallel
  approximation. By comparing observations and computed fluxes, we have
  been able to discriminate between two different flux scales that have
  been proposed, the IUE-INES and the HST scales; we favor the latter. The
  effective temperature and angular diameter derived from the analysis
  of observed optical and near-UV spectra are in very good agreement
  with previous determinations based on different techniques. The silicon
  abundance is poorly constrained by the UV observations of the continuum
  and strong lines, but the situation is more favorable for carbon, and
  the abundances inferred from the UV continuum and optical absorption
  lines are in good agreement. Some spectral intervals in the UV spectrum
  of Vega poorly reproduced by the calculations are likely affected
  by deviations from LTE, but we conclude that our understanding of UV
  atmospheric opacities is fairly complete for early A-type stars.

Title: Relativistic Accretion Disk Models of High-State Black Hole
    X-Ray Binary Spectra
Authors: Davis, Shane W.; Blaes, Omer M.; Hubeny, Ivan; Turner, Neal J.
Bibcode: 2005ApJ...621..372D
Altcode: 2004astro.ph..8590D
  We present calculations of non-LTE, relativistic accretion disk models
  applicable to the high/soft state of black hole X-ray binaries. We
  include the effects of thermal Comptonization and bound-free and
  free-free opacities of all abundant ion species. Taking into account
  the relativistic propagation of photons from the local disk surface to
  an observer at infinity, we present spectra calculated for a variety
  of accretion rates, black hole spin parameters, disk inclinations, and
  stress prescriptions. We also consider nonzero inner torques on the
  disk and explore different vertical dissipation profiles, including
  some that are motivated by recent radiation magnetohydrodynamic
  (MHD) simulations of magnetorotational turbulence. Bound-free metal
  opacity generally produces significantly less spectral hardening than
  previous models that only considered Compton scattering and free-free
  opacity. We find that the resulting effective photosphere usually lies
  at a small fraction of the total column depth, producing spectra that
  are remarkably independent of the stress prescription and vertical
  structure assumptions. We provide detailed comparisons between our
  models and the widely used multicolor disk model. Frequency-dependent
  discrepancies exist that may affect the parameters of other spectral
  components when this simpler disk model is used to fit modern X-ray
  data. For a given source, our models predict that the luminosity in the
  high/soft state should approximately scale with the fourth power of the
  empirically inferred maximum temperature, but with a slight hardening
  at high luminosities. This is in good agreement with observations.

Title: A near-infrared spectroscopic search for very-low-mass cool
    companions to notable DA white dwarfs
Authors: Dobbie, P. D.; Burleigh, M. R.; Levan, A. J.; Barstow, M. A.;
   Napiwotzki, R.; Holberg, J. B.; Hubeny, I.; Howell, S. B.
Bibcode: 2005MNRAS.357.1049D
Altcode: 2004astro.ph.12222D; 2005MNRAS.tmp...83D
  We have undertaken a detailed near-infrared spectroscopic
  analysis of eight notable white dwarfs, predominantly of southern
  declination. In each case the spectrum failed to reveal compelling
  evidence for the presence of a spatially unresolved, cool, late-type
  companion. Therefore, we have placed an approximate limit on the
  spectral type of a putative companion to each degenerate. From these
  limits we conclude that if GD659, GD50, GD71 or WD2359-434 possesses
  an unresolved companion then most probably it is substellar in nature
  (M &lt; 0.072 M<SUB>solar</SUB>). Furthermore, any spatially unresolved
  late-type companion to RE J0457-280, RE J0623-374, RE J0723-274 or RE
  J2214-491 most likely has M &lt; 0.082 M<SUB>solar</SUB>. These results
  imply that if weak accretion from a nearby late-type companion is the
  cause of the unusual photospheric composition observed in a number of
  these degenerates then the companions are of very low mass, beyond
  the detection thresholds of this study. Furthermore, these results
  do not contradict a previously noted deficit of very-low-mass stellar
  and brown dwarf companions to main sequence F, G, K and early-M type
  primaries (a&lt;~ 1000 au).

Title: VizieR Online Data Catalog: B-type Supergiants in the SMC
    (Dufton+, 2005)
Authors: Dufton, P. L.; Ryans, R. S. I.; Trundle, C.; Lennon, D. J.;
   Hubeny, I.; Lanz, T.; Allende Prieto, C.
Bibcode: 2005yCat..34341125D
Altcode:
  Table 4 contains the adopted atomic data, equivalent widths and
  abundance estimates for all the metal lines observed in the SMC
  supergiants. It also contains data for the SMC near main sequence
  star AzV 304, which has been used in a differential analysis. <P />(2
  data files).

Title: Quasars and the Big Blue Bump
Authors: Shang, Zhaohui; Brotherton, Michael S.; Green, Richard F.;
   Kriss, Gerard A.; Scott, Jennifer; Quijano, Jessica Kim; Blaes, Omer;
   Hubeny, Ivan; Hutchings, John; Kaiser, Mary Elizabeth; Koratkar,
   Anuradha; Oegerle, William; Zheng, Wei
Bibcode: 2005ApJ...619...41S
Altcode: 2004astro.ph..9697S
  We investigate the ultraviolet-to-optical spectral energy distributions
  of 17 active galactic nuclei (AGNs) using quasi-simultaneous
  spectrophotometry spanning 900-9000 Å (rest frame). We employ
  data from the Far Ultraviolet Spectroscopic Explorer, the Hubble
  Space Telescope, and the 2.1 m telescope at Kitt Peak National
  Observatory. Taking advantage of the short-wavelength coverage, we
  are able to study the so-called big blue bump, the region in which
  the energy output peaks, in detail. Most objects exhibit a spectral
  break around 1100 Å. Although this result is formally associated
  with large uncertainty for some objects, there is strong evidence
  in the data that the far-ultraviolet spectral region is below the
  extrapolation of the near-ultraviolet-optical slope, indicating a
  spectral break around 1100 Å. We compare the behavior of our sample
  to those of non-LTE thin-disk models covering a range in black hole
  mass, Eddington ratio, disk inclination, and other parameters. The
  distribution of ultraviolet-optical spectral indices redward of the
  break and far-ultraviolet indices shortward of the break are in rough
  agreement with the models. However, we do not see a correlation between
  the far-ultraviolet spectral index and the black hole mass, as seen
  in some accretion disk models. We argue that the observed spectral
  break is intrinsic to AGNs, although intrinsic reddening as well
  as Comptonization can strongly affect the far-ultraviolet spectral
  index. We make our data available online in digital format.

Title: Preliminary analysis of an extreme helium sdO star: BD+25 4655
Authors: Budaj, J.; Elkin, V.; Hubeny, I.
Bibcode: 2005astro.ph..1082B
Altcode:
  Preliminary analysis of CCD spectra obtained by the 6m SAO telescope
  is presented. We have used simple H-He NLTE model atmospheres computed
  by TLUSTY to derive the basic parameters of the star.

Title: Constraining Galaxy Formation Epoch
Authors: Yi, S.; Brown, T.; Heap, S.; Hubeny, I.; Landsman, W.; Lanz,
   T.; Sweigart, A.
Bibcode: 2005IAUS..201..536Y
Altcode: 2000IAUS..201E.108Y
  The galaxy formation epoch (z<SUB>f</SUB>) is an important and unique
  product of cosmological models, and thus much effort has been made to
  constrain it. The most direct way of constraining z<SUB>f</SUB> is to
  estimate the ages of bright elliptical galaxies at high redshifts
  arrucately, but it has not been an easy task. We have finally
  reached the stage where the stellar ages can be determined within
  15% uncertainty. Using this advantage, the recent spectral analysis
  of LBDS 53W091 by Spinrad and his collaborators (1997) has suggested
  that this red galaxy at z=1.552 is at least 3.5 Gyr old. This provides
  a significant constraint to cosmology, i.e., z<SUB>f</SUB> &gt; 6.5,
  as LBDS 53W091 is the most distant passiviely evolving galaxy whose UV
  spectrum is available. The results, based on our population synthesis
  models, however, suggest a much smaller age for this galaxy, i.e.,
  1.5 - 2 Gyr. The large discrepancy between their age estimate and ours
  originates from the difference in the model integrated spectra: their
  model spectra are significantly bluer than ours. Such a large difference
  in the models for an apparently simple population is unreasonable. A
  simple test seems to favor our models. If we adopt our age estimate,
  the continuum of this galaxy suggests z<SUB>f</SUB> ≈ 2 - 3. This
  anaysis, when performed to a larger sample, would efficiently constrain
  the global galaxy formation epoch.

Title: Non-LTE Model Atmosphere Analysis of the Large Magellanic
    Cloud Supersoft X-Ray Source CAL 83
Authors: Lanz, Thierry; Telis, Gisela A.; Audard, Marc; Paerels,
   Frits; Rasmussen, Andrew P.; Hubeny, Ivan
Bibcode: 2005ApJ...619..517L
Altcode: 2004astro.ph.10093L
  We present a non-LTE (NLTE) model atmosphere analysis of Chandra High
  Resolution Camera (HRC-S) and Low Energy Transmission Grating (LETG)
  and XMM-Newton Reflection Grating Spectrometer (RGS) spectroscopy
  of the prototypical supersoft source CAL 83 in the Large Magellanic
  Cloud. Taken with a 16 month interval, the Chandra and XMM-Newton
  spectra are very similar. They reveal a very rich absorption-line
  spectrum from the hot white dwarf photosphere but no spectral signatures
  of a wind. We also report a third X-ray off-state during a later Chandra
  observation, demonstrating the recurrent nature of CAL 83. Moreover,
  we found evidence of short-timescale variability in the soft X-ray
  spectrum. We completed the analysis of the LETG and RGS spectra of
  CAL 83 with new NLTE line-blanketed model atmospheres that explicitly
  include 74 ions of the 11 most abundant species. We successfully matched
  the Chandra and XMM-Newton spectra assuming a model composition with
  LMC metallicity. We derived the basic stellar parameters of the hot
  white dwarf, but the current state of atomic data in the soft X-ray
  domain precludes a detailed chemical analysis. We have obtained the
  first direct spectroscopic evidence that the white dwarf is massive
  (M<SUB>WD</SUB>&gt;~1 M<SUB>solar</SUB>). The short timescale of
  the X-ray off-states is consistent with a high white dwarf mass. Our
  analysis thus provides direct support for supersoft sources as likely
  progenitors of Type Ia supernovae (SNe Ia).

Title: Optical Imaging of Extrasolar Giant Planets From Space
Authors: Heap, S. R.; Burrows, A.; Hubeny, I.; Sudarsky, D.
Bibcode: 2004ASPC..321...31H
Altcode:
  We describe initial plans for detecting extrasolar giant planets with
  Eclipse, a 1.8-m space telescope + coronagraph that we will propose
  to NASA in the coming year. Our plans take both theoretical and
  observational constraints into account.

Title: FUSE Observations of Sirius B
Authors: Holberg, J. B.; Barstow, M. A.; Burleigh, M. R.; Kruk, J. W.;
   Hubeny, I.; Koester, D.
Bibcode: 2004AAS...20510303H
Altcode: 2004BAAS...36.1514H
  Observations of the white dwarf Sirius B, obtained in the far
  ultraviolet with the Far Ultraviolet Spectroscopic Explorer Satellite
  (FUSE), reveal the Lyman line region of Sirius B free from significant
  photometric contamination from Sirius A. The FUSE spectra provide a
  new estimate of the white dwarf gravitational redshift based on the
  Lyman lines, as well as Lyman line-based determination of the surface
  gravity, and an estimate of the absolute flux from the white dwarf
  in the FUV. Sirius B is seen to possess strong quasi-molecular Lyman
  line features associated with the Lyman Beta and Lyman Gamma lines. No
  spectroscopic features due to any elements other than hydrogen are
  found in the Sirius B photosphere.

Title: Praesepe and the seven white dwarfs
Authors: Dobbie, P. D.; Pinfield, D. J.; Napiwotzki, R.; Hambly,
   N. C.; Burleigh, M. R.; Barstow, M. A.; Jameson, R. F.; Hubeny, I.
Bibcode: 2004MNRAS.355L..39D
Altcode: 2004astro.ph.10529D; 2004MNRAS.tmp..657D
  We report the discovery, from our preliminary survey of the
  Praesepe open cluster, of two new spectroscopically confirmed
  white dwarf candidate members. We derive the effective
  temperatures and surface gravities of WD0837+218 and WD0837+185
  (LB5959) to be 17845<SUP>+555</SUP><SUB>-565</SUB>K
  and log g = 8.48<SUP>+0.07</SUP><SUB>-0.08</SUB>
  and 14170<SUP>+1380</SUP><SUB>-1590</SUB>K and log g =
  8.46<SUP>+0.15</SUP><SUB>-0.16</SUB>, respectively. Using
  theoretical evolutionary tracks we estimate the masses and cooling
  ages of these white dwarfs to be 0.92 +/- 0.05M<SUB>solar</SUB>
  and 280<SUP>+40</SUP><SUB>-30</SUB> Myr and 0.90 +/- 0.10
  M<SUB>solar</SUB> and 500<SUP>+170</SUP><SUB>-100</SUB> Myr,
  respectively. Adopting reasonable values for the cluster age we
  infer the progenitors of WD0837+218 and WD0837+185 had masses of 2.6
  &lt;=M&lt;=M<SUB>crit</SUB>M<SUB>solar</SUB> and 2.4 &lt;=M&lt;=
  3.5M<SUB>solar</SUB>, respectively, where M<SUB>crit</SUB> is the
  maximum mass of a white dwarf progenitor. We briefly discuss these
  findings in the context of the observed deficit of white dwarfs in
  open clusters and the initial mass-final mass relationship.

Title: NLTE Analysis of Chandra and XMM-Newton Spectroscopy of CAL 83
Authors: Lanz, T.; Telis, G. A.; Audard, M.; Paerels, F.; Hubeny, I.
Bibcode: 2004HEAD....8.1703L
Altcode: 2004BAAS...36..936L
  We present a new NLTE model atmosphere analysis of Chandra HRC-S/LETG
  and XMM-Newton RGS spectroscopy of the supersoft source CAL 83 in
  the LMC. The two spectra are very similar, and reveal a very rich
  absorption line spectrum from the hot white dwarf photosphere. We also
  report a third X-ray off-state during a later Chandra observation,
  showing the recurrent nature of CAL 83. Moreover, we found evidence
  of short-timescale variability in the soft X-ray spectrum. The Chandra
  and XMM-Newton spectra have been successfully matched with our new NLTE
  line-blanketed model atmospheres that explicitly include 74 ions of the
  11 most abundant species. We derived the basic stellar parameters of the
  hot white dwarf, obtaining the first direct spectroscopic evidence that
  the white dwarf is massive. The short timescale of the X-ray off-states
  is consistent with a high WD mass. Our analysis, therefore, provides
  direct support for supersoft sources as likely progenitors of SN Ia. <P
  />This work was supported by a grant from the NASA Astrophysics Theory
  Program. The Columbia group acknowledges support from NASA to Columbia
  University for XMM-Newton mission support and data analysis

Title: Relativistic, non-LTE Accretion Disk Models of High State
    Black Hole X-ray Binaries
Authors: Davis, S. W.; Blaes, O. M.; Hubeny, I.
Bibcode: 2004HEAD....8.1503D
Altcode: 2004BAAS...36..926D
  We present the first self-consistent calculations of non-LTE,
  relativistic accretion disk models applicable to the high/soft state
  of black hole X-ray binaries. We include the effects of thermal
  Comptonization and bound-free and free-free opacities of abundant ion
  species. Taking into account the relativistic propagation of photons
  from the local disk surface to an observer at infinity, we present
  spectra calculated for a variety of accretion rates, black hole spin
  parameters, disk inclinations, and assumptions of the microphysics of
  the disk. The last include a variety of viscosity prescriptions and
  vertical dissipation profiles, including those recently derived from
  radiation MHD simulations of magnetorotational turbulence. <P />The
  computed spectra are remarkably robust and independent of many of the
  microphysical assumptions. However, the improvement in the physics
  results in discrepancies with previous, more simplified models,
  that are easily discernible with modern X-ray observatories. Fitting
  our spectra with simple, isotropic color-corrected multi-temperature
  blackbodies results in frequency dependent, 10 percent discrepancies
  that may affect the fitted parameters of other spectral components,
  and their interpretation. We compare our models to existing spectral
  data of the high/soft state, and recover the observed relation between
  luminosity and inner disk temperature. <P />We provide an XSPEC table
  model of our spectral calculations for use by the community. <P />This
  work was supported by NASA grant NAG5-13228.

Title: X-ray Heated Accretion Discs around Stellar Mass Black Holes
Authors: Hubeny, I.; Wickramasinghe, D. T.
Bibcode: 2004RMxAC..20..200H
Altcode: 2004IAUCo.194..200H
  We investigate the effects of irradiation on the vertical structure
  of accretion discs around black holes and its impact on the emergent
  energy distribution. Models are presented for a 10 Solar mass black
  hole in a low mass X-ray binary assuming a black body spectrum for
  the incident radiation. We show that for a disc annulus at a given
  radius, the spectra become increasingly distorted as the incident flux
  increases relative to the viscously generated heating flux in the
  disc. Significant effects are apparent for rings even at distances
  of ~ 10,000 Schwarzschild radii from the black hole for realistic
  dilution factors.

Title: Theoretical Radii of Transiting Giant Planets: The Case
    of OGLE-TR-56b
Authors: Burrows, A.; Hubeny, I.; Hubbard, W. B.; Sudarsky, D.;
   Fortney, J. J.
Bibcode: 2004ApJ...610L..53B
Altcode: 2004astro.ph..5264B
  We calculate radius versus age trajectories for the photometrically
  selected transiting extrasolar giant planet, OGLE-TR-56b, and find
  agreement between theory and observation, without introducing an ad hoc
  extra source of heat in its core. The fact that the radius of HD 209458b
  seems larger than the radii of the recently discovered OGLE family
  of extremely close-in transiting planets suggests that HD 209458b is
  anomalous. Nevertheless, our good fit to OGLE-TR-56b bolsters the notion
  that the generic dependence of transit radii on stellar irradiation,
  mass, and age is, to within error bars, now quantitatively understood.

Title: Spectra and Diagnostics for the Direct Detection of
    Wide-Separation Extrasolar Giant Planets
Authors: Burrows, Adam; Sudarsky, David; Hubeny, Ivan
Bibcode: 2004ApJ...609..407B
Altcode: 2004astro.ph..1522B
  We calculate as a function of orbital distance, mass, and age the
  theoretical spectra and orbit-averaged planet/star flux ratios for
  representative wide-separation extrasolar giant planets (EGPs) in
  the optical, near-infrared, and mid-infrared. Stellar irradiation of
  the planet's atmosphere and the effects of water and ammonia clouds
  are incorporated and handled in a consistent fashion. We include
  predictions for 12 specific known EGPs. In the process, we derive
  physical diagnostics that can inform the direct EGP detection and
  remote sensing programs now being planned or proposed. Furthermore, we
  calculate the effects of irradiation on the spectra of a representative
  companion brown dwarf as a function of orbital distance.

Title: Evidence for Flash Mixing in He-rich sdB Stars
Authors: Sweigart, Allen V.; Lanz, Thierry; Brown, Thomas M.; Hubeny,
   Ivan; Landsman, Wayne B.
Bibcode: 2004Ap&SS.291..367S
Altcode: 2003astro.ph..8517S
  We present FUSE spectra of three He-rich sdB stars. Two of these stars,
  PG1544+488 and JL87, reveal extremely strong C III lines, suggesting
  that they have mixed triple-α carbon from the deep interior out to
  their surfaces. Using TLUSTY NLTE line-blanketed model atmospheres, we
  find that PG1544+488 has a surface composition of 96% He, 2% C, and 1%
  N. JL87 shows a similar surface enrichment of C and N but still retains
  a significant amount of hydrogen. In contrast, the third star, LB1766,
  is devoid of hydrogen and strongly depleted of carbon, indicating that
  its surface material has undergone CN-cycle processing.

Title: Thoughts on the Theory of Irradiated Giant Planets
Authors: Burrows, Adam; Sudarsky, David; Hubeny, Ivan
Bibcode: 2004AIPC..713..143B
Altcode:
  We have derived physical diagnostics that can inform the direct
  detection and remote sensing programs of extrasolar giant planets
  (EGPs) now being planned or proposed. Stellar irradiation of the
  planet's atmosphere and the effects of water and ammonia clouds are
  incorporated in a consistent fashion. Whether an EGP is at wide or
  close-in separations from its parent star, direct detection will soon
  be possible and will yield centrally important physical and chemical
  constraints. Our theory of irradiated EGPs is being developed to meet
  this challenge.

Title: AGN SEDs and the Big Blue Bump
Authors: Shang, Z.; Brotherton, M.; Green, R.; Kriss, G.; Scott, J.;
   Kim, J.; Blaes, O.; Hubeny, I.; Zheng, W.; Kaiser, M.; Oegerle, W.;
   Hutchings, J.
Bibcode: 2004AAS...204.9206S
Altcode: 2004BAAS...36Q.824S
  We have constructed SEDs of 17 AGNs with quasi-simultaneous
  spectrophotometry from 900-9000Å (rest frame), using FUSE, HST and
  KPNO. Taking advantage of the short-wavelength coverage, we are able
  to study the big blue bump in detail. A wavelength break around
  1000Å is seen for most objects, but we do not see a correlation
  between the far ultraviolet spectral index and the black hole mass,
  as expected by some accretion disk models. We have also compared our
  sample with the disk models of different black hole mass, Eddington
  ratio, and disk inclination etc., and argue that intrinsic reddening
  as well as Comptonization can strongly bias the observed FUV spectral
  index. <P />This work is based on data obtained for the Guaranteed Time
  Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins
  University. Financial support to U. S. participants has been provided
  by NASA contract NAS5-32985 and NAS5-26555.

Title: The Hot White Dwarf in the Cataclysmic Variable MV Lyrae
Authors: Hoard, D. W.; Linnell, A. P.; Szkody, Paula; Fried, Robert
   E.; Sion, Edward M.; Hubeny, Ivan; Wolfe, M. A.
Bibcode: 2004ApJ...604..346H
Altcode:
  We have obtained the first far-ultraviolet spectrum of the nova-like
  cataclysmic variable MV Lyrae using the Far Ultraviolet Spectroscopic
  Explorer (FUSE). We also obtained contemporaneous optical light
  curves and spectra. All data are from a deep faint accretion state
  of MV Lyr. We constructed a model for the system using the BINSYN
  software package; results from this model include the following: (1)
  The white dwarf has T<SUB>eff</SUB>=47,000K, photospheric logg=8.25,
  and metallicity of Z~0.3Z<SUB>solar</SUB>. (2) The secondary star is
  cooler than 3500 K; it contributes nothing to the far-ultraviolet
  flux and a varying amount to the optical flux (from 10% at 5200
  Å to 60% at 7800 Å). (3) The accretion disk, if present at all,
  contributes negligibly to the spectrum of MV Lyr. Irradiation
  considerations imply that the mass transfer rate is no more than
  3×10<SUP>-13</SUP>M<SUB>solar</SUB>yr<SUP>-1</SUP>. (4) Assuming
  no disk is present, the model optical light curve has an amplitude
  approximately 50% larger than that of the sinusoidal modulation (on
  the orbital period) in the observed optical light curve, suggesting
  that the secondary star might be shaded by a nascent disk and/or have
  starspots near the L1 point. (5) The scaling of the model spectrum to
  the observed data leads to a distance of d=505+/-50pc to MV Lyr. <P
  />This research is based on observations with the NASA-CNES-CSA Far
  Ultraviolet Spectroscopic Explorer, which is operated for NASA by
  the Johns Hopkins University under NASA contract NAS5-32985, and on
  observations obtained with the Apache Point Observatory 3.5 m telescope,
  which is owned and operated by the Astrophysical Research Consortium.

Title: Far Ultraviolet Spectroscopic Explorer Observations of G226-29:
    First Detection of the H<SUB>2</SUB> Quasi-molecular Satellite at
    1150 Å
Authors: Allard, N. F.; Hébrard, G.; Dupuis, J.; Chayer, P.; Kruk,
   J. W.; Kielkopf, J.; Hubeny, I.
Bibcode: 2004ApJ...601L.183A
Altcode: 2003astro.ph.12494A
  We present new far-ultraviolet observations of the pulsating DA white
  dwarf G226-29 obtained with the Far Ultraviolet Spectroscopic Explorer
  (FUSE). This ZZ Ceti star is the brightest one of its class and the
  coolest white dwarf observed by FUSE. We report the first detection of
  the broad quasi-molecular collision-induced satellite of Lyβ at 1150
  Å, an absorption feature that is due to transitions that take place
  during close collisions of hydrogen atoms. The physical interpretation
  of this feature is based on recent progress of the line-broadening
  theory of the far wing of Lyβ. This predicted feature had never been
  observed before, even in laboratory spectra.

Title: Flash Mixing on the White Dwarf Cooling Curve: Far Ultraviolet
    Spectroscopic Explorer Observations of Three He-rich sdB Stars
Authors: Lanz, Thierry; Brown, Thomas M.; Sweigart, Allen V.; Hubeny,
   Ivan; Landsman, Wayne B.
Bibcode: 2004ApJ...602..342L
Altcode: 2003astro.ph..8440L
  We present Far-Ultraviolet Spectroscopic Explorer (FUSE) spectra of
  three He-rich sdB stars. Two of these stars, PG 1544+488 and JL 87,
  reveal extremely strong C III lines at 977 and 1176 Å, while the
  carbon lines are quite weak in the third star, LB 1766. We have
  analyzed the FUSE data using TLUSTY non-LTE line-blanketed model
  atmospheres and find that PG 1544+488 has a surface composition of
  96% He, 2% C, and 1% N. JL 87 shows a similar surface enrichment of
  carbon and nitrogen, but some significant fraction of hydrogen still
  remains in its atmosphere. Finally, LB 1766 has a surface composition
  devoid of hydrogen and strongly depleted of carbon, indicating that
  its surface material has undergone CN-cycle processing. We interpret
  these observations with new evolutionary calculations which suggest
  that He-rich sdB stars with C-rich compositions are the progeny of
  stars which underwent a delayed helium-core flash on the white-dwarf
  cooling curve. During such a flash the interior convection zone will
  penetrate into the hydrogen envelope, thereby mixing the envelope
  with the He- and C-rich core. Such ``flash-mixed'' stars will arrive
  on the extreme horizontal branch (EHB) with He- and C-rich surface
  compositions and will be hotter than the hottest canonical (i.e.,
  unmixed) EHB stars. Two types of flash mixing are possible: ``deep'' and
  ``shallow,'' depending on whether the hydrogen envelope is mixed deeply
  into the site of the helium flash or only with the outer layers of the
  core. Based on both their stellar parameters and surface compositions,
  we suggest that PG 1544+488 and JL 87 are examples of ``deep'' and
  ``shallow'' flash mixing, respectively. Flash mixing may therefore
  represent a new evolutionary channel for producing the hottest EHB
  stars. However, flash mixing cannot explain the abundance pattern in
  LB 1766, which remains a challenge to current evolutionary models. <P
  />Based on observations made with the NASA-CNES-CSA Far Ultraviolet
  Spectroscopic Explorer. FUSE is operated for NASA by the Johns Hopkins
  University under NASA contract NAS5-32985.

Title: Quantitative Spectroscopy of O Stars at Low Metallicity:
    O Dwarfs in NGC 346
Authors: Bouret, J. -C.; Lanz, T.; Hillier, D. J.; Heap, S. R.;
   Hubeny, I.; Lennon, D. J.; Smith, L. J.; Evans, C. J.
Bibcode: 2003ApJ...595.1182B
Altcode: 2003astro.ph..1454B
  We present the results of a detailed analysis of the properties of dwarf
  O-type stars in a metal-poor environment. High-resolution, high-quality
  ultraviolet and optical spectra of six O-type stars in the H II region
  NGC 346 have been obtained from a spectroscopic survey of O stars in the
  SMC. Stellar parameters and chemical abundances have been determined
  using non-LTE (NLTE) line-blanketed photospheric models calculated
  with TLUSTY. Additionally, we have modeled the spectra with the NLTE
  line-blanketed wind code CMFGEN to derive wind parameters. Stellar
  parameters, chemical abundances, and in particular iron abundances
  obtained with the two NLTE codes compare quite favorably. This
  consistency demonstrates that basic photospheric parameters of
  main-sequence O stars can be reliably determined using NLTE static
  model atmospheres. With the two NLTE codes, we need to introduce a
  microturbulent velocity to match the observed spectra. Our results
  hint at a decrease of the required microturbulent velocity from a value
  close to the sonic velocity in early O stars to a low value in late O
  stars. As in several recent studies of Galactic, LMC, and SMC stars, we
  derive effective temperatures lower than predicted from the widely used
  relation between spectral type and T<SUB>eff</SUB>, resulting in lower
  stellar luminosities and lower ionizing fluxes. From evolutionary tracks
  in the H-R diagram, we find the age 3×10<SUP>6</SUP> yr for NGC 346. A
  majority of the stars in our sample reveal CNO cycle-processed material
  at their surface during the main-sequence stage, thus indicating fast
  stellar rotation and/or very efficient mixing processes. We obtain an
  overall metallicity Z=0.2Z<SUB>solar</SUB>, in good agreement with other
  recent analyses of SMC stars. We study the dependence of the mass-loss
  rate on the stellar metallicity and find a satisfactory agreement with
  recent theoretical predictions for the three most luminous stars of
  the sample. The wind momentum-luminosity relation for our sample stars
  derived for these stars agrees with previous studies. However, the three
  other stars of our sample reveal very weak signatures of mass loss. We
  obtain mass-loss rates that are significantly lower than 10<SUP>-8</SUP>
  M<SUB>solar</SUB> yr<SUP>-1</SUP>, below the predictions of radiative
  line-driven wind theory by an order of magnitude or more. Furthermore,
  evidence of clumping in the wind of main-sequence O stars is provided
  by O V λ1371. As in previous studies of O star winds, we are unable to
  reproduce this line with homogeneous-wind models, but we have achieved
  very good fits with clumped models. Clumped-wind models systematically
  yield lower mass-loss rates than theoretical predictions. <P />Based
  on observations with the NASA/ESA Hubble Space Telescope, obtained
  at the Space Telescope Science Institute, which is operated by the
  Association of Universities for Research in Astronomy, Inc., under
  NASA contract NAS 5-2655. Also based on observations obtained at the
  European Southern Observatory (La Silla) and at the Anglo-Australian
  Observatory (Siding Spring).

Title: Search for forced oscillations in binaries.  IV. The eclipsing
    binary V436 Per revisited
Authors: Janík, J.; Harmanec, P.; Lehmann, H.; Yang, S.; Božić,
   H.; Ak, H.; Hadrava, P.; Eenens, P.; Ruždjak, D.; Sudar, D.; Hubeny,
   I.; Linnell, A. P.
Bibcode: 2003A&A...408..611J
Altcode:
  An analysis of new spectroscopic and photoelectric U B V observations,
  satisfactorily covering the whole orbital period of V436 Per, together
  with existing data allowed us to improve the knowledge of the basic
  physical characteristics of the binary and its components. In several
  aspects, our new results differ from the findings of Paper I of this
  series: in particular, we found that it is the star eclipsed in the
  secondary minimum which is slightly more massive and larger than
  the optical primary. We also conclude that the apsidal advance -
  if present at all - is much slower than that estimated in a previous
  study. The orbital period might be increasing by 0.28 s per year but
  also this finding is very uncertain and needs verification by future
  observations. It is encouraging to note that two completely independent
  sets of programs for light-curve solutions lead to identical results. A
  notable finding is that both binary components rotate with very
  similar - if not identical - rotational periods of 1<SUP>d</SUP>.45
  and 1<SUP>d</SUP>.40, much shorter than what would correspond to a
  10<SUP>d</SUP>.9 spin-orbit synchronization period at periastron. Rapid
  line-profile changes reported earlier could not be confirmed from new,
  dedicated series of high-resolution and S/N spectra. <P />This research
  is based on spectra from the Dominion Astrophysical Observatory (DAO),
  Ondřejov, and Thuringer Landessternwarte (TLS) Tautenburg.

Title: VizieR Online Data Catalog: V436 Persei UBV photometry
    (Janik+, 2003)
Authors: Janik, J.; Harmanec, P.; Lehmann, H.; Yang, S.; Bozic, H.;
   Ak, H.; Hadrava, P.; Eenens, P.; Ruzdjak, D.; Sudar, D.; Hubeny, I.;
   Linnell, A. P.
Bibcode: 2003yCat..34080611J
Altcode:
  An analysis of new spectroscopic and photoelectric UBV observations,
  satisfactorily covering the whole orbital period of V436 Per, together
  with existing data allowed us to improve the knowledge of the basic
  physical characteristics of the binary and its components. In several
  aspects, our new results differ from the findings of Paper I (Harmanec
  et al., 1997, Cat. &lt;J/A+A/319/867&gt;) of this series: In particular,
  we found that it is the star eclipsed in the secondary minimum which
  is slightly more massive and larger than the optical primary. We also
  conclude that the apsidal advance -- if present at all -- is much
  slower than that estimated in a previous study. The orbital period
  might be increasing by 0.28 s per year but also this finding is
  very uncertain and needs verification by future observations. It is
  encouraging to note that two completely independent sets of programs
  for light-curve solutions lead to identical results. A notable finding
  is that both binary components rotate with very similar -- if not
  identical -- rotational periods of 1.45d and 1.40d, much shorter than
  what would correspond to a 10.9d spin-orbit synchronization period
  at periastron. Rapid line-profile changes reported earlier could not
  be confirmed from new, dedicated series of high-resolution and S/N
  spectra. <P />(2 data files).

Title: Anomalous Ultraviolet Line Flux Ratios in the Cataclysmic
    Variables 1RXS J232953.9+062814, CE 315, BZ Ursae Majoris, and EY
    Cygni, Observed with the Hubble Space Telescope Space Telescope
    Imaging Spectrograph
Authors: Gänsicke, Boris T.; Szkody, Paula; de Martino, Domitilla;
   Beuermann, Klaus; Long, Knox S.; Sion, Edward M.; Knigge, Christian;
   Marsh, Tom; Hubeny, Ivan
Bibcode: 2003ApJ...594..443G
Altcode: 2003astro.ph..5264G
  Brief Hubble Space Telescope Space Telescope Imaging Spectrograph
  spectroscopic snapshot exposures of the cataclysmic variables 1RXS
  J232953.9+062814, CE 315, BZ UMa, and EY Cyg reveal very large N
  V/C IV line flux ratios, similar to those observed in AE Aqr. Such
  anomalous line flux ratios have so far been observed in 10 systems and
  presumably reflect a different composition of the accreted material
  compared to the majority of cataclysmic variables. We discuss the
  properties of this small sample in the context of the recent proposal
  by Schenker et al. that a significant fraction of the present-day
  population of cataclysmic variables may have passed through a phase of
  thermal timescale mass transfer. <P />Based on observations made with
  the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope
  Science Institute, which is operated by the Association of Universities
  for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Title: A comparison of DA white dwarf temperatures and gravities
    from FUSE Lyman line and ground-based Balmer line observations
Authors: Barstow, M. A.; Good, S. A.; Burleigh, M. R.; Hubeny, I.;
   Holberg, J. B.; Levan, A. J.
Bibcode: 2003MNRAS.344..562B
Altcode: 2003astro.ph..6077B
  The observation of the strengths and profiles of the hydrogen
  Balmer absorption series is an established technique for determining
  the effective temperature and surface gravity of hot H-rich white
  dwarf stars. In principle, the Lyman series lines should be equally
  useful but, lying in the far-ultraviolet (FUV), are only accessible
  from space. Nevertheless, there are situations (for example, where
  the optical white dwarf spectrum is highly contaminated by the
  presence of a companion) in which use of the Lyman series may be
  essential. Therefore, it is important to establish whether or not the
  Lyman lines provide an equally valid means of measurement. We have
  already made a first attempt to study this problem, comparing Lyman
  line measurements from a variety of FUV instruments with ground-based
  Balmer line studies. Within the measurement uncertainties, we found
  the results from each line series to be broadly in agreement. However,
  we noted a number of potential systematic effects that could bias
  either measurement. With the availability of the Far Ultraviolet
  Spectroscopic Explorer (FUSE) data archive and observations from our
  own Guest Observer programmes, we now have an opportunity to examine
  the use of the Lyman series in more detail from observations of 16
  DA white dwarfs. Here we have data produced by a single instrument
  and processed with a uniform data reduction pipeline, eliminating
  some of the possible systematic differences between observations of
  the same or different stars. We have also examined the scatter in
  values derived from multiple observations of the same star, which is
  significant. The new results partially reproduce the earlier study,
  showing that Balmer and Lyman line determined temperatures are in
  good agreement up to ~50 000 K. However, above this value there is an
  increasing systematic difference between the Lyman and Balmer line
  results, the former yielding the higher temperature. At the moment,
  there is no clear explanation of this effect but we think that it
  is most likely associated with deficiencies in the detailed physics
  incorporated into the stellar model atmosphere calculations. Even so,
  the data do demonstrate that, for temperatures below 50 000 K, the
  Lyman lines give reliable results. Furthermore, for the hotter stars,
  a useful empirical calibration of the relationship between the Lyman
  and Balmer measurements has been obtained, which can be applied to
  other FUSE observations.

Title: A Possible Bifurcation in Atmospheres of Strongly Irradiated
    Stars and Planets
Authors: Hubeny, Ivan; Burrows, Adam; Sudarsky, David
Bibcode: 2003ApJ...594.1011H
Altcode: 2003astro.ph..5349H
  We show that under certain circumstances the differences between
  the absorption mean and Planck mean opacities can lead to multiple
  solutions for an LTE atmospheric structure. Since the absorption and
  Planck mean opacities are not expected to differ significantly in the
  usual case of radiative equilibrium, nonirradiated atmospheres, the
  most interesting situations in which the effect may play a role are
  strongly irradiated stars and planets, and also possibly structures
  in which there is a significant deposition of mechanical energy, such
  as stellar chromospheres and accretion disks. We have presented an
  illustrative example of a strongly irradiated giant planet in which
  the bifurcation effect is predicted to occur for a certain range of
  distances from the star.

Title: Non-LTE Model Atmospheres for Late-Type Stars. I. A Collection
    of Data for Light Neutral and Singly Ionized Atoms
Authors: Allende Prieto, Carlos; Lambert, David L.; Hubeny, Ivan;
   Lanz, Thierry
Bibcode: 2003ApJS..147..363A
Altcode: 2003astro.ph..3559A; 2003astro.ph..3559P
  With the goal of producing a reliable set of model atoms and singly
  ionized ions for use in building NLTE model atmospheres, we have
  combined measured energy levels, critically compiled line transition
  probabilities, and resonance-averaged calculations of photoionization
  cross sections. <P />A majority of the elements from Li to Ca are
  considered, covering most of the important species in late-type
  atmospheres. These include elements that contribute free electrons
  and/or continuous opacity in the ultraviolet (e.g., Mg and Si), as well
  as trace elements whose abundance determinations rely on ultraviolet
  lines (e.g., B from B I lines). The new data complement and, for the
  species in common, supersede a previous collection of model atoms
  originally designed for use in studies of early-type stars.

Title: Erratum: ``A Grid of Non-LTE Line-blanketed Model Atmospheres
    of O-Type Stars'' (<A href="bib_query?2003ApJS...146..417L">ApJS,
    146, 417 [2003]</A>)
Authors: Lanz, Thierry; Hubeny, Ivan
Bibcode: 2003ApJS..147..225L
Altcode:
  We have constructed a comprehensive grid of 680 metal line-blanketed,
  non-LTE, plane-parallel, hydrostatic model atmospheres for the basic
  parameters appropriate to O-type stars. The OSTAR2002 grid considers 12
  values of effective temperatures, 27,500K&lt;=T<SUB>eff</SUB>&lt;=55,000
  K with 2500 K steps, eight surface gravities, 3.0&lt;=logg&lt;=4.75
  with 0.25 dex steps, and 10 chemical compositions, from metal-rich
  relative to the Sun to metal-free. The lower limit of logg for a
  given effective temperature is set by an approximate location of the
  Eddington limit. The selected chemical compositions have been chosen
  to cover a number of typical environments of massive stars: the
  Galactic center, the Magellanic Clouds, blue compact dwarf galaxies
  like I Zw 18, and galaxies at high redshifts. The paper contains a
  description of the OSTAR2002 grid and some illustrative examples and
  comparisons. The complete OSTAR2002 grid is available at our Web site
  at <A href="/abs/2003ApJ..S.146..417L">ApJS, 146, 417 [2003]</A>. <P
  />Laboratory for Astronomy and Solar Physics, NASA Goddard Space Flight
  Center, Code 681, Greenbelt, MD 20771.

Title: Modeling of the Lyman gamma  satellites in FUSE spectra of
    DA white dwarfs
Authors: Hébrard, G.; Allard, N. F.; Kielkopf, J. F.; Chayer, P.;
   Dupuis, J.; Kruk, J. W.; Hubeny, I.
Bibcode: 2003A&A...405.1153H
Altcode: 2003astro.ph..5356H
  We present new theoretical calculations of the line profile of Lyman
  gamma that include transitions in which a photon is absorbed by a
  neutral hydrogen atom while it interacts with a proton. Models show
  that two absorption features located near 992 Å and 996 Å are due
  to H-H<SUP>+</SUP> collisions. These quasi-molecular satellites are
  similar to those that were identified in the wings of Lyman alpha and
  Lyman beta lines of hydrogen-rich white dwarfs. We compute synthetic
  spectra that take account of these new theoretical profiles and compare
  them to the spectra of four DA white dwarfs that were observed with
  FUSE. The models predict the absorption features that are observed in
  the wing of Lyman gamma near 995 Å, and confirm that these features
  are quasi-molecular satellites. <P />This paper is dedicated in memory
  of J. L. Greenstein, discoverer of the quasi-molecular lines in white
  dwarfs, who passed away on October 21, 2002.

Title: Non-LTE Model Atmospheres for Late-Type Stars. II. Restricted
    Non-LTE Calculations for a Solar-like Atmosphere
Authors: Allende Prieto, Carlos; Hubeny, Ivan; Lambert, David L.
Bibcode: 2003ApJ...591.1192A
Altcode: 2003astro.ph..3560A; 2003astro.ph..3560P
  We test our knowledge of the atomic opacity in the solar UV
  spectrum. Using the atomic data compiled in the first paper in
  this series from modern, publicly available databases, we perform
  calculations that are compared with space-based observations of
  the Sun. At wavelengths longer than about 2600 Å, LTE modeling can
  reproduce quite closely the observed fluxes; uncertainties in the atomic
  line data account fully for the differences between calculated and
  observed fluxes. At shorter wavelengths, departures from LTE appear
  to be important, since our LTE and restricted non-LTE calculations
  differ. Analysis of visible/near-IR Na I and O I lines, two species
  that produce a negligible absorption in the UV, shows that observed
  departures from LTE for these species can be reproduced very accurately
  with restricted (fixed atmospheric structure) non-LTE calculations.

Title: A Grid of Non-LTE Line-blanketed Model Atmospheres of O-Type
    Stars
Authors: Lanz, Thierry; Hubeny, Ivan
Bibcode: 2003ApJS..146..417L
Altcode: 2002astro.ph.10157L
  We have constructed a comprehensive grid of 680 metal line-blanketed,
  non-LTE, plane-parallel, hydrostatic model atmospheres for the basic
  parameters appropriate to O-type stars. The OSTAR2002 grid considers 12
  values of effective temperatures, 27,500K&lt;=T<SUB>eff</SUB>&lt;=55,000
  K with 2500 K steps, eight surface gravities, 3.0&lt;=logg&lt;=4.75
  with 0.25 dex steps, and 10 chemical compositions, from metal-rich
  relative to the Sun to metal-free. The lower limit of logg for a given
  effective temperature is set by an approximate location of the Eddington
  limit. The selected chemical compositions have been chosen to cover a
  number of typical environments of massive stars: the Galactic center,
  the Magellanic Clouds, blue compact dwarf galaxies like I Zw 18, and
  galaxies at high redshifts. The paper contains a description of the
  OSTAR2002 grid and some illustrative examples and comparisons. The
  complete OSTAR2002 grid is available on-line.

Title: Theoretical Spectra and Atmospheres of Extrasolar Giant Planets
Authors: Sudarsky, David; Burrows, Adam; Hubeny, Ivan
Bibcode: 2003ApJ...588.1121S
Altcode: 2002astro.ph.10216S
  We present a comprehensive theory of the spectra and atmospheres of
  irradiated extrasolar giant planets. We explore the dependences on
  stellar type, orbital distance, cloud characteristics, planet mass, and
  surface gravity. Phase-averaged spectra for specific known extrasolar
  giant planets that span a wide range of the relevant parameters are
  calculated, plotted, and discussed. The connection between atmospheric
  composition and emergent spectrum is explored in detail. Furthermore, we
  calculate the effect of stellar insolation on brown dwarfs. We review
  a variety of representative observational techniques and programs
  for their potential for direct detection, in light of our theoretical
  expectations, and we calculate planet-to-star flux ratios as a function
  of wavelength. Our results suggest which spectral features are most
  diagnostic of giant planet atmospheres and reveal the best bands in
  which to image planets of whatever physical and orbital characteristics.

Title: Heavy-element abundance patterns in hot DA white dwarfs
Authors: Barstow, M. A.; Good, S. A.; Holberg, J. B.; Hubeny, I.;
   Bannister, N. P.; Bruhweiler, F. C.; Burleigh, M. R.; Napiwotzki, R.
Bibcode: 2003MNRAS.341..870B
Altcode: 2003astro.ph..1519B
  We present a series of systematic abundance measurements for 25 hot
  DA white dwarfs in the temperature range ~20 000-110 000 K, based
  on far-ultraviolet spectroscopy with the Space Telescope Imaging
  Spectrograph (STIS)/Goddard High Resolution Spectrograph (GHRS)
  on-board Hubble Space Telescope, IUE and FUSE. Using our latest
  heavy-element blanketed non-local thermodynamic equilibrium (non-LTE)
  stellar atmosphere calculations we have addressed the heavy-element
  abundance patterns, making completely objective measurements of
  abundance values and upper limits using a χ<SUP>2</SUP> fitting
  technique to determine the uncertainties in the abundance measurements,
  which can be related to the formal upper limits in those stars
  where particular elements are not detected. <P />We find that the
  presence or absence of heavy elements in the hot DA white dwarfs
  largely reflects what would be expected if radiative levitation is
  the supporting mechanism, although the measured abundances do not
  match the predicted values very well, as reported by other authors
  in the past. Almost all stars hotter than ~50 000 K contain heavy
  elements. For most of these the spread in element abundances is quite
  narrow and similar to the abundances measured in G191-B2B. However,
  there is an unexplained dichotomy at lower temperatures with some
  stars having apparently pure H envelopes and others having detectable
  quantities of heavy elements. The heavy elements present in these
  cooler stars are often stratified, lying in the outermost layers of
  the envelope. A few strong temperature/evolutionary effects are seen
  in the abundance measurements. There is a decreasing Si abundance with
  temperature, the N abundance pattern splits into two groups at lower
  temperature and there is a sharp decline in Fe and Ni abundance to zero,
  below ~50 000 K. When detected, the Fe and Ni abundances maintain an
  approximately constant ratio, close to the cosmic value of ~20. For
  the hottest white dwarfs observed by STIS, the strongest determinant
  of abundance appears to be gravity.

Title: A Tale of Two Stars: The Extreme O7 Iaf+ Supergiant AV 83
    and the OC7.5 III((f)) star AV 69
Authors: Hillier, D. John; Lanz, T.; Heap, S. R.; Hubeny, I.; Smith,
   L. J.; Evans, C. J.; Lennon, D. J.; Bouret, J. C.
Bibcode: 2003ApJ...588.1039H
Altcode:
  We present a detailed study of AV 83, an O7 Iaf+ supergiant,
  and AV 69 [OC7.5 III((f))] in the SMC. The stars have similar
  effective temperatures and luminosities but show very different wind
  signatures. For our study we have used the non-LTE line-blanketed
  atmosphere code developed by Hillier and Miller, which explicitly
  allows for line blanketing by C, N, O, S, Ar, Ne, Fe, and other
  elements. Our study finds that AV 83 has an effective temperature of
  approximately 33,000 K and logg~3.25. It has an extended photosphere
  as a result of a ``low'' effective surface gravity and a much denser
  wind than main-sequence O stars. We can match the spectrum only by
  using a slow velocity law with β~2, a value that is much larger
  than the values of around 1 predicted by standard radiation wind
  theory. Further, we show that the Hα emission profile in AV 83 is
  sensitive to the adopted surface gravity. To fit the spectrum of AV 83,
  we have considered conventional models in which the wind is smooth
  and alternate models in which the winds are highly clumped. Both
  types of winds yield a satisfactory fit to the majority of lines
  in the observed spectrum; however, strong UV photospheric lines
  and the P V resonance transitions favor a clumped wind. If clumping
  is important, it must begin at relatively low velocities (i.e., 30
  km s<SUP>-1</SUP>, not 300 km s<SUP>-1</SUP>). In the smooth wind,
  the line force is too small to drive the wind. In the clumped wind,
  the line force is generally sufficient to drive the wind, although
  there are still some discrepancies around the sonic point. In AV
  83, the N abundance is substantially enhanced relative to normal
  SMC abundances, while both C and O are SMC-like, consistent with
  the presence of internally processed CNO material at the stellar
  surface. The N III λ4640 multiplet, which is known to be produced by
  dielectronic recombination, is well reproduced by the models. These
  lines, and the adjacent C III λ4649 multiplet, show a significant
  sensitivity to surface gravity, as well as the usual sensitivity to
  abundance and effective temperature. Incoherent electron scattering,
  occurring within the photosphere, can explain the broad wings seen
  on these lines. We have modeled the Fe spectrum (Fe IV-Fe VI) in the
  UV in both AV 83 and AV 69. For stars with an effective temperature
  around 33,000 K, the Fe IV-to-Fe V line ratios form a useful effective
  temperature diagnostic and give results consistent with those found
  from optical and UV line diagnostics. The derived iron abundance, which
  is sensitive to the adopted microturbulent velocity, is 0.2-0.4 times
  the solar iron abundance in AV 83, while 0.2 solar gives a good fit
  for AV 69. The wind of AV 69 is substantially less dense than that of
  AV 83. Because of the lack of suitable diagnostics, it is impossible
  to constrain the mass-loss rate and velocity law independently. Its
  spectrum indicates that it has a similar effective temperature to
  AV 83 (T<SUB>eff</SUB>~34,000 K), a substantially higher gravity
  (logg=3.5) than AV 83, and a CNO abundance pattern that has not been
  influenced by internal CNO processing. We show that the N/C abundance
  ratio is substantially below solar, in agreement with SMC nebular and
  stellar abundance studies. The differences between the spectra of AV
  83 and AV 69, and between the derived masses and surface abundances,
  are striking. We have examined possible causes, and only one seems
  consistent with the observations and our current understanding of
  massive star evolution. AV 83 was most likely a fast rotator that
  experienced rotationally enhanced mass loss. The presence of enhanced
  N but almost normal C and O abundances is a direct indication of
  rotationally induced mixing. On the other hand, AV 69 is a slow
  rotator. As part of our analyses, we have systematically examined
  the influence of the H/He abundance ratio, the mass-loss rate, the
  velocity law, the Fe abundance, microturbulence, and clumping on
  the theoretical spectrum. We illustrate which lines provide useful
  diagnostics and highlight some of the difficulties associated with
  spectroscopic analyses of O stars. The spectrum of AV 83 shows the
  presence of photospheric absorption lines, the presence of lines formed
  at the base of the wind, and numerous wind lines. Since these lines
  sample the photosphere and the entire wind, extreme O If supergiants,
  such as AV 83, are ideal candidates to probe conditions in stellar
  winds and hence further our knowledge of O star winds. <P />Based on
  observations with the NASA/ESA Hubble Space Telescope, obtained at the
  Space Telescope Science Institute, which is operated by the Association
  of Universities for Research in Astronomy, Inc., under NASA contract
  NAS5-26555. Based in part, on observations with the NASA-CNES-CSA Far
  Ultraviolet Spectroscopic Explorer. FUSE is operated by Johns Hopkins
  University under NASA contract NAS5-32985.

Title: On the Indirect Detection of Sodium in the Atmosphere of the
    Planetary Companion to HD 209458
Authors: Fortney, J. J.; Sudarsky, D.; Hubeny, I.; Cooper, C. S.;
   Hubbard, W. B.; Burrows, A.; Lunine, J. I.
Bibcode: 2003ApJ...589..615F
Altcode: 2002astro.ph..8263F
  Using a self-consistent atmosphere code, we construct a new model of
  the atmosphere of the transiting extrasolar giant planet HD 209458b to
  investigate the disparity between the observed strength of the sodium
  absorption feature at 589 nm and the predictions of previous models. For
  the atmospheric temperature-pressure profile we derive, silicate and
  iron clouds reside at a pressure of several millibars in the planet's
  atmosphere. These clouds have significant vertical extent and optical
  depth because of our slant viewing geometry and lead to increased
  absorption in bands directly adjacent to the sodium line core. Using a
  non-LTE sodium ionization model that includes photoionization by stellar
  UV flux, collisional processes with H<SUB>2</SUB>, and radiative
  recombination, we show that the ionization depth in the planet's
  atmosphere reaches ~1/2 mbar at the day/night terminator. Ionization
  leads to a slight weakening of the sodium feature. We present our
  baseline model, including ionization and clouds, which falls near the
  observational error bars. The sensitivity of our conclusions to the
  derived atmospheric temperature-pressure profile is discussed.

Title: An analysis of the optical spectra of the post-asymptotic
    giant branch stars LSIV -12 111 and HD 341617
Authors: Ryans, R. S. I.; Dufton, P. L.; Mooney, C. J.; Rolleston,
   W. R. J.; Keenan, F. P.; Hubeny, I.; Lanz, T.
Bibcode: 2003A&A...401.1119R
Altcode:
  High spectral resolution and signal-to-noise observations of the
  absorption and emission line spectra in two post-asymptotic-giant-branch
  (PAGB) stellar candidates, LSIV -12 111 and HD 314617 are discussed. The
  absorption line spectra have been analysed using non-LTE model
  atmosphere techniques to determine stellar atmospheric parameters
  and chemical compositions, both in absolute terms and relative to
  a standard star, HD 13841. The atmospheric parameters differ from
  previous estimates based on LTE model atmospheres, probably due to
  non-LTE effects. In turn these imply stellar masses that are generally
  larger than have been previously estimated. Both PAGB candidates have
  relative uniform underabundances of metals with mean values of -0.35
  dex for LSIV -12 111 and -0.50 dex for HD 314617. <P />Furthermore,
  their abundance patterns are remarkably similar to that observed
  for optically bright, F-type PAGBs. From the emission spectra, the
  plasma parameters and angular size of the circumstellar material are
  constrained, and these are consistent with previous estimates and with
  a PAGB evolutionary stage.

Title: A New Formation Mechanism for the Hottest Horizontal-Branch
    Stars
Authors: Sweigart, A. V.; Brown, T. M.; Lanz, T.; Landsman, W. B.;
   Hubeny, I.
Bibcode: 2003ASPC..296..313S
Altcode: 2003nhgc.conf..313S; 2002astro.ph..7343S
  Stars with very large mass loss on the red-giant branch can undergo
  the helium flash while descending the white-dwarf cooling curve. Under
  these conditions the flash convection zone will mix the hydrogen
  envelope with the hot helium- burning core. Such ``flash-mixed''
  stars will arrive on the extreme horizontal branch (EHB) with helium-
  and carbon-rich envelopes and will lie at higher temperatures than the
  hottest canonical (i.e., unmixed) EHB stars. Flash mixing provides a
  new evolutionary channel for populating the hot end of the EHB and may
  explain the origin of the high gravity, helium-rich sdO and sdB stars.

Title: Multidimensional ALI Radiative Transfer in Cartesian,
    Cylindrical and Spherical Coordinate Systems
Authors: van Noort, M.; Hubeny, I.; Lanz, T.
Bibcode: 2003ASPC..288..445V
Altcode: 2003sam..conf..445V
  A new Radiative Transfer code that can calculate the non-LTE line
  transfer problem in a two-level atom formulation in Cartesian,
  cylindrical and spherical coordinate systems is presented. The transfer
  equation is solved using the ALI and the short characteristics methods,
  while allowing for an arbitrary 3-dimensional velocity field. <P />The
  code is modularised so that changing geometry can be accomplished by
  simply setting a switch, and parallelised for use on a networked PC
  cluster to increase computational speed. The spatial parallelization
  method is employed. It is found to be robust and efficient, while not
  relying heavily on fast communication. <P />The internal accuracy of
  the code is tested extensively in all three geometries and is shown
  to be in good agreement with appropriate 1-D solutions.

Title: Comparisons between Observed and Computed Visible and Near-UV
    Spectra of Vega
Authors: García-Gil, A.; Allende Prieto, C.; García López, R. J.;
   Hubeny, I.
Bibcode: 2003ASPC..288..145G
Altcode: 2003sam..conf..145G
  By using the Synspec program with different LTE and NLTE atmospheric
  models of Alpha Lyrae (Vega, spectral type A0V), we obtain different
  emitted fluxes. Taking into account the distance from Hipparcos, it
  is obtained the spectrum that would be observed from Earth for each
  model. This spectrum is compared with UV calibrations from the IUE
  and UARS satellites and visible ground-based observations. Absolute
  fluxes from the SOLSTICE experiment onboard UARS provide an independent
  source to assess the quality of the available data. The main goal
  of this work is to better understand and solve the controversy about
  the missing opacity problem in the UV. This is just the first step in
  that direction.

Title: A Detailed View of the Photosphere of the Hot White Dwarf
    G191-B2B from STIS
Authors: Holberg, J. B.; Barstow, M. A.; Hubeny, I.; Sahu, M. S.;
   Bruhweiler, F. C.; Landsman, W. B.
Bibcode: 2003ASPC..291..383H
Altcode: 2003hslf.conf..383H
  No abstract at ADS

Title: Quantitative analysis of O-type stars properties, at low
    metallicity
Authors: Bouret, Jean-Claude; Lanz, Thierry M.; Heap, Sara R.; Hubeny,
   Ivan; Hillier, D. John; Lennon, Daniel J.; Evans, Christopher J.;
   Smith, Linda J.
Bibcode: 2003IAUS..212..156B
Altcode:
  We have investigated the properties of main-sequence O-type stars in
  the SMC. Mass-loss rates, luminosities and T<SUB>eff</SUB> are much
  smaller for these stars than for Galactic ones, resulting in a steeper
  wind-momentum relation.

Title: Accelerated Lambda Iteration: An Overview
Authors: Hubeny, I.
Bibcode: 2003ASPC..288...17H
Altcode: 2003sam..conf...17H
  No abstract at ADS

Title: A Grid of Non-LTE Line-Blanketed Model Atmospheres of O Stars
Authors: Lanz, T.; Hubeny, I.
Bibcode: 2003ASPC..288..157L
Altcode: 2003sam..conf..157L
  We have constructed a grid of over 300 NLTE fully-blanketed model
  atmospheres covering the parameter range of O-type stars at various
  metallicities. We have assumed a plane-parallel geometry, hydrostatic
  and radiative equilibria. The models incorporate about 100,000 NLTE
  atomic levels of over 40 ions of H, He, C, N, O, Ne, Si, P, S, Fe,
  and Ni, which are grouped into about 900 superlevels. The models will
  be made publicly available in the coming months.

Title: Stellar Atmosphere Modeling
Authors: Hubeny, Ivan; Mihalas, Dimitri; Werner, Klaus
Bibcode: 2003ASPC..288.....H
Altcode: 2003sam..conf.....H
  No abstract at ADS

Title: Quantitative Spectroscopy of O stars at low metallicity. O
    Dwarfs in NGC 346
Authors: Bouret, J. -C.; Lanz, T.; Heap, S.; Hubeny, I.; Hillier,
   D.; Lennon, D.; Evans, C. J.; Smith, L.
Bibcode: 2003sf2a.conf..499B
Altcode: 2003sf2a.confE.214B
  Dwarf O-type stars have been observed in NGC 346, the largest HII
  region in the SMC. UV and optical spectra have been analysed with
  NLTE line-blanketed models. These stars reveal CNO- cycle processed
  material at their surface, indicating fast stellar rotation and/or
  very efficient mixing processes. We obtain an overall metallicity
  Z = 0.2 Z<SUB>odot</SUB>. The dependence of the mass loss rate with
  the stellar metallicity is in good agreement with recent theoretical
  predictions for three most luminous stars of the sample. However, three
  other stars reveal mass loss rates that are significantly lower than
  10<SUP>-8</SUP> msol/yr, which is below the predictions of radiative
  line-driven wind theory by an order of magnitude or more. Clumping in
  the wind is evidenced by OV at 1371. Clumped wind models systematically
  yield lower mass loss rates than theoretical predictions.

Title: NLTE Line Formation in Late-Type Stellar Atmospheres
Authors: Allende Prieto, C.; Hubeny, I.; Lambert, D. L.; Lanz, T.
Bibcode: 2003IAUS..210P.A24A
Altcode:
  No abstract at ADS

Title: Quasi-molecular lines in Lyman wings of cool DA white dwarfs;
    Application to FUSE observations of G 231--40
Authors: Allard, N. F.; Hébrard, G.; Ferlet, R.; Vidal-Madjar, A.;
   Hubeny, I.; Lacour, S.
Bibcode: 2003ASIB..105..163A
Altcode: 2003whsw.conf..163A; 2003whdw.conf..163A
  We present new theoretical calculations of Lyman β profiles which
  include perturbations by both neutral hydrogen and protons. They are
  used to improve theoretical modeling of synthetic spectra for cool DA
  white dwarfs.

Title: Model Photospheres with Accelerated Lambda Iteration
Authors: Hubeny, I.; Lanz, T.
Bibcode: 2003ASPC..288...51H
Altcode: 2003sam..conf...51H
  No abstract at ADS

Title: Lyman gamma satellites due to H-H<SUP>+</SUP> collisions:
    Application to FUSE observations of hot white dwarfs
Authors: Allard, N. F.; Bourdreux, S.; Kielkopf, J. F.; Hébrard, G.;
   Désert, J. -M.; Ferlet, R.; Vidal-Madjar, A.; Hubeny, I.; Peek, J. M.
Bibcode: 2003ASIB..105..161A
Altcode: 2003whsw.conf..161A; 2003whdw.conf..161A
  New theoretical calculations of Lyman γ profiles perturbed by protons
  allow us to identificate a large feature near 995Å in FUSE observations
  of hot white dwarfs. This feature is due to quasi-molecular Lyman γ
  satellites due to H-H<SUP>+</SUP> collisions near 991 and 996Å.

Title: Preliminary Analysis of an Extreme Helium sdO Star: BD+25 4655
Authors: Budaj, J.; Elkin, V.; Hubeny, I.
Bibcode: 2003IAUS..210P.E44B
Altcode:
  No abstract at ADS

Title: Atomic Data in Non-LTE Model Stellar Atmospheres
Authors: Lanz, T.; Hubeny, I.
Bibcode: 2003ASPC..288..117L
Altcode: 2003sam..conf..117L
  Extensive sources of atomic data are required to calculate NLTE
  line-blanketed model atmospheres. I will discuss their implementation in
  our NLTE model atmosphere code, TLUSTY, and in our spectrum synthesis
  code, SYNSPEC, with a particular attention to the statistical methods
  required to incorporate the opacity of iron-peak elements. A few
  typical results and comparisons to other codes will be shown.

Title: NLTE Line-Blanketed Model Stellar Atmospheres
Authors: Lanz, T.; Hubeny, I.; Heap, S. R.
Bibcode: 2003IAUS..210...67L
Altcode:
  No abstract at ADS

Title: FUSE Observations of He-rich sdB Stars
Authors: Lanz, T.; Brown, T. M.; Sweigart, A. V.; Hubeny, I.; Landsman,
   W. B.
Bibcode: 2002AAS...20111308L
Altcode: 2002BAAS...34.1285L
  Subdwarf B stars all show significant abundance anomalies. Most are
  extremely deficient in helium and selected light elements, but a
  minority are helium-rich. Deficiencies in helium and heavier elements
  have been attributed to gravitational settling, but the helium-enriched
  members of the class present a puzzling exception, because radiative
  levitation should be too weak to prevent gravitational settling. New
  evolutionary calculations suggest that these helium-rich sdB stars are
  the result of a delayed helium-core flash on the white dwarf cooling
  curve. The convective zone produced by this flash will penetrate
  the hydrogen envelope, mixing hydrogen into the hot helium-burning
  interior, where it is rapidly consumed. The resulting star should show
  greatly enhanced helium and carbon with respect to the other heavy
  elements. This phenomenon is analogous to the born again scenario
  for producing hydrogen-deficient R CrB stars following a very late
  helium-shell flash. We have recently obtained FUSE spectra of two
  helium-rich sdB stars, revealing huge C III lines at 977 and 1176
  Å. Our preliminary analysis yields a surface composition of 97% He
  and 3% C, in agreement with the new evolutionary scenario. This work
  is supported in part by NASA grant NAG5-12383.

Title: Erratum: ``Isolating Clusters with Wolf-Rayet Stars in I Zw
    18'' (<A href="/abs/2002ApJ...579L..75B">ApJ, 579, L75 [2002]</A>)
Authors: Brown, Thomas M.; Heap, Sara R.; Hubeny, Ivan; Lanz, Thierry;
   Lindler, Don
Bibcode: 2002ApJ...581L.129B
Altcode:
  During publication, the software used to process Figure 1 corrupted
  the Y-axis label. The label should read ``Flux (10<SUP>-16</SUP>
  ergs s<SUP>-1</SUP> cm<SUP>-2</SUP> Å<SUP>-1</SUP>)'' instead of the
  published ``Flux (10<SUP>16</SUP> ergs s<SUP>1</SUP> cm<SUP>2</SUP>
  Å<SUP>1</SUP>).'' The Press sincerely regrets this error.

Title: Observations of Novalike Cataclysmic Variables with the Far
    Ultraviolet Spectroscopic Explorer
Authors: Hoard, D. W.; Szkody, Paula; Linnell, Albert; Long, K.;
   Sion, E. M.; Hubeny, I.; Knigge, C.
Bibcode: 2002AAS...201.3304H
Altcode: 2002BAAS...34.1155H
  Observations at short wavelengths probe the innermost region of
  cataclysmic variables (CVs), at the zone of interaction between the
  accretion flow or disk and the boundary layer and/or white dwarf. We
  present new spectra of three CVs (DW UMa, LS Peg, MV Lyr) obtained
  with the Far Ultraviolet Spectroscopic Explorer satellite. These three
  systems are members of the novalike class of CV, which is characterized
  by high accretion rates and prominent disks. The mean far-UV spectra
  of these three novalike CVs are remarkably different. In addition, our
  time-resolved FUSE spectra of DW UMa may support the recent suggestion
  that a weak white dwarf magnetic field is present in some or all
  novalikes (e.g., the SW Sextantis stars). (Our FUSE observations of
  another CV, the magnetic system YY Dra, will be presented at the AAS
  meeting by A. Linnell, et al.)

Title: Isolating Clusters with Wolf-Rayet Stars in I Zw 18
Authors: Brown, Thomas M.; Heap, Sara R.; Hubeny, Ivan; Lanz, Thierry;
   Lindler, Don
Bibcode: 2002ApJ...579L..75B
Altcode: 2002astro.ph.10089B
  We present UV images and spectra of the starburst galaxy I Zw 18,
  taken with the Space Telescope Imaging Spectrograph. The high
  spatial resolution of these data allows us to isolate clusters
  containing Wolf-Rayet stars of the subtype WC. Our far-UV spectra
  clearly show C IV λλ1548, 1551 and He II λ1640 emission of WC
  stars in two clusters: one within the bright (northwest) half of I
  Zw 18 and one on the outskirts of this region. The latter spectrum
  is unusual because the C IV is seen only in emission, indicating a
  spectrum dominated by WC stars. These data also demonstrate that the
  H I column in I Zw 18 is strongly peaked in the fainter (southeast)
  half of I Zw 18, with a column depth far larger than that reported in
  previous analyses. Based on observations made with the NASA/ESA Hubble
  Space Telescope, obtained at the Space Telescope Science Institute,
  which is operated by the Association of Universities for Research in
  Astronomy, Inc., under NASA contract NAS 5-26555. These observations
  are associated with proposal 9054.

Title: Quasi-molecular lines in Lyman wings of cool DA white
    dwarfs. Application to FUSE observations of G 231-40
Authors: Hébrard, G.; Allard, N. F.; Hubeny, I.; Lacour, S.; Ferlet,
   R.; Vidal-Madjar, A.
Bibcode: 2002A&A...394..647H
Altcode: 2002astro.ph..8372H
  We present new theoretical calculations of the total line profiles
  of Lyman alpha and Lyman beta which include perturbations by both
  neutral hydrogen and protons and all possible quasi-molecular states of
  H<SUB>2</SUB> and H<SUB>2</SUB><SUP>+</SUP>. They are used to improve
  theoretical modeling of synthetic spectra for cool DA white dwarfs. We
  compare them with FUSE observation of G 231-40. The appearance of the
  line wings between Lyman alpha and Lyman beta is shown to be sensitive
  to the relative abundance of hydrogen ions and neutral atoms, and
  thereby to provide a temperature diagnostic for stellar atmospheres
  and laboratory plasmas.

Title: Theoretical Spectral Models of T Dwarfs at Short Wavelengths
    and Their Comparison with Data
Authors: Burrows, Adam; Burgasser, Adam J.; Kirkpatrick, J. Davy;
   Liebert, James; Milsom, J. A.; Sudarsky, D.; Hubeny, I.
Bibcode: 2002ApJ...573..394B
Altcode: 2001astro.ph..9227B
  We have generated new, self-consistent spectral and atmosphere models
  for the effective temperature range 600-1300 K thought to encompass the
  known T dwarfs. For the first time, theoretical models are compared
  with a family of measured T dwarf spectra at wavelengths shortward
  of ~1.0 μm. By defining spectral indices and standard colors in the
  optical and very near-infrared, we explore the theoretical systematics
  with T<SUB>eff</SUB>, gravity, and metallicity. We conclude that the
  short-wavelength range is rich in diagnostics that complement those in
  the near-infrared now used for spectral subtyping. We also conclude that
  the wings of the Na D and K I (7700 Å) resonance lines and aggressive
  rainout of heavy metals (with the resulting enhancement of the sodium
  and potassium abundances at altitude) are required to fit the new
  data shortward of 1.0 μm. Furthermore, we find that the water bands
  weaken with increasing gravity, that modest decreases in metallicity
  enhance the effect in the optical of the sodium and potassium lines,
  and that at low values of T<SUB>eff</SUB>, in a reversal of the
  normal pattern, optical spectra become bluer with further decreases in
  T<SUB>eff</SUB>. Moreover, we conclude that T dwarf subtype is not a
  function of T<SUB>eff</SUB> alone but that it is a nontrivial function
  of gravity and metallicity as well. As do Marley and coworkers in their
  2002 work, we see evidence in early T dwarf atmospheres of a residual
  effect of clouds. With cloudless models, we obtain spectral fits to
  the two late T dwarfs with known parallaxes, but a residual effect
  of clouds on the emergent spectra of even late T dwarfs cannot yet be
  discounted. However, our focus is not on detailed fits to individual
  objects but on the interpretation of the overall spectral and color
  trends of the entire class of T dwarfs, as seen at shorter wavelengths.

Title: Towards a spherical code for the evaluation of solar UV-bands
    that influence the chemical composition in the stratosphere
Authors: Haberreiter, M.; Hubeny, I.; Rozanov, E.; Rüedi, I.; Schmutz,
   W.; Wenzler, T.
Bibcode: 2002ESASP.508..209H
Altcode: 2002soho...11..209H
  We present our analysis of data taken by SUSIM onboard UARS. We
  reconstruct the variability of the UV irradiance and compare it to
  available data. Up to now we model the solar irradiance according to
  the 3-component model by Unruh et al. (1999) based on LTE synthetic
  spectra modeled with Kurucz' ATLAS9 code. Our new approach will be that
  with COSI (COde for Solar Irradiance) we model solar continuum and
  line formation in spherical symmetry and in non-local thermodynamic
  equilibrium (non-LTE). We present our first synthetic solar spectra
  (calculated in LTE) and validate them against spectra computed with
  Kurucz' ATLAS9 code.

Title: Quasi-molecular lines in Lyman wings of cool DA white dwarfs:
    Application to FUSE observations of G231-40
Authors: Hébrard, G.; Allard, N. F.; Hubeny, I.; Lacour, S.; Ferlet,
   R.; Vidal-Madjar, A.
Bibcode: 2002sf2a.conf..527H
Altcode:
  Comprehensive, calculations of the Lyman-alpha and Lyman-beta line wings
  which include perturbations by both neutral hydrogen and protons and
  all possible quasi-molecular states of H2 and H2+ are used to predict
  synthetic spectra for cool DA white dwarfs. They are compared with
  FUSE observation of G231-40. The appearance of the line wings between
  Lyman-alpha and Lyman-beta is shown to be sensitive to the relative
  abundance of hydrogen ions and neutral atoms, and thereby to provide
  a temperature diagnostic for stellar atmospheres and laboratory plamas.

Title: Lyman gamma satellites due to H-H+ collisions: Application
    to FUSE observations of hot white dwarfs
Authors: Bourdreux, S.; Allard, N.; Kielkopf, J.; Desert, J. -M.;
   Hebrard, G.; Hubeny, I.; Peek, J.; Ferlet, R.; Vidal-Madjar, A.
Bibcode: 2002sf2a.conf..509B
Altcode:
  Lyman gamma profiles perturbed by protons using molecular potential
  of Peek allow us to identificate a large feature near 995 A in FUSE
  observations of hot white dwarfs. It is visible also in the HUT
  spectrum of Wolf1346 and in some ORFEUS spectra. This feature is due
  to Quasi-molecular Lyman gamma satellites due to H-H+ collisions near
  991 and 996A.

Title: A High S/N View of the Photosphere of the Hot White Dwarf
    G191-B2B from STIS
Authors: Holberg, J. B.; Barstow, M. A.; Hubeny, I.; Sahu, M. S.;
   Bruhweiler, F. C.; Landsman, W. B.
Bibcode: 2002AAS...200.7205H
Altcode: 2002BAAS...34..765H
  We have assembled a unique, high signal-to-noise (S/N) spectrum of
  the hot metal-rich DA white dwarf, G191-B2B, from a coaddition of 22
  E140H and 40 E230H STIS calibration spectra. This superb data set fully
  covers the wavelength range from 1155 A to 3169 A with S/N ranging from
  over 100 to 30; affording an unprecedentedly detailed view of the UV
  stellar absorption lines in a white dwarf star. We use this spectrum
  to search for a number of previously undiscovered heavy elements in
  the G191-B2B photosphere and to estimate elemental abundances and
  place upper limits on the abundances of a number of key species. An
  accurate photospheric inventory of heavy elements in hot degenerate
  stars is basic to our understanding of the chemical diffusion in these
  stars. These observations highlight the wealth of information present
  in echelle resolution spectra of white dwarfs such as G191-B2B and
  the need for a succeeding generation of UV instrumentation capable
  of providing data of this type for other degenerate stars. This work
  funded by STScI Grant AR 9202.

Title: Multidimensional Non-LTE Radiative Transfer. I. A Universal
    Two-dimensional Short-Characteristics Scheme for Cartesian, Spherical,
    and Cylindrical Coordinate Systems
Authors: van Noort, Michiel; Hubeny, Ivan; Lanz, Thierry
Bibcode: 2002ApJ...568.1066V
Altcode:
  We have developed an efficient and robust two-dimensional non-LTE
  radiation transfer solver appropriate for line transfer in the
  equivalent two-level atom formalism. The numerical method applies
  the accelerated lambda iteration technique together with the
  short-characteristics scheme. The code presented in this paper
  incorporates all three standard geometries (Cartesian, cylindrical,
  and spherical) in a transparent way while allowing for arbitrary
  (three-dimensional) velocity fields. The geometry-specific parts of
  the radiative transfer solver are modularized so that the change of
  geometry is accomplished by simply setting the appropriate switch. We
  have also developed a parallel version of the code, in which we
  use a parallelization in spatial subdomains, and showed that such a
  scheme is sufficiently robust. We have performed a number of tests
  of the performance of the solver in all three geometries. Finally,
  we discuss the internal accuracy of the transfer solutions depending
  on the number of spatial, angular, and frequency grid points.

Title: FUSE observations of PG1342+444: new insights into the nature
    of the hottest DA white dwarfs
Authors: Barstow, M. A.; Good, S. A.; Holberg, J. B.; Burleigh, M. R.;
   Bannister, N. P.; Hubeny, I.; Napiwotzki, R.
Bibcode: 2002MNRAS.330..425B
Altcode:
  We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations
  of the very hot (T<SUB>eff</SUB>~60000K) DA white dwarf PG1342+444,
  describing our data reduction and analysis techniques. The spectrum
  reveals a number of photospheric absorption lines from high ionization
  species along with numerous interstellar features. The photospheric
  detections include the 1031.9- and 1037.0-Å OVI lines which are seen
  for the first time in a hot DA atmosphere and are usually associated
  with the much hotter PG1159 stars and so-called OVI central stars
  of planetary nebulae. Estimates of the stellar effective temperature
  made independently using both the Balmer and Lyman series lines are
  in disagreement (T<SUB>eff</SUB>~67000 and ~54000K respectively),
  when taking into account just the statistical uncertainties in the
  analyses. However, the presence of weak absorption from the CIII
  multiplet near 1176Å, which is predicted to be much stronger if the
  star were as cool as the Lyman measurement suggests, leads us to favour
  the higher temperature. PG1342+444 appears to have enhanced C, Fe and Ni
  abundances in its atmosphere compared with all the other G191-B2B-like
  DA white dwarfs, which might affect the temperature structure of the
  atmosphere if not homogeneously distributed, as assumed in this study.

Title: HST STIS spectroscopy of VW Hydri during early quiescence
    following a superoutburst
Authors: Sion, E. M.; Cheng, F. -H.; Szkody, P.; Gänsicke, B. T.;
   Sparks, W. M.; Hubeny, I.
Bibcode: 2002ASPC..261...69S
Altcode: 2002pcvr.conf...69S
  We have obtained two Hubble Space Telescope STIS spectra of the
  SU UMa-type dwarf nova VW Hydri at two points in early quiescence
  following a superoutburst. Multi-spectral component model fitting to
  the data reveals a 23 000 K heated white dwarf with chemical abundances
  indicative of nucleosynthetic processing (supporting a link between
  dwarf novae and classical novae), and a rotation of 400 km/s. Our
  best-fit models result when a rapidly spinning accretion belt with
  solar composition is present in addition to the cooler, more slowly
  rotating photosphere.

Title: The Origin of Hot Subluminous Horizontal-Branch Stars in ω
    Centauri and NGC 2808
Authors: Sweigart, A. V.; Brown, T. M.; Lanz, T.; Landsman, W. B.;
   Hubeny, I.
Bibcode: 2002ASPC..265..261S
Altcode: 2002ocuw.conf..261S; 2002astro.ph..3063S
  Hot subluminous stars lying up to 0.7 mag below the extreme horizontal
  branch (EHB) are found in the UV color-magnitude diagrams of omega Cen
  and NGC 2808. Such stars are unexplained by canonical HB theory. In
  order to explore the origin of these subluminous stars, we evolved a
  set of low-mass stars from the main sequence through the helium-core
  flash to the HB for a wide range in the mass loss along the red-giant
  branch (RGB). Stars with the largest mass loss evolve off the RGB to
  high effective temperatures before igniting helium in their cores. Our
  results indicate that the subluminous EHB stars, as well as the gap
  within the EHB of NGC 2808, can be explained if these stars undergo
  a late helium-core flash on the white-dwarf cooling curve. Under
  these conditions the flash convection will penetrate into the stellar
  envelope, thereby mixing most, if not all, of the envelope hydrogen
  into the hot helium- burning interior. This phenomenon is analogous
  to the "born-again" scenario for producing hydrogen-deficient stars
  during a very late helium-shell flash. "Flash mixing" greatly enhances
  the envelope helium and carbon abundances and, as a result, leads to
  an abrupt increase in the HB effective temperature. We argue that
  the EHB gap in NGC 2808 is caused by this theoretically predicted
  dichotomy in the HB morphology. Using new helium- and carbon-rich
  stellar atmospheres, we show that the flash-mixed stars have the same
  reduced UV flux as the subluminous EHB stars. Moreover, we demonstrate
  that models without flash mixing lie, at most, ~0.1 mag below the EHB
  and hence fail to explain the observations. Flash mixing may also
  provide a new evolutionary channel for producing the high gravity,
  He-rich sdO and sdB stars.

Title: The D/H Abundance Ratio in Local Interstellar Gas
Authors: Sahu, M. S.; Landsman, W.; Bruhweiler, F. C.; Holberg, J.;
   Hubeny, I.; Barstow, M.; Linsky, J.; Gull, T.; Lindler, D.; Lanz,
   T.; Feggans, K.
Bibcode: 2001AAS...199.1101S
Altcode: 2001BAAS...33.1323S
  Variations of the D/H ratio on scales of 100 pc are important for two
  reasons: (1) they complicate the use of deuterium as a cosmological
  probe, and (2) they imply non-uniform deuterium production/destruction
  and an inefficient mixing of interstellar gas. The Local Interstellar
  Medium (LISM) is an ideal location to test whether the D/H abundance
  ratio varies or not, because the heating sources and radiation
  fields are well-studied and we have a detailed knowledge of the
  three-dimensional (3D) structure of the diffuse clouds in the LISM. This
  detailed knowledge of the number, structure and velocities of the
  absorbing clouds greatly helps in reducing errors in the derived
  D/H ratios. We are working on a project to obtain high-precision
  D/H abundance ratios in the interstellar gas within 100 pc. For this
  purpose, we primarily use HST-STIS data towards nearby hot, white dwarfs
  (WDs). We have also begun an HST archival research project to study
  about 20 WD sightlines. In this poster, we present new STIS observations
  for GD 153 and HZ 43 and report the results of our HST Archival project.

Title: The Origin of Hot Subluminous Horizontal-Branch Stars in ω
    Cen and NGC 2808
Authors: Sweigart, A. V.; Brown, T. M.; Moehler, S.; Lanz, T.;
   Landsman, W. B.; Hubeny, I.; Dreizler, S.; Napiwotzki, R.
Bibcode: 2001AAS...19913704S
Altcode: 2001BAAS...33.1512S
  Ultraviolet (UV) observations of the globular clusters ω Cen and NGC
  2808 have revealed an unexpected population of hot subluminous stars
  lying up to 0.7 mag below the extreme horizontal branch (EHB) in the
  UV, which are not explained by canonical stellar models. In order to
  explore the evolutionary status of these stars, we have evolved a set
  of low-mass stars from the main sequence through the helium flash to
  the horizontal branch (HB) for a wide range in the mass loss along the
  red-giant branch (RGB). Stars with the largest mass loss evolve off
  the RGB to high effective temperatures before igniting helium in their
  cores. Our results indicate that the subluminous stars can be explained
  if these stars undergo a late helium flash while descending the white
  dwarf cooling curve. Under these conditions the convection zone produced
  by the helium flash will penetrate into the stellar envelope, thereby
  mixing the envelope hydrogen into the hot helium-burning interior, where
  it is rapidly consumed. Such ``flash-mixed'' stars will have helium-
  and carbon-rich envelopes and will lie at higher effective temperatures
  than the hottest canonical (i.e., unmixed) EHB stars. Using new stellar
  atmospheres, we show that these changes in the envelope abundances
  will suppress the UV flux in the spectra of the flash-mixed stars by
  the amount needed to explain the hot subluminous stars in ω Cen and
  NGC 2808. To test this evolutionary scenario, we have obtained medium
  resolution spectra of a sample of the hottest HB stars in ω Cen. We
  find that these stars are indeed helium-rich compared to classical
  EHB stars and also considerably hotter than the hottest EHB models
  without flash mixing.

Title: Non-LTE, Relativistic Accretion Disk Fits to 3C 273 and the
    Origin of the Lyman Limit Spectral Break
Authors: Blaes, Omer; Hubeny, Ivan; Agol, Eric; Krolik, Julian H.
Bibcode: 2001ApJ...563..560B
Altcode: 2001astro.ph..8451B
  We fit general relativistic, geometrically thin accretion disk models
  with non-LTE atmospheres to near-simultaneous multiwavelength data of
  3C 273, extending from the optical to the far-ultraviolet. Our model
  fits show no flux discontinuity associated with a hydrogen Lyman edge,
  but they do exhibit a spectral break which qualitatively resembles that
  seen in the data. This break arises from relativistic smearing of Lyman
  emission edges which are produced locally at tens of gravitational radii
  in the disk. We discuss the possible effects of metal line blanketing on
  the model spectra, as well as the substantial Comptonization required
  to explain the observed soft X-ray excess. Our best-fit accretion
  disk model underpredicts the near-ultraviolet emission in this source
  and also has an optical spectrum which is too red. We discuss some of
  the remaining physical uncertainties and suggest in particular that
  an extension of our models to the slim disk regime and/or including
  nonzero magnetic torques across the innermost stable circular orbit
  may help resolve these discrepancies.

Title: NLTE Models of Vertical structure of Accretion Disks around
    Stellar Mass Black Holes
Authors: Hubeny, I.; Blaes, O.; Krolik, J. H.; Agol, E.; Lanz, T.
Bibcode: 2001AAS...19915908H
Altcode: 2002BAAS...34Q.569H
  Recent upgrades of our computer program TLUSDISK are briefly
  described. These include a self-consistent treatment of Compton
  scattering, and the effects of X-ray continuum opacities of the most
  important metal species (C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni). In the
  case the central degenerate object is a neutron star or a black hole,
  we allow for a full general relativistic treatment. We show the effects
  of Comptonization and metal opacities on the structure of disk under
  various conditions. We also present a simple analytic prescription
  for the vertical temperature structure of the disk in the presence
  of Comptonization, and show under what conditions a hot outer layer
  (a corona) is formed.

Title: Solar UV Radiation and the Origin of Life on Earth
Authors: Heap, S. R.; Gaidos, E.; Hubeny, I.; Lanz, T. M.
Bibcode: 2001AAS...199.0314H
Altcode: 2001BAAS...33.1305H
  We have embarked on a program aimed at understanding the atmosphere of
  the early Earth, because of its importance as a greenhouse, radiation
  shield, and energy source for life. Here, we give a progress report on
  the first phase of this program: to establish the UV radiation from
  the early Sun. We are presently obtaining ultraviolet spectra (STIS,
  FUSE, EUVE) of carefully selected nearby, young solar-type stars,
  which act as surrogates for the early Sun. We are currently making
  detailed non-LTE analyses of the spectra and constructing models of
  their photospheres + chromospheres. Once validated, these models will
  allow us to extrapolate our theoretical spectra to unobserved spectral
  regions, and to proceed to the next step: to develop photochemical
  models of the pre-biotic and Archean atmosphere of the Earth.

Title: NLTE Model Atmospheres of Supersoft X-Ray Sources
Authors: Lanz, T.; Hubeny, I.
Bibcode: 2001AAS...199.1712L
Altcode: 2001BAAS...33.1336L
  Supersoft X-Ray Sources are most probably very hot white dwarfs
  undergoing steady nuclear burning in their envelopes. They are high
  luminosity (L &gt; 0.1 L<SUB></SUB> Edd), soft (kT≈ 50 eV) low
  mass binary with a white dwarf primary accreting at a sub-Eddington
  rate. High-resolution spectra in the soft X-rays are now becoming
  available with Chandra and XMM-Newton. Photospheric line spectroscopy
  has the potential to provide accurate diagnostics of the white dwarf
  properties. We have therefore embarked on a project aimed at providing
  new NLTE model atmospheres of supersoft sources. We are building a
  series of model atmospheres of hot white dwarfs (20&lt;= kT&lt;= 100
  eV; 8&lt;= log g&lt;= 10) with various surface composition. The models
  incorporate the most abundant species, H, He, C, N, O, Ne, Mg, Si, S,
  and Fe, which are allowed to depart from Saha-Boltzmann statitics. Our
  models include the influence of multi-level model atoms, metal line
  blanketing, and Auger ionization on the atmospheric structure. A
  preliminary comparison of models calculated assuming coherent (Thomson)
  and non-coherent (Compton) scattering is presented. This work was
  supported through a NASA ATP grant (NRA 00-01-ATP-153).

Title: Hubble Space Telescope STIS Spectroscopy of VW Hydri during
    Early Quiescence following a Superoutburst
Authors: Sion, Edward M.; Cheng, Fu-Hua; Szkody, Paula; Gänsicke,
   Boris; Sparks, Warren M.; Hubeny, Ivan
Bibcode: 2001ApJ...561L.127S
Altcode:
  Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS)
  observations of VW Hydri 2 and 7 days after the end of a superoutburst
  reveal a heated white dwarf with deep broad Lyα, narrow metallic
  absorption features and evidence of a hotter Keplerian-broadened
  component. We confirm the existence of enhanced abundances of
  odd-numbered nuclear species P, Mn, and Al as well as an N/C
  ratio indicative of CNO H-burning thermonuclear processing. Our
  best single-temperature white dwarf reduced χ<SUP>2</SUP>
  fit to the first spectrum reveals (1) a DAZQ white dwarf with
  T<SUB>eff</SUB>=22,500+/-500 K, logg=8.0, and photospheric abundances
  C=0.3 solar, N=3.0 solar, O=3.0 solar, Si=0.3 solar, Al=2 solar,
  Fe=0.5 solar, Mg=3.0 solar, Mn=50 solar, Ni=0.3 solar, P=15 solar, and
  Ti=0.1 solar. The best-fit white dwarf + accretion belt composite model
  yields a large improvement in the reduced χ<SUP>2</SUP> value. The
  accretion belt temperature is 32,000 K and covers a fractional area
  of 3%, contributing 11% of the flux. The second spectrum 5 days later
  reveals slightly increased metal abundances except that P is elevated
  to 20 times solar while Fe has declined to 0.05 times solar. The
  white dwarf has cooled by ~1000 K, the belt temperature is 32,000 K,
  and the fractional area and flux contribution of the belt are 5%
  and 20%, respectively. These STIS observations confirm that a past
  (prehistoric?) thermonuclear runaway has occurred on the white dwarf in
  VW Hyi. It is expected that the thermonuclear runaway would be strong
  enough to produce a nova outburst. Therefore, these two classes of
  close binaries, namely, dwarf novae and classical novae, are linked
  and can overlap.

Title: A comparison of DA white dwarf temperatures and gravities
    from Lyman and Balmer line studies
Authors: Barstow, M. A.; Holberg, J. B.; Hubeny, I.; Good, S. A.;
   Levan, A. J.; Meru, F.
Bibcode: 2001MNRAS.328..211B
Altcode: 2001astro.ph..7529B
  We present measurements of the effective temperatures and surface
  gravities for a sample of hot DA white dwarfs, using the Lyman line data
  available from the HUT, ORFEUS and FUSE FUV space missions. Comparing
  the results with those from the standard Balmer line technique, we
  find that there is a general good overall agreement between the two
  methods. However, significant differences are found for a number of
  stars, but not always of a consistent nature in that sometimes the
  Balmer temperature exceeds that derived from the Lyman lines and
  in other instances it is lower. We conclude that, with the latest
  model atmosphere calculations, these discrepancies probably do not
  arise from an inadequate theoretical treatment of the Lyman lines but
  rather from systematic effects in the observation and data reduction
  processes, which dominate the statistical errors in these spectra. If
  these systematic data reduction effects can be adequately controlled,
  the Lyman line temperature and gravity measurements are consistent
  with those obtained from the Balmer lines when allowance is made for
  reasonable observational uncertainties.

Title: Flash Mixing on the White Dwarf Cooling Curve: Understanding
    Hot Horizontal Branch Anomalies in NGC 2808
Authors: Brown, Thomas M.; Sweigart, Allen V.; Lanz, Thierry; Landsman,
   Wayne B.; Hubeny, Ivan
Bibcode: 2001ApJ...562..368B
Altcode: 2001astro.ph..8040B
  We present an ultraviolet color-magnitude diagram (CMD) spanning
  the hot horizontal branch (HB), blue straggler, and white dwarf
  populations of the globular cluster NGC 2808. These data were obtained
  with the far-UV and near-UV cameras on the Space Telescope Imaging
  Spectrograph (STIS). Although previous optical CMDs of NGC 2808 show
  a high-temperature gap within the hot HB population, no such gap is
  evident in our UV CMD. Instead, we find a population of hot subluminous
  HB stars, an anomaly only previously reported for the globular cluster
  ω Cen. Our theoretical modeling indicates that the location of these
  subluminous stars in the UV CMD, as well as the high-temperature gap
  along the HB in optical CMDs, can be explained if these stars underwent
  a late helium-core flash while descending the white dwarf cooling
  curve. We show that the convection zone produced by such a late helium
  flash will penetrate into the hydrogen envelope, thereby mixing hydrogen
  into the hot helium-burning interior, where it is rapidly consumed. This
  phenomenon is analogous to the ``born again'' scenario for producing
  hydrogen-deficient stars following a late helium-shell flash. The
  flash mixing of the envelope greatly enhances the envelope helium and
  carbon abundances, and leads, in turn, to a discontinuous increase in
  the HB effective temperatures at the transition between canonical and
  flash-mixed stars. We argue that the hot HB gap is associated with this
  theoretically predicted dichotomy in the HB properties. Moreover, the
  changes in the emergent spectral energy distribution caused by these
  abundance changes are primarily responsible for explaining the hot
  subluminous HB stars. Although further evidence is needed to confirm
  that a late helium-core flash can account for the subluminous HB stars
  and the hot HB gap, we demonstrate that an understanding of these stars
  requires the use of appropriate theoretical models for their evolution,
  atmospheres, and spectra. Based on observations with the NASA/ESA Hubble
  Space Telescope obtained at the Space Telescope Science Institute,
  which is operated by AURA, Inc., under NASA contract NAS5-26555.

Title: Non-LTE Models and Theoretical Spectra of Accretion Disks
    in Active Galactic Nuclei. IV. Effects of Compton Scattering and
    Metal Opacities
Authors: Hubeny, Ivan; Blaes, Omer; Krolik, Julian H.; Agol, Eric
Bibcode: 2001ApJ...559..680H
Altcode: 2001astro.ph..5507H
  We extend our models of the vertical structure and emergent radiation
  field of accretion disks around supermassive black holes described
  in previous papers of this series. Our models now include both a
  self-consistent treatment of Compton scattering and the effects of
  continuum opacities of the most important metal species (C, N, O,
  Ne, Mg, Si, S, Ar, Ca, Fe, Ni). With these new effects incorporated,
  we compute the predicted spectrum from black holes accreting at nearly
  the Eddington luminosity (L/L<SUB>Edd</SUB>~0.3) and central masses of
  10<SUP>6</SUP>, 10<SUP>7</SUP>, and 10<SUP>8</SUP> M<SUB>solar</SUB>. We
  also consider two values of the Shakura-Sunyaev α parameter, 0.1 and
  0.01, but in contrast to our previous papers, we consider a kinematic
  viscosity that is independent of depth. Although it has little effect
  when M&gt;10<SUP>8</SUP> M<SUB>solar</SUB>, Comptonization grows in
  importance as the central mass decreases and the central temperature
  rises. It generally produces an increase in temperature with height
  in the uppermost layers of hot atmospheres. Compared to models
  with coherent electron scattering, Comptonized models have enhanced
  extreme ultraviolet/soft X-ray emission, but they also have a more
  sharply declining spectrum at very high frequencies. Comptonization
  also smears the hydrogen and the He II Lyman edges. The effects
  of metals on the overall spectral energy distribution are smaller
  than the effects of Comptonization for these parameters. Compared to
  pure hydrogen-helium models, models with metal-continuum opacities
  have reduced flux in the high-frequency tail, except at the highest
  frequencies, where the flux is very low. Metal photoionization edges
  are not present in the overall disk-integrated model spectra. The
  viscosity parameter α has a more dramatic effect on the emergent
  spectrum than do metal-continuum opacities. As α increases (and
  therefore the disk column density decreases), the flux at both the high-
  and low-frequency extremes of the spectrum increases, while the flux
  near the peak decreases. Multitemperature blackbodies are a very poor
  approximation to accretion disk spectra in the soft X-ray region, and
  such crude modeling may greatly overestimate the accretion luminosity
  required to explain observed soft X-ray excesses in active galactic
  nuclei. In addition to our new grid of models, we also present a
  simple analytic prescription for the vertical temperature structure
  of the disk in the presence of Comptonization, and show under what
  conditions a hot outer layer (a corona) is formed.

Title: Far-ultraviolet spectroscopy of the hot DA white dwarf WD
    2218+706 (DeHt5) with STIS
Authors: Barstow, M. A.; Bannister, N. P.; Holberg, J. B.; Hubeny,
   I.; Bruhweiler, F. C.; Napiwotzki, R.
Bibcode: 2001MNRAS.325.1149B
Altcode: 2000astro.ph..1172B
  We report a study of the photospheric composition of the hot DAQ3 white
  dwarf WD 2218+706, which is also the central star of the old planetary
  nebula DeHt5. Helium is detected in the far-UV spectrumQ4. In addition,
  the star clearly contains significant quantities of elements heavier
  than He at abundances generally a factor of 2 to 10 higher than those
  found in the archetypal heavy element-rich DA G191-B2B. This is the
  first detection of trace He using the Heii λ1640 line in an isolated
  DA white dwarf, but the low surface gravity is more indicative of a
  binary evolution route from the red giant branch rather than a path
  along the asymptotic giant branch (AGB) as a single star. However,
  the absence of any evidence for a companion star and the uncertainty
  in the measured mass for WD 2218+706 still allow the possibility of
  an origin along an AGB evolutionary track. We reanalyse the existing
  optical spectra of WD 2218+706 using our latest pure H and heavy
  element-rich model atmospheres, obtaining a good match between the
  observed and synthetic spectra with either set of models. We find
  little evidence of any inconsistency in the temperature required to
  fit individual Balmer lines, as reported elsewhere for this star. Any
  discrepancies we see are confined to the Hα line and the core of Hβ
  but they do not compromise our analysis.

Title: HST/STIS spectroscopy of the exposed white dwarf in the
    short-period dwarf nova EK TrA
Authors: Gänsicke, B. T.; Szkody, P.; Sion, E. M.; Hoard, D. W.;
   Howell, S.; Cheng, F. H.; Hubeny, I.
Bibcode: 2001A&A...374..656G
Altcode: 2001astro.ph..6023G
  We present high resolution Hubble Space Telescope ultraviolet
  spectroscopy of the dwarf nova EK TrA obtained in deep
  quiescence. The Space Telescope Imaging Spectrograph data reveal
  the broad Lyalpha absorption profile typical of a moderately cool
  white dwarf, overlayed by numerous broad emission lines of He, C,
  N, and Si and by a number of narrow absorption lines, mainly of
  \C I and \Si II. Assuming a white dwarf mass in the range 0.3-1.4
  M<SUB>sun</SUB> we derive T<SUB>eff</SUB>=17 500-23 400 K for the
  primary in EK TrA; T<SUB>eff</SUB> =18 800 K for a canonical mass of
  0.6 M<SUB>sun</SUB>. From the narrow photospheric absorption lines,
  we measure the white dwarf rotational velocity, vsin i=200+/-100
  km s<SUP>-1</SUP>. Even though the strong contamination of the
  photospheric white dwarf absorption spectrum by the emission lines
  prevents a detailed quantitative analysis of the chemical abundances
  of the atmosphere, the available data suggest slightly sub-solar
  abundances. The high time resolution of the STIS data allows us to
  associate the observed ultraviolet flickering with the emission lines,
  possibly originating in a hot optically thin corona above the cold
  accretion disk. Based on observations made with the NASA/ESA Hubble
  Space Telescope, obtained at the Space Telescope Science Institute,
  which is operated by the Association of Universities for Research in
  Astronomy, Inc., under NASA contract NAS 5-26555.

Title: Understanding Horizontal Branch Anomalies in NGC 2808
Authors: Brown, T. M.; Sweigart, A. V.; Lanz, T.; Landsman, W. B.;
   Hubeny, I.
Bibcode: 2001AAS...198.4302B
Altcode: 2001BAAS...33..844B
  We present an ultraviolet color-magnitude diagram (CMD) spanning the hot
  horizontal branch (HB), blue straggler, and white dwarf populations
  of the globular cluster NGC 2808. These data, obtained with the
  Space Telescope Imaging Spectrograph (STIS), demonstrate that NGC
  2808 harbors a significant population of hot subluminous HB stars,
  an anomaly only previously reported for the globular cluster Omega
  Cen. Our theoretical modeling indicates that the location of these
  subluminous stars in the CMD, as well as the high temperature gap along
  the HB of NGC 2808, can be explained if these stars underwent a late
  helium-core flash while descending the white dwarf cooling curve. We
  show that the convective zone produced by such a late helium flash will
  penetrate into the hydrogen envelope, thereby mixing hydrogen into
  the hot helium-burning interior, where it is rapidly consumed. This
  phenomenon is analogous to the "born again" scenario for producing
  hydrogen-deficient stars following a late helium-shell flash. The flash
  mixing of the envelope greatly enhances the envelope helium and carbon
  abundances that, in turn, leads to a discontinuous increase in the HB
  effective temperatures. We argue that the hot HB gap is associated with
  this theoretically predicted dichotomy in the HB properties. Moreover,
  the changes in the emergent spectral energy distribution caused by
  these abundance changes are primarily responsible for explaining
  the hot subluminous HB stars. Although further evidence is needed to
  confirm that a late helium-core flash can account for the subluminous HB
  stars and the hot HB gap, we demonstrate that an understanding of these
  stars requires use of sophisticated models for the stellar evolution,
  atmospheres, and synthetic spectra.

Title: Heavy Elements in DA White Dwarfs
Authors: Barstow, M. A.; Burleigh, M. R.; Bannister, N. P.; Holberg,
   J. B.; Hubeny, I.; Bruhweiler, F. C.; Napiwotzki, R.
Bibcode: 2001ASPC..226..128B
Altcode: 2001ewwd.work..128B
  No abstract at ADS

Title: Preface (Interacting astronomers: a symposium on Mirek Plavec's
    favorite stars. Proceedings)
Authors: Hubeny, Ivan; Malkan, Matt
Bibcode: 2001PAICz..89D...5H
Altcode:
  No abstract at ADS

Title: FUSE Observations of the Hottest DA White Dwarfs
Authors: Barstow, M. A.; Burleigh, M. R.; Bannister, N. P.; Holberg,
   J. B.; Hubeny, I.
Bibcode: 2001ASPC..226...94B
Altcode: 2000astro.ph.10447B; 2001ewwd.work...94B
  We report early FUSE observations of the very hot DA white dwarfs
  PG1342+444 and REJ0558-371. Detection of photospheric absorption lines
  allows us to estimate the abundances of C, O, Si, P, S and Fe, the first
  measurements reported for DA stars at such high temperatures. Values
  of Teff and log g determined for PG1342+444 from the Lyman line series
  disagree with the results of the standard Balmer line analysis, an
  issue that requires further investigation.

Title: NLTE Model Atmospheres for OB Stars
Authors: Lanz, Thierry; Hubeny, Ivan
Bibcode: 2001ASPC..247..351L
Altcode: 2001scpp.conf..351L
  No abstract at ADS

Title: From Escape Probabilities to Exact Radiative Transfer
Authors: Hubeny, Ivan
Bibcode: 2001ASPC..247..197H
Altcode: 2001scpp.conf..197H
  No abstract at ADS

Title: From stars to quasars. Modeling radiation-dominated objects
    in astrophysics
Authors: Hubeny, Ivan
Bibcode: 2001PAICz..89....1H
Altcode:
  There is a whole class of astronomical objects for which radiation is
  not only a probe of the physical state, but is in fact an important
  energy balance agent. In these objects, radiative transfer plays
  a crucial role. Typical examples of such a situation are stellar
  atmospheres, interstellar matter and various structures within,
  and accretion disks, both around stellar mass degenerate objects
  (cataclysmic variables), and around supermassive black holes
  (quasars). We concentrate on two objects - stellar atmospheres and
  quasar accretion disks, and show that since they have many similarities
  they can be modeled using an analogous approach. We will give a
  brief overview of recent progress in their modeling. On the stellar
  atmospheres side, very sophisticated non-LTE models including millions
  of lines are now being constructed. It is shown that they provide an
  excellent match to high-quality ground- and space-based spectra. In
  quasar modeling, we have constructed a grid of non-LTE disk models for
  a wide range of parameters, and begun a study of analysing observed
  data using the new models.

Title: Interacting astronomers: a symposium on Mirek Plavec's favorite
    stars. Proceedings
Authors: Harmanec, P.; Hadrava, P.; Hubeny, I.
Bibcode: 2001PAICz..89.....H
Altcode:
  No abstract at ADS

Title: Properties of the z = 2.73 galaxy, MS1512-cB58
Authors: Heap, Sara R.; Hubeny, Ivan; Lanz, Thierry M.
Bibcode: 2001ApSSS.277..263H
Altcode:
  MS1512-cB58 is an z=2.73 galaxy whose apparent brightness is amplified
  by30-50X due to gravitationally lensing. The restframe far-UV spectrum
  of cB58 that was obtained by Keck-I/LRIS is `one of the best ultraviolet
  spectra of a starburst galaxy obtained at any redshift' (Pettini et
  al., 2000). We have analyzed and modeled the spectrum of this galaxy in
  order to learn the properties of high-redshift galaxies. We find that
  our model spectrum is a near match to the observed spectrum of cB58 if
  the galaxy has a SMC-like metallicity, and has a Salpeter IMF extending
  up to ~ 100 M. The spectrum of cB58 also shows many absorption lines
  formed in a giant, expanding gas shell surrounding the star-forming
  complex. We show preliminary findings of the properties of the giant
  HII region based on our CLOUDSPEC model.

Title: STIS Observations of the Photospheric Stratification of Heavy
    Elements in Hot DA White Dwarfs
Authors: Holberg, J. B.; Barstow, M. A.; Bruhweiler, F. C.; Hubeny, I.
Bibcode: 2000AAS...197.8304H
Altcode: 2000BAAS...32.1543H
  We present results from echelle spectra obtained with the Space
  Telescope Imaging Spectrograph (STIS) of the hot DA white dwarfs, GD 659
  (WD0050-332) and GD 246 (WD2309+105), which provide new information on
  the occurrence of heavy elements in the photospheres of these stars. In
  the case of GD 659, we show that the C IV, N V and Si IV resonance
  lines, previously observed with IUE, and thought to be interstellar or
  circumstellar in origin, are in fact photospheric in nature. Further,
  the strength of the highly excited N V lines in a star as cool as GD
  659 (T<SUB>eff</SUB> = 35,300 K) can be explained only if the nitrogen
  is stratified in the stellar photosphere. Thus, GD 659 is apparently
  similar to REJ 1032+532 and perhaps REJ 1614-085, which also show super
  nitrogen abundances, and have photospheres with stratified N abundances.

Title: GALSPEC: A Tool for Computing the Spectra of Star-Forming
    Galaxies of Low Metallicity
Authors: Heap, S. R.; Hubeny, I.; Lanz, T. M.; Lindler, D. J.
Bibcode: 2000AAS...197.7813H
Altcode: 2000BAAS...32R1531H
  The far-ultraviolet spectral region is rich in diagnostics of
  star formation in galaxies; it gives information not only about the
  star-forming complex, but also about the dust and circumstellar gas. We
  have therefore developed a tool, called GALSPEC, for computing far-UV
  spectra of star-forming galaxies. The user controls the process through
  a graphical user interface (GUI) by specifying the input parameters for
  the stars, dust, and gas. GALSPEC computes the integrated spectrum of a
  star-forming complex, given the rate of star formation, metallicity (0.2
  Z<SUB>sun</SUB> or 0.5 Z<SUB>sun</SUB>), and IMF upper mass limit. To
  compute the integrated spectrum, GALSPEC makes use of a library
  of stellar spectra composed of observed spectra from HST and model
  spectra calculated with the TLUSTY/SYNSPEC program (Hubeny &amp; Lanz
  1995). GALSPEC then applies wavelength-dependent extinction according
  to Calzetti's starburst extinction law. The mechanical luminosity from
  massive stars and supernovae sweeps up interstellar material thereby
  forming an expanding shell with a central cavity. GALSPEC computes the
  absorption spectrum of the shell using the CLOUDSPEC program (Hubeny
  2000), a combination of Ferland's CLOUDY program and SYNSPEC. This work
  was supported by the STIS GTO program at Goddard and by STScI grants
  (GO 7437, AR 7985).

Title: A New Grid of NLTE Model Atmospheres of Hot Stars
Authors: Hubeny, I.; Lanz, T.
Bibcode: 2000AAS...197.7812H
Altcode: 2000BAAS...32Q1531H
  We briefly describe improvements in our non-LTE model atmosphere code,
  TLUSTY. The upgrades include opacity sampling, improved Fe collisional
  strengths, resonance-averaged photoionization cross-sections, and a
  number of numerical enhancements. Using TLUSTY, version 200, we have
  calculated a grid of NLTE, fully-blanketed, model atmospheres covering
  the range of O to early B-type stars ( 20000 &lt;= T<SUB></SUB> eff
  &lt;= 55000 K, 3.0 &lt;= log g &lt;= 4.75) with a solar or 1/5 solar
  metallicity. The models incorporate over 70,000 NLTE atomic levels of
  about 30 ions of H, He, C, N, O, Ne, Mg, Si, S, Fe and Ni, which are
  grouped into about 700 superlevels. We compare our predicted EUV fluxes
  to other existing grids of model atmospheres (Atlas9, CoStar models), as
  well as to actual UV and optical observations of representative stars.

Title: The D/H Abundance Ratio in Local Interstellar Gas
Authors: Sahu, M. S.; Landsman, W.; Bruhweiler, F. C.; Linsky, J.;
   Hubeny, I.; Barstow, M.; Holberg, J.; Gull, T.; Bowers, C.; Lindler,
   D.; Lanz, T.; Feggans, K.
Bibcode: 2000AAS...197.0703S
Altcode: 2000AAS...197..703S; 2000BAAS...32.1401S
  Does the D/H ratio vary within ~ 100 pc of the Sun? If it does, what
  is the range of these variations? Are the D/H variations correlated to
  any physical property of the absorbing cloud? To answer these questions
  we have begun a project to obtain high-precision D/H abundance ratios
  in the Local Interstellar Medium within ~ 100 pc (Sahu et al. 1999,
  ApJ 523, L159). For this purpose, we primarily use HST-Space Telescope
  Imaging Spectrograph (STIS) data towards nearby hot, white dwarfs
  (WDs). The advantages of using STIS for this study are: (1) The high
  velocity resolution of STIS in the UV ( ~ 2 km s<SUP>-1</SUP> in the
  E140H and E230H modes) allows the velocity structure in the sightline
  to be resolved and reliable component-to-component variations can be
  studied (2) WDs provide a strong, smooth UV continuum against which
  other diagnostic interstellar absorption lines can be measured. The
  wider wavelength coverage ( ~ 200Å per setting) of STIS in the
  high-resolution E140H mode allows important interstellar lines such as N
  i, Si ii, O i and S ii to be measured in addition to D i and H i, at no
  extra cost in HST time (3) The superior echelle scatter and background
  corrections possible with the 2-dimensional STIS-MAMA detectors allow
  more accurate D/H determinations from WD spectra. In this poster, we
  present a status report of our project along with some recent results.

Title: NGC 346-12, a Rapidly Rotating O9.5V Star in the SMC: Test
    Case of Weak Winds
Authors: Lanz, T.; Bouret, J. -C.; Heap, S. R.; Hubeny, I.; Hillier,
   D. J.; Lennon, D. J.; Smith, L. J.; Evans, C. J.; Owocki, S. P.
Bibcode: 2000AAS...197.7811L
Altcode: 2000BAAS...32R1531L
  We have analyzed the UV and optical spectrum of the O9.5V Star, NGC
  346-12, using sophisticated, NLTE line-blanketed model atmospheres
  calculated with our code TLUSTY. The following stellar parameters
  were derived: T<SUB></SUB> eff=30,000 K, log g=3.5. An abundance
  analysis yields a metallicity, [Fe/H]=-1.0. The N/C abundance ratio
  is 25 times the solar ratio, indicating that material processed
  through the CNO-cycle has been brought up to the surface. Assuming
  a distance modulus, (m-M)=18.9, for the SMC, we have derived the
  luminosity, radius, and mass of the star. We found, similarly to higher
  luminosity galactic stars, a discrepancy between the mass derived
  from the spectroscopic analysis and from stellar evolution theory. We
  conclude that it is very likely that NGC 346-12 is a fast rotator,
  whose evolution has been affected by rotation. Furthermore, the wind
  of NGC 346-12 appears abnormal: while the C IV resonance lines do not
  reveal any indication of a wind, a weak P-Cygni profile is observed
  in N 5 1240. Various possible explanations for the low inferred ion
  density in the stellar wind, including an enhanced degree of wind
  ionization associated with ion frictional heating, or ion runaway
  due to frictional decoupling from the hydrogen-helium bulk plasma,
  are examined. This work was supported through a NASA/NRC RA award and
  STScI grants (GO 7437, AR 7985).

Title: NLTE Model Atmosphere Analysis of Main-Sequence O Stars in
    NGC 346
Authors: Bouret, J. -C.; Heap, S. R.; Hubeny, I.; Lanz, T.; Hillier,
   D. J.; Lennon, D. J.; Smith, L. J.; Evans, C. J.
Bibcode: 2000AAS...197.7810B
Altcode: 2000BAAS...32.1531B
  To serve as spectral templates of young, low-metallicity populations,
  high-resolution, high-quality, ultraviolet (STIS) and optical spectra
  of several main-sequence O stars in NGC 346 have been obtained. Stellar
  parameters and abundance of light elements are derived from the optical
  spectrum using NLTE, line-blanketed, photospheric models calculated
  with TLUSTY. In addition, the UV spectrum is analyzed with the NLTE,
  line-blanketed wind model code, CMFGEN, to derive wind parameters
  (mass-loss rate, clumping properties, terminal velocity). Iron
  abundances, derived from fitting Fe 4 and Fe 5 lines with the two NLTE
  codes, compare favorably. We achieve good matches of the observed
  spectra, thus supporting our modeling work of spectra of starburst
  galaxies at high redshift. We finally discuss the dependence of the
  mass-loss rate in terms of metallicity and luminosity. This work
  was supported through a NASA/NRC RA award and STScI grants (GO 7437,
  AR 7985).

Title: Stellar Atmospheres: Early Type Stars
Authors: Hubeny, I.
Bibcode: 2000eaa..bookE1837H
Altcode:
  The topic `Stellar atmospheres of early type stars' has two individual
  ingredients, a (stellar) atmosphere, and an early type star. We shall
  specify these two terms in turn....

Title: Temporal Variations of the White Dwarf and Disk in OY Carinae
    Following the 1992 Superoutburst
Authors: Cheng, F. H.; Horne, Keith; Marsh, T. R.; Hubeny, Ivan;
   Sion, E. M.
Bibcode: 2000ApJ...542.1064C
Altcode:
  Hubble Space Telescope observations of the eclipsing dwarf nova
  OY Carinae after its 1992 April superoutburst are used to isolate
  ultraviolet spectra (1150-2500 Å at 9.2 Å FWHM resolution) of the
  white dwarf, the accretion disk, and the bright spot. The white dwarf
  spectra have a Stark-broadened photospheric Lyα absorption feature
  but are veiled by a forest of absorption features that we attribute to
  absorption by intervening disk material (a curtain). All the spectral
  fits required supersonic turbulence in the curtain material with
  Mach numbers of 6-8. All curtain temperatures were between 10,000 and
  11,000 K. There was a curtain temperature increase ~3 months after the
  superoutburst. We find that the white dwarf temperature changed from
  19,700 K just 27 days after the end of the superoutburst to 18,000 K
  roughly 3 months after the superoutburst; the exponential (e-folding)
  decay time of the white dwarf temperature was 66 days. We present
  evidence that the heating of the white dwarf was more extensive during
  the superoutburst than the normal outburst. The thermal response of the
  OY Car white dwarf to outburst heating is compared with WZ Sagittae,
  VW Hydri (the most similar dwarf nova to OY Car), and the cooling
  timescales of other dwarf novae after superoutburst. The measured
  cooling timescales of the five systems with superoutbursts appear to
  be shorter the longer the orbital period (accretion rate). Possible
  implications are discussed. There is evidence of a disk flux variation,
  independent of the effect of white dwarf cooling, which suggests a
  possible contradiction of the disk instability model. To establish
  this, however, data are required throughout a quiescent cycle. Based
  on observations with the NASA/ESA Hubble Space Telescope obtained
  at the Space Telescope Science Institute, which is operated by the
  Association of University Research in Astronomy, Inc., under NASA
  contract NAS 5-26555.

Title: Heavy element abundances in DA white dwarfs
Authors: Barstow, M. A.; Burleigh, M. R.; Bannister, N. P.; Holberg,
   J. B.; Hubeny, I.; Bruhweiler, F. C.; Napiwotzki, R.
Bibcode: 2000astro.ph.10448B
Altcode:
  We present a series of systematic abundance measurements for a group
  of hot DA white dwarfs in the temperature range 20,000-75,000K, based
  on far-UV spectroscopy with STIS on HST, IUE and FUSE. Using our latest
  heavy element blanketed non-LTE stellar atmosphere calculations we have
  addressed the heavy element abundance patterns for the hottest stars
  for the first time, showing that they are similar to objects like
  G191-B2B. The abundances observed in the cooler (&lt;50,000K) white
  dwarfs are something of a mystery. Some of the patterns (e.g. REJ1032)
  can be explained by self-consistent levitation-diffusion calculations
  but there is then a serious difficulty in understanding the appearance
  of the apparently pure H atmospheres. We also report the detection of
  photospheric HeII in the atmosphere of WD2218+706.

Title: Space Telescope Imaging Spectrograph Coronagraphic Observations
    of β Pictoris
Authors: Heap, Sara R.; Lindler, Don J.; Lanz, Thierry M.; Cornett,
   Robert H.; Hubeny, Ivan; Maran, S. P.; Woodgate, Bruce
Bibcode: 2000ApJ...539..435H
Altcode: 1999astro.ph.11363H
  We present new coronagraphic images of β Pictoris obtained with the
  Space Telescope Imaging Spectrograph (STIS) in 1997 September. The
  high-resolution images (0.1") clearly detect the circumstellar disk as
  close to the star as 0.75", corresponding to a projected radius of 15
  AU. The images define the warp in the disk with greater precision and
  at closer radii to β Pic than do previous observations. They show
  that the warp can be modeled by the projection of two components:
  the main disk and a fainter component, which is inclined to the main
  component by 4°-5° and extends only as far as ~4" from the star. We
  interpret the main component as arising primarily in the outer disk
  and the tilted component as defining the inner region of the disk. The
  observed properties of the warped inner disk are inconsistent with a
  driving force from stellar radiation. However, warping induced by the
  gravitational potential of one or more planets is consistent with the
  data. Using models of planet-warped disks constructed by Larwood &amp;
  Papaloizou, we derive possible masses of the perturbing object. Based
  on observations with the NASA/ESA Hubble Space Telescope, obtained
  at the Space Telescope Science Institute, which is operated by the
  Association of Universities for Research in Astronomy, Inc., under
  NASA contract NAS5-26555.

Title: The D/H Abundance Ratio in Local Interstellar Gas
Authors: Sahu, M. S.; Landsman, W.; Bruhweiler, F. C.; Linsky, J. L.;
   Hubeny, I.; Barstow, M.; Holberg, J.; Gull, T.; Bowers, C.; Lindler,
   D.; Lanz, T.; Feggans, K.
Bibcode: 2000AAS...196.2620S
Altcode: 2000BAAS...32..713S
  Does the D/H ratio vary within ~ 100 pc of the Sun? If it does, what
  is the range of these variations? Are the D/H variations correlated to
  any physical property of the absorbing cloud? To answer these questions
  we have begun a project to obtain high-precision D/H abundance ratios
  in the Local Interstellar Medium within ~ 100 pc (Sahu et al. 1999,
  ApJ 523, L159). For this purpose, we primarily use HST-Space Telescope
  Imaging Spectrograph (STIS) data towards nearby hot, white dwarfs
  (WDs). The advantages of using STIS for this study are: (1) The high
  velocity resolution of STIS in the UV ( ~ 2 km s<SUP>-1</SUP> in the
  E140H and E230H modes) allows the velocity structure in the sightline
  to be resolved and reliable component-to-component variations can be
  studied (2) WDs provide a strong, smooth UV continuum against which
  other diagnostic interstellar absorption lines can be measured. The
  wider wavelength coverage ( ~ 200 Angstroms per setting) of STIS in the
  high-resolution E140H mode allows important interstellar lines such as N
  i, Si ii, O i and S ii to be measured in addition to D i and H i, at no
  extra cost in HST time (3) The superior echelle scatter and background
  corrections possible with the 2-dimensional STIS-MAMA detectors allow
  more accurate D/H determinations from WD spectra. In this poster, we
  present a status report of our project along with some recent results.

Title: Analysis of the Spectrum of the z=2.73 Galaxy, MS1512-cB58:
    A Unified Model of the Stellar and Interstellar Contributions
Authors: Hubeny, I.; Heap, S. R.; Lanz, T. M.
Bibcode: 2000AAS...196.2914H
Altcode: 2000BAAS...32R.718H
  We perform a detailed analysis of the restframe far-UV spectrum of
  cB58 that was obtained by Pettini et al. (ApJ 528,96, 2000) using
  the KECK-I/LRIS. In the previous paper (AAS 195, 9.19), we modeled
  the spectrum of the galaxy and found that the observed spectrum is
  well described by a starburst model having a SMC-like metallicity
  and a constant star formation rate. Here, we extend the analysis to
  model the total spectrum that includes stellar as well as interstellar
  contributions. The latter is modeled using a newly developed program
  CLOUDSPEC that combines the photoionization program CLOUDY (Ferland,
  http://www.pa.uky.edu/ gary/cloudy) with our spectrum synthesis program
  SYNSPEC (Hubeny &amp; Lanz, http://tlusty.gsfc.nasa.gov). With the
  ionization structure of the interstellar medium given by CLOUDY,
  CLOUDSPEC solves the radiative transfer along the line-of-sight to
  the starburst and yields the profiles of the interstellar absorption
  lines. We show that such a ``unified'' model of the stellar +
  interstellar spectrum provides an excellent match to the observed
  spectrum of cB58.

Title: The discovery of photospheric nickel in the hot DO white
    dwarf REJ 0503-289
Authors: Barstow, M. A.; Dreizler, S.; Holberg, J. B.; Finley, D. S.;
   Werner, K.; Hubeny, I.; Sion, E. M.
Bibcode: 2000MNRAS.314..109B
Altcode:
  We present the first evidence for the direct detection of nickel
  in the photosphere of the hot DO white dwarf REJ 0503-289. While
  this element has been seen previously in the atmospheres of hot
  H-rich white dwarfs, this is one of the first similar discoveries
  in a He-rich object. Intriguingly, iron, which is observed to
  be more abundant than Ni in the hot DA stars, is not detected,
  the upper limit to its abundance (Fe/He=10<SUP>-6</SUP>) implying
  an Fe/Ni ratio a factor of 10 lower than seen in the H-rich objects
  (Ni/He=10<SUP>-5</SUP> for REJ 0503-289). The abundances of nickel and
  various other elements heavier than He were determined from Goddard High
  Resolution Spectrograph spectra. We used two completely independent
  sets of non-local thermodynamic equilibrium model atmospheres, which
  both provide the same results. This not only reduces the possibility of
  systematic errors in our analysis, but is also an important consistency
  check for both model atmosphere codes. We have also developed a more
  objective method of determining T<SUB>eff</SUB> and logg, from the He
  lines in the optical spectrum, in the form of a formal fitting of the
  line profiles to a grid of model spectra, an analogue of the standard
  procedure utilizing the Balmer lines in DA white dwarfs. This gives the
  assigned uncertainties in T<SUB>eff</SUB> and logg a firm statistical
  basis and allows us to demonstrate that inclusion of elements heavier
  than H, He and C in the spectral calculations, exclusively considered
  in most published optical analyses, yields a systematic downward shift
  in the measured value of T<SUB>eff</SUB>.

Title: STIS Observations of HE II Gunn-Peterson Absorption toward
    Q0302-003
Authors: Heap, Sara R.; Williger, Gerard M.; Smette, Alain; Hubeny,
   Ivan; Sahu, Meena S.; Jenkins, Edward B.; Tripp, Todd M.; Winkler,
   Jonathan N.
Bibcode: 2000ApJ...534...69H
Altcode:
  The ultraviolet spectrum (1145-1720 Å) of the distant quasar
  Q0302-003 (z=3.286) was observed at 1.8 Å resolution with the Space
  Telescope Imaging Spectrograph aboard the Hubble Space Telescope. A
  total integration time of 23,280 s was obtained. The spectrum clearly
  delineates the Gunn-Peterson He II absorption trough, produced by He II
  Lyα along the line of sight over the redshift range z=2.78-3.28. Its
  interpretation was facilitated by modeling based on Keck HIRES spectra
  of the H I Lyα forest (provided by A. Songaila and by M. Rauch and
  W. Sargent). We find that near the quasar, He II Lyα absorption
  is produced by discrete clouds, with no significant diffuse gas;
  this is attributed to a He II ``proximity effect'' in which the
  quasar fully ionizes He in the diffuse intergalactic medium, but
  not the He in denser clouds. By two different methods we calculate
  that the average He II Lyα opacity at z~3.15 is τ&gt;=4.8. In the
  Dobrzycki-Bechtold void in the H I Lyα forest near z=3.18, the average
  He II opacity τ=4.47<SUP>+0.48</SUP><SUB>-0.33</SUB>. Such large
  opacities require the presence of a diffuse gas component as well as
  a soft UV background spectrum, whose softness parameter, defined as
  the ratio of the photoionization rate in H I over the one in He II
  S≡Γ<SUP>J</SUP><SUB>HI</SUB>/ Γ<SUP>J</SUP><SUB>HeII</SUB>~=800,
  indicating a significant stellar contribution. At z=3.05, there is a
  distinct region of high He II Lyα transmission that most likely arises
  in a region where helium is doubly ionized by a discrete local source,
  quite possibly an AGN. At redshifts z&lt;2.87, the He II Lyα opacity
  detected by STIS, τ=1.88, is significantly lower than at z&gt;3. Such
  a reduction in opacity is consistent with Songaila's report that the
  hardness of the UV background spectrum increases rapidly from z=3 to
  z=2.9. Based on observations with the NASA/ESA Hubble Space Telescope,
  obtained at the Space Telescope Science Institute, which is operated
  by the Association of Universities for Research in Astronomy, Inc.,
  under NASA contract NAS5-26555.

Title: On the Age Estimation of LBDS 53W091
Authors: Yi, Sukyoung; Brown, Thomas M.; Heap, Sara; Hubeny, Ivan;
   Landsman, Wayne; Lanz, Thierry; Sweigart, Allen
Bibcode: 2000ApJ...533..670Y
Altcode: 1999astro.ph.11067Y
  The recent spectral analysis of LBDS 53W091 by Spinrad and his
  collaborators has suggested that this red galaxy at z=1.552 is at
  least 3.5 Gyr old. This imposes an important constraint on cosmology,
  suggesting that this galaxy formed at z&gt;~6.5, assuming recent
  estimates of cosmological parameters. While their analysis was heavily
  focused on the use of some UV spectral breaks as age indicators,
  we have performed χ<SUP>2</SUP> tests to the continuum of this
  galaxy using its UV spectrum and photometric data (R, J, H, and K:
  2000-9000 Å in rest frame). We have used the updated Yi models
  that are based on the Yale tracks. We find it extremely difficult to
  reproduce such large age estimates, under the assumption of the most
  probable input parameters. Using the same configuration as in Spinrad
  et al. (conventional solar abundance models), our analysis suggests
  an age of approximately 1.4-1.8 Gyr. We have improved our models over
  conventional ones by taking into account convective core overshoot in
  the stellar model calculations and realistic metallicity distributions
  in the galaxy population synthesis. Overshoot affects the visible
  continuum normalized to the UV and raises the photometry-based age
  estimates by 25%. The use of metallicity mixtures affects the whole
  spectrum and raises all continuum-based age estimates by up to a factor
  of 2. If the mean metallicity of the stars in this galaxy is assumed
  to be twice solar, the models including these two effects match the UV
  spectrum and photometric data of LBDS 53W091 near the age of 1.5-2.0
  Gyr. Our results cannot be easily reconciled with that of Spinrad et
  al. The discrepancy between Spinrad et al.'s age estimate (based on
  the Jimenez models) and ours originates from the large difference in
  the model integrated spectrum: the Jimenez models are much bluer than
  the Yi models and the Bruzual &amp; Charlot models. We propose to apply
  some viable tests to them for verification and search for the origin
  of the difference through a more thorough investigation. Considering
  the significance of the age estimates of distant galaxies as probes
  of cosmology, it would be an urgent task.

Title: Non-LTE Models and Theoretical Spectra of Accretion Disks in
    Active Galactic Nuclei. III. Integrated Spectra for Hydrogen-Helium
    Disks
Authors: Hubeny, Ivan; Agol, Eric; Blaes, Omer; Krolik, Julian H.
Bibcode: 2000ApJ...533..710H
Altcode: 1999astro.ph.11317H
  We have constructed a grid of non-LTE disk models for a wide range of
  values of black hole mass and mass accretion rate, for several values
  of the viscosity parameter α, and for two extreme values of the black
  hole spin: the maximum-rotation Kerr black hole, and the Schwarzschild
  (nonrotating) black hole. Our procedure calculates self-consistently
  the vertical structure of all disk annuli together with the radiation
  field, without any approximations imposed on the optical thickness
  of the disk, and without any ad hoc approximations to the behavior
  of the radiation intensity. The total spectrum of a disk is computed
  by summing the spectra of the individual annuli, taking into account
  the general relativistic transfer function. The grid covers nine
  values of the black hole mass between M=1/8×10<SUP>9</SUP> and
  32×10<SUP>9</SUP> M<SUB>solar</SUB> with a twofold increase of mass
  for each subsequent value; and eleven values of the mass accretion
  rate, each a power of 2 times 1 M<SUB>solar</SUB> yr<SUP>-1</SUP>. The
  highest value of the accretion rate corresponds to the total luminosity
  L/L<SUB>Edd</SUB>~0.3. We show the vertical structure of individual
  annuli within the set of accretion disk models, along with their local
  emergent flux, and discuss the internal physical self-consistency of the
  models. We then present the full disk-integrated spectra and discuss
  a number of observationally interesting properties of the models,
  such as optical/ultraviolet colors, the behavior of the hydrogen Lyman
  limit region, polarization, and the number of ionizing photons. Our
  calculations are far from definitive in terms of the input physics,
  but generally we find that our models exhibit rather red optical/UV
  colors. Flux discontinuities in the region of the hydrogen Lyman limit
  are only present in cool, low-luminosity models, while hotter models
  exhibit blueshifted changes in spectral slope.

Title: The He II Gunn-Peterson Effect
Authors: Heap, Sara R.; Hubeny, Ivan; Smette, Alain; Williger, Gerard
Bibcode: 2000fist.conf..323H
Altcode:
  The UV background at a given redshift is representative of the starlight
  and QSO-light generated in earlier redshifts. It holds key information
  on the populations of stars and QSO's at high redshift. We have used
  observations of the He II Gunn-Peterson (G-P) effect along the line
  of sight to Q 0302-003 at z = 3.286 to constrain the spectral energy
  distribution of the UV background spectrum over the redshift range, z =
  2.78 - 3.28. Assuming that stars have softer spectra than do QSO's, we
  used the softness of the UV background to discriminate between these
  two possible classes of ionizing sources. We find that stars appear
  to be significant contributors to the UV background at z &gt; 3, but
  below z = 3, there is a hardening of the UV background suggestive of
  an increased contribution by QSO's.

Title: Model Atmospheres and Radiatively Driven Winds of Metal-Poor
    Stars
Authors: Hubeny, Ivan; Lanz, Thierry; Heap, Sally
Bibcode: 2000fist.conf..133H
Altcode:
  We present a grid of non-LTE metal-line-blanketed hydrostatic
  model atmospheres for various effective temperatures, surface
  gravities (luminosities), and metallicities. The metallicities range
  from an essentially metal-free, primordial composition to a solar
  composition. For each model, we calculate the exact radiation force and
  compare to gravity acceleration. We thus find for each metallicity,
  the maximum surface gravity as a function of effective temperature
  required for the radiation force to exceed gravity and thus to initiate
  a radiatively-driven wind.

Title: Commission 36: Theory of Stellar Atmospheres: (Theorie des
    Atmospheres Stellaires)
Authors: Pallavicini, R.; Dravins, D.; Barbuy, B.; Cram, L.; Hubeny,
   I.; Owocki, S.; Saio, H.; Sasselov, D.; Spite, M.; Stepien, K.;
   Wehrse, R.
Bibcode: 2000IAUTA..24..219P
Altcode:
  No abstract at ADS

Title: Properties of the z=2.73 Galaxy, MS1512-cB58
Authors: Heap, S. R.; Bouret, J. -C.; Hubeny, I.; Lanz, T. M.
Bibcode: 1999AAS...195.0919H
Altcode: 1999BAAS...31.1387H
  MS1512-cB58 is an z=2.73 galaxy whose apparent brightness is amplified
  by 30X due to gravitationally lensing. The restframe far-UV spectrum of
  cB58 that was obtained by Keck-I/LRIS is ``one of the best ultraviolet
  spectra of a starburst galaxy obtained at any redshift'' (Pettini et
  al. 1999, astro-ph/9908007). We have therefore analyzed and modelled the
  spectrum of this galaxy in order to obtain information about the stellar
  content of high-redshift galaxies. We find that our model spectrum is
  a near match to the observed spectrum of cB58 if we assume a constant
  rate of star formation, a SMC-like metallicity, and a Salpeter IMF
  extending up to 100 M<SUB>sun</SUB>. In our paper, we will present
  the details of the spectral synthesis (based on both observed and
  model spectra of OB stars), and we will investigate the reliability
  of current evolutionary tracks (based on single, non-rotating stars)
  for interpreting the spectra of star-forming galaxies.

Title: The Eclipsing Cataclysmic Variable V347 Puppis Revisited
Authors: Diaz, Marcos P.; Hubeny, Ivan
Bibcode: 1999ApJ...523..786D
Altcode:
  An observational study of the nova-like cataclysmic binary V347 Pup (LB
  1800) is presented. An analysis of optical and UV spectroscopy is made
  with the aim of defining the physical properties of the binary system
  and of the accretion disk. The study of the line profile behavior and
  the determination of the primary radial velocity are pursued using a
  variety of methods. We also present the detection of secondary spectral
  signatures that were used to derive the object's radial velocity
  curve. A tentative companion spectral classification and spectroscopic
  parallax are also given. A Doppler tomography study of Balmer and
  He II lines lead us to an estimate of the average surface brightness
  distribution of these lines in the accretion disk. Exploratory modeling
  of the accretion disk in V347 Pup and comparison with UV observations
  is carried on using the system parameters constrained by the radial
  velocity study.

Title: The D/H Ratio in Interstellar Gas toward G191-B2B
Authors: Sahu, M. S.; Landsman, W.; Bruhweiler, F. C.; Gull, T. R.;
   Bowers, C. A.; Lindler, D.; Feggans, K.; Barstow, M. A.; Hubeny, I.;
   Holberg, J. B.
Bibcode: 1999ApJ...523L.159S
Altcode: 1999astro.ph..8123S
  Recent analysis of Goddard High-Resolution Spectrograph (GHRS) echelle
  spectra suggests ~30% variations in the D/H abundance ratio along the
  line of sight to the nearby (69 pc) hot white dwarf (WD) G191-B2B
  (Vidal-Madjar et al.). Variations in the D/H ratio on such short
  length scales imply nonuniform production/destruction of deuterium
  and an inefficient mixing of gas in the local interstellar medium
  (LISM). We reinvestigate the question of the spatial variation
  of the local D/H abundance using both archival GHRS spectra and
  new echelle spectra of G191-B2B obtained with the Space Telescope
  Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. The
  STIS spectra were obtained in the high-resolution (E140H) mode
  and cover the wavelength region ranging from 1140 to 1700 Å. Our
  analysis uses stratified line-blanketed non-LTE model atmosphere
  calculations to determine the shape of the intrinsic WD Lyα profile
  and to estimate the WD photospheric contamination of the interstellar
  lines. Although three velocity components were reported previously
  toward G191-B2B, we deduce only two velocity components. The first
  component is at v<SUB>hel</SUB>~8.6 km s<SUP>-1</SUP>, and the second
  is at v<SUB>hel</SUB>~19.3 km s<SUP>-1</SUP>, which we identify
  with the local interstellar cloud (LIC). From the STIS data, we
  derive D/H = 1.60<SUP>+0.39</SUP><SUB>-0.27</SUB>×10<SUP>-5</SUP>
  for the LIC component and D/H&gt;1.26×10<SUP>-5</SUP> for the 8.6 km
  s<SUP>-1</SUP> component (uncertainties denote 2σ or 95% confidence
  limits). The derived D/H values in both components are consistent with
  (D/H)<SUB>LIC</SUB> = (1.5+/-0.1)×10<SUP>-5</SUP>, which was determined
  by Linsky in 1998. The STIS data provide no evidence for local or
  component-to-component variation in the D/H ratio. Our reanalysis of
  the GHRS data gives essentially the same results as Vidal-Madjar et al.,
  despite using two velocity components for the profile fitting (vs. three
  by Vidal-Madjar et al.) and a more physically realistic WD Lyα
  profile for G191-B2B. The GHRS data indicate a component-to-component
  variation as well as a variation of the D/H ratio in the LISM, neither
  of which are supported by the newer STIS data. The D I absorption
  in the GHRS spectrum is shallower than in the STIS spectrum. The
  most probable cause for this difference in the two data sets is the
  characterization of the background due to scattered light in the GHRS
  and STIS spectrographs. The D/H ratios derived are sensitive to the
  background-subtraction procedures employed. The two-dimensional MAMA
  detectors of STIS measure both the spatial and wavelength dependences
  of scattered light, allowing more accurate scattered-light corrections
  than was possible with GHRS. <P />Based on observations done with the
  NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science
  Institute, which is operated by the Association of Universities for
  Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555.

Title: Evidence for the stratification of Fe in the photosphere
    of G191-B2B
Authors: Barstow, M. A.; Hubeny, I.; Holberg, J. B.
Bibcode: 1999MNRAS.307..884B
Altcode: 1999astro.ph..6191B
  The presence of heavy elements in the atmospheres of the hottest H-rich
  DA white dwarfs has been the subject of considerable interest. While
  theoretical calculations can demonstrate that radiative forces,
  counteracting the effects of gravitational settling, can explain
  the detections of individual species, the predicted abundances
  do not accord well with observation. However, accurate abundance
  measurements can only be based on a thorough understanding of the
  physical structure of the white dwarf photospheres, which has proved
  elusive. Recently, the availability of new non-local thermodynamic
  equilibrium model atmospheres with improved atomic data has allowed
  self-consistent analysis of the extreme ultraviolet (EUV), far UV
  and optical spectra of the prototypical object G191-B2B. Even so, the
  predicted and observed stellar fluxes remain in serious disagreement at
  the shortest wavelengths (below ~190Å), while the inferred abundances
  remain largely unaltered. We show here that the complete spectrum of
  G191-B2B can be explained by a model atmosphere where Fe is stratified,
  with increasing abundance at greater depth. This abundance profile may
  explain the difficulties in matching observed photospheric abundances,
  usually obtained by analyses using homogeneous model atmospheres,
  to the detailed radiative levitation predictions, particularly as
  the latter are only strictly valid for regions deeper than where the
  EUV/far UV lines and continua are formed. Furthermore, the relative
  depletion of Fe in the outer layers of the atmosphere may be evidence
  for radiatively driven mass-loss in G191-B2B.

Title: RXTE, ROSAT, EUVE, IUE, and Optical Observations through the
    45 Day Supercycle of V1159 Orionis
Authors: Szkody, Paula; Linnell, A.; Honeycutt, Kent; Robertson, Jeff;
   Silber, Andrew; Hoard, D. W.; Pastwick, L.; Desai, V.; Hubeny, Ivan;
   Cannizzo, John; Liller, William; Zissell, Ronald; Walker, Gary
Bibcode: 1999ApJ...521..362S
Altcode:
  A complete 45 day supercycle of the cataclysmic variable V1159
  Ori comprising a superoutburst and eight normal outbursts was
  observed. Coverage included ground-based optical observations as well as
  observations with RXTE for 38 days, ROSAT for 34 days, IUE for 27 days,
  and Extreme Ultraviolet Explorer (EUVE) for 10 days. The resulting light
  curves reveal that the optical and UV light variations are inversely
  correlated with the RXTE and ROSAT fluxes, with the largest change in
  intensity occurring in the ROSAT bandpass. There is no evidence for a
  strong EUV/soft X-ray component during outburst. An outflowing wind
  is evident from the C IV line profile during each brief outburst as
  well as the superoutburst. The transitions from outburst states of the
  disk to quiescent states take place on timescales of hours. Accretion
  disk models can fit the UV line and continuum energy distributions
  near outburst only if the disk radial temperature profile is modified
  from the standard case to produce a hotter distribution in the outer
  annuli. The high mass transfer rate, the hot disk distribution, and
  the similarity of outbursts and superoutbursts argue for outside-in
  outbursts in this system.

Title: Opacities along the line of sight to and in the atmosphere
    of the white dwarf in the close detached DAO+dM binary <ASTROBJ>RE
    J0720-318</ASTROBJ>
Authors: Dobbie, P. D.; Barstow, M. A.; Burleigh, M. R.; Hubeny, I.
Bibcode: 1999A&A...346..163D
Altcode: 1999astro.ph..5205D
  We present the results from a multi-wavelength study of the mixed H+He
  composition DAO white dwarf <ASTROBJ>RE J0720-318</ASTROBJ>. A detailed
  analysis of UV and EUV spectroscopic data with state-of-the-art non-LTE
  photospheric models demonstrates that the observed opacity to EUV
  radiation probably results from a more complex structure than a simple
  H+He, chemically layered atmosphere. Instead, EUV photometry and phase
  resolved EUV spectroscopy indicate a likely spatial non-uniformity in
  the surface distribution of helium, which is consistent with a model
  in which material is accreted from the wind of the dM secondary. The
  rotational modulation of the spatially inhomogeneous EUV opacity
  allows us to estimate the rotation period of the white dwarf (0.463 +/-
  0.004 days). We have also reviewed two plausible origins proposed by
  Burleigh et al. (\cite{burleigh97}) and Dupuis et al. (\cite{dupuis97a})
  to account for the unusual N(HI)/N(HeI) ~ 1 along this line of sight. We
  conclude that it is probably due to the presence of a cloud of ionized
  gas along this line of sight, rather than a circumbinary disk. The
  cloud, residing between 123-170 pc distant in the direction of the
  CMa ISM tunnel, may be ~&gt; 40 pc in length.

Title: Far-Ultraviolet Space Telescope Imaging Spectrograph Spectra
    of the White Dwarf REJ 1032+532. II. Stellar Spectrum
Authors: Holberg, J. B.; Barstow, M. A.; Bruhweiler, F. C.; Hubeny,
   I.; Green, E. M.
Bibcode: 1999ApJ...517..850H
Altcode:
  We discuss the Hubble Space Telescope Space Telescope Imaging
  Spectrograph UV echelle spectrum of the hot DA white dwarf REJ
  1032+532. The interstellar data from this spectrum are presented by
  Holberg and coworkers. In this paper we discuss a number of strong
  photospheric features due to C, N, and Si that are present in the
  REJ 1032+532 spectrum. While the inferred heavy element content of
  REJ 1032+532 roughly matches the predictions of radiative levitation
  for carbon and silicon, the observed nitrogen abundance greatly
  exceeds predictions by a factor of 50. The observed shapes of the N V
  lines provide the first evidence, at UV wavelengths, of heavy element
  stratification in a hot DA white dwarf. Homogeneous models are unable to
  reproduce the shape of the REJ 1032+532 N V lines, nor can they account
  for the relatively low degree of EUV opacity in the star. We present
  a simple stratified nitrogen model that resolves these problems. The
  high degree of stratification in REJ 1032+532 is the signature of
  ongoing mass loss in this star. The radial velocity of REJ 1032+532
  obtained with Space Telescope Imaging Spectrograph differs by 44 km
  s<SUP>-1</SUP> from that obtained from the Balmer H I lines with the
  Multiple Mirror Telescope. This suggests that REJ 1032+532 is likely
  a member of a binary system containing either a late M star or another
  white dwarf. <P />Based on observations with the NASA/ESA Hubble Space
  Telescope obtained at the Space Telescope Science Institute, which is
  operated by the Association of Universities for Research in Astronomy,
  Inc., under NASA contract NAS 5-26555. <P />Observations reported here
  have been obtained in part with the Multiple Mirror Telescope, a joint
  facility of the University of Arizona and Smithsonian Institution.

Title: Hot stellar population synthesis from the UV spectrum: the
    globular cluster M79 (NGC 1904)
Authors: Vink, Jorick S.; Heap, Sara R.; Sweigart, Allen V.; Lanz,
   Thierry; Hubeny, Ivan
Bibcode: 1999A&A...345..109V
Altcode: 1999astro.ph..3258V
  We have analyzed the far UV-spectrum of the globular cluster
  M79. We show that the nearly Gaussian mass distribution of zero-age
  horizontal-branch stars, as derived by Dixon et al. (1996), is able
  to reproduce the far-UV Hopkins Utraviolet Telescope (HUT) spectrum,
  if there is a luminous UV-bright star of about T_eff\ = 9,500 K
  within the HUT entrance slit, or, more likely, if the horizontal
  branch morphology becomes considerably redder in the core of M79, as
  observed in some other centrally condensed globular clusters. Agreement
  between the synthetic and observed far-UV spectra for M79 would also
  be improved if the surface abundances of the heavy elements in the hot
  horizontal-branch stars were enhanced by radiative diffusion. Contrary
  to Dixon et al. (1996) we do not need extremely low gravities to
  reproduce the width of Ly alpha .

Title: The D/H Ratio in Interstellar Gas towards G191-B2B from STIS
    Echelle Observations
Authors: Sahu, M. S.; Landsman, W. B.; Bruhweiler, F. C.; Gull, T. R.;
   Bowers, C. A.; Lindler, D.; Feggans, K.; Barstow, M. A.; Hubeny, I.;
   Holberg, J. B.
Bibcode: 1999AAS...194.7116S
Altcode: 1999BAAS...31..945S
  We present STIS echelle observations of interstellar D i and H i Lyα
  and N i (1199.5, 1200.2 and 1200.7 Angstroms), C ii 1334.5 Angstroms,
  C(*) ii 1335.7 Angstroms, O i 1302 Angstroms, Si ii (1190, 1193,
  1260, 1304 and 1526 Angstroms), Si iii 1206.5 Angstroms, Al ii 1670.8
  Angstroms, S ii 1259.5 Angstroms and Fe ii 1608.5 Angstroms in the line
  of sight to the nearby (69 pc) hot, white dwarf (WD) G191-B2B. Compared
  to the GHRS study of G191-B2B by Vidal-Madjar et al. 1998 (VM98),
  the STIS E140H spectra have a higher velocity resolution (3 km s(-1)
  ), better S/N (between 20 to 50) and broader wavelength coverage
  (1150 to 1700 Angstroms). We use the Barstow &amp; Hubeny stratified
  non-LTE model atmosphere calculations which include the effects of
  line-blanketing from more than 9x10(6) atomic transitions (mainly
  Ni and Fe), both to determine the NLTE shape of the stellar Lyalpha
  profile and to estimate the contamination of the interstellar lines
  by WD photospheric lines. The interstellar N i 1200.7 Angstroms, Si
  ii 1193 &amp; 1304 Angstroms and Fe ii lines show no contamination by
  WD photospheric lines and are given more weight in our analysis. VM98
  reported three components while we detect only two velocity components
  in all the interstellar species observed: one at ~ 8.5 km s(-1) and one
  at ~ 19.3 km s(-1) which we identify as the LIC component. Using the
  NLTE stellar Lyα profile and a total column density of N(H i) ~ 2 x
  10(18) cm(-2) for both components (consistent with EUVE observations),
  we derive confidence contours. We find the D/H ratio with 2sigma
  confidence limits to lie within 1.77+/-0.2x10(-5) . This value is
  consistent with the value of (D/H)<SUB>LIC</SUB> = 1.6+/-0.1x10(-5)
  determined towards Capella (Linsky et al. 1995). The STIS data provide
  no evidence for local or cloud-to-cloud variation in the D/H ratio as
  suggested by VM98. Re-analysis of the GHRS data and comparison to the
  STIS data is in progress.

Title: Detailed non-LTE Analysis of the High-S/N STIS Spectrum of
    the Hot Subdwarf, BD+28{(deg}4211)
Authors: Hubeny, I.; Lanz, T.; Haas, S.; Heap, S. R.; Lindler, D. J.;
   Kaiser, M. E.
Bibcode: 1999AAS...194.6702H
Altcode: 1999BAAS...31..930H
  During the course of commissioning the Space Telescope Imaging
  Spectrograph (STIS), observations were obtained to demonstrate the
  feasibility of achieving very high S/N spectra in the ultraviolet
  with the MAMA detectors. The hot subdwarf, BD+28{(deg}4211) , was
  selected as the test case. The two series of FP-SPLIT observations
  (E140M and E230M) have been shown to provide spectra with S/N=370 per
  resolution element in both the far-UV and near-UV. The observations
  were reduced by an iterative procedure that uses models of all relevant
  scatter sources including echelle scatter, MAMA detector halo and OTA
  scatter. We have performed a detailed analysis of the spectrum, using
  sophisticated non-LTE model atmospheres including several million
  metal lines in non-LTE. First, we derive basic parameters of this
  star (effective temperature, surface gravity, chemical composition)
  and compare to earlier results. We present a detailed comparison of
  predicted and observed spectra in order to provide a benchmark for
  future detailed spectroscopic studies of hot compact objects. Finally,
  we present a preliminary analysis of the effects of elemental abundance
  stratification on the selected line profiles with the aim of studying
  the detectability of non-homogeneous abundance patterns.

Title: Synthetic spectra of young starbursts: exploring the
    metallicity dependence
Authors: de Koter, A.; Heap, S. R.; Hillier, D. J.; Hubeny, I.
Bibcode: 1999IAUS..193..485D
Altcode:
  No abstract at ADS

Title: Evidence for the stratification of Fe in the photosphere of
    G 191-B2B
Authors: Barstow, M. A.; Hubeny, I.; Holberg, J. B.
Bibcode: 1999ASPC..169..479B
Altcode: 1999ewwd.conf..479B
  No abstract at ADS

Title: Dating intermediate-age populations with main-sequence A and
    F-type stars
Authors: Lanz, T.; Heap, S.; Brown, T. M.; Hubeny, I.; Yi, S.
Bibcode: 1999ASPC..192..106L
Altcode: 1999sdsg.conf..106L
  No abstract at ADS

Title: On the Age Estimation of High Redshift Galaxies
Authors: Yi, S.; Brown, T. M.; Heap, S.; Hubeny, I.; Landsman, W.;
   Lanz, T.; Sweigart, A.
Bibcode: 1999ASPC..192..126Y
Altcode: 1999sdsg.conf..126Y
  No abstract at ADS

Title: On the Age Estimation of LBDS 53W091
Authors: Yi, S.; Brown, T.; Heap, S.; Hubeny, I.; Landsman, W.; Lanz,
   T.; Sweigart, A.
Bibcode: 1999ASPC..193..185Y
Altcode: 1999hrug.conf..185Y
  No abstract at ADS

Title: Mid-UV Spectroscopic Dating of LBDS 53W091
Authors: Heap, S. R.; Lanz, T. M.; Brown, T.; Hubeny, I.
Bibcode: 1999ASPC..193..167H
Altcode: 1999hrug.conf..167H
  No abstract at ADS

Title: Non-LTE model atmospheres of hot DA white dwarfs
Authors: Hubeny, I.; Barstow, M. A.; Lanz, T.; Holberg, J. B.
Bibcode: 1999ASPC..169..445H
Altcode: 1999ewwd.conf..445H
  No abstract at ADS

Title: Spectrophotometric Dating of Stars and Galaxies
Authors: Hubeny, Ivan; Heap, Sally; Cornett, Robert
Bibcode: 1999ASPC..192.....H
Altcode: 1999sdsg.conf.....H
  No abstract at ADS

Title: New Light Synthesis and Spectrum Synthesis Constraints on a
    Model for β Lyrae
Authors: Linnell, A. P.; Hubeny, I.; Harmanec, P.
Bibcode: 1998ApJ...509..379L
Altcode:
  A suite of programs that calculates both synthetic light curves and
  synthetic spectra for a binary system with an optically thick accretion
  disk has been applied for the first time to β Lyrae A. Our results
  demonstrate that the standard accretion disk model by Hubeny &amp;
  Plavec shows significant residuals from observations, both photometric
  and spectroscopic, and that no changes in adjustable parameters are
  able to remove the residuals. The basic problem is that the Hubeny
  &amp; Plavec model requires a small visible segment of the hot star
  at the center of the accretion disk and this requirement conflicts
  with the photometric evidence. As an alternative, we investigate
  standard accretion disk models in which the central star is hidden from
  view. We find that no model of this type can satisfy either the observed
  photometry or the IUE spectra. To resolve this impasse, we suggest the
  presence of a light-scattering region above the accretion disk faces,
  which scatters light from the central star into the line of sight and
  provides the high-T<SUB>eff</SUB> radiation component required by both
  the light curves and the observed spectra. This source of radiation is
  very likely related to the jets proposed by Harmanec et al. and Hoffman
  et al. We calculate the location of stream impact on the accretion disk
  rim. Observations show no detectable photometric signature of a rim
  bright spot. We suggest that the liberated kinetic energy is spread
  over a region sufficiently large and at a sufficient optical depth to
  suppress appearance of a bright spot. A slight asymmetry of primary
  minimum may indicate swelling of the accretion disk rim downstream
  from the stream impact point, with an attendant slight increase in
  obscuration of the background light sources.

Title: Age and Metallicity of F-type Stars
Authors: Lanz, T.; Heap, S. R.; Brown, T. M.; Hubeny, I.; Yi, S.
Bibcode: 1998AAS...193.0302L
Altcode: 1998BAAS...30.1246L
  The rest-frame ultraviolet spectrum of intermediate-age stellar
  populations (1 to few Gyr) is dominated by the UV flux of F-type
  stars at the main sequence turn-off. We have obtained high-resolution
  spectra of four well-studied F stars with STIS aboard HST to calibrate
  ultraviolet spectral features in terms of age and metallicity. The UV
  spectrum is mostly degenerate in terms of effective temperature and
  metallicity, but we found that two spectral indices, [2850/2770] and
  [2310/3040], allow a discrimination between these two parameters. The
  first index measures mainly the strength of Mg I 2852, while the second
  index is the mid-UV color. We find that the Mg I index is sensitive
  to the effective temperature, but insensitive to metallicity; the
  UV color is sensitive to both metallicity and T_eff. We discuss the
  importance of departures from LTE and chromospheric activity on these
  two spectral indices. We apply our results to estimate the time since
  the last major star formation episode in the early-type galaxy LBDS
  53W091 at redshift z=1.55.

Title: STIS Observations of He II Gunn-Peterson Absorption Toward
    Q0302-003
Authors: Heap, S. R.; Williger, G. M.; Smette, A.; Hubeny, I.; Sahu,
   M.; Jenkins, E. B.; Tripp, T. M.; Winkler, J. N.
Bibcode: 1998astro.ph.12429H
Altcode:
  The ultraviolet spectrum (1145--1720A) of the distant quasar Q
  0302--003 (z=3.286) was observed at 1.8A resolution with the Space
  Telescope Imaging Spectrograph aboard the Hubble Space Telescope. A
  total integration time of 23,280 s was obtained. The spectrum clearly
  delineates the Gunn-Peterson HeII absorption trough, produced by HeII
  Lya, along the line of sight over the redshift range z=2.78-3.28. Its
  interpretation was facilitated by modeling based on Keck HIRES spectra
  of the HI Lya forest (provided by A. Songaila and by M. Rauch and
  W. Sargent). We find that near the quasar HeII Lya absorption is
  produced by discrete clouds, with no significant diffuse gas; this
  is attributed to a HeII "proximity effect" in which the quasar fully
  ionizes He in the diffuse intergalactic medium, but not the He in denser
  clouds. By two different methods we calculate that the average HeII
  Lya opacity at z~3.15 is tau &gt;= 4.8. In the Dobrzycki-Bechtold
  void in the HI Lya forest near z=3.18, the average HeII opacity
  tau=4.47^{+0.48}_{-0.33}. Such large opacities require the presence of
  a diffuse gas component as well as a soft UV background spectrum, whose
  softness parameter, defined as the ratio of the photo-ionization rate
  in HI over the one in HeII, S=Gamma^J_HI/Gamma^J_HeII~=800, indicating a
  significant stellar contribution. At z=3.05, there is a distinct region
  of high HeII Lya transmission which most likely arises in a region where
  helium is doubly ionized by a discrete local source, quite possibly an
  AGN. At redshifts z&lt;2.87, the HeII Lya opacity detected by STIS,
  tau=1.88, is significantly lower than at z&gt;3. Such a reduction in
  opacity is consistent with Songaila's (1998) report that the hardness
  of the UV background spectrum increases rapidly from z=3 to z=2.9.

Title: Detailed Mid- and Far-Ultraviolet Model Spectra for Accretion
    Disks in Cataclysmic Binaries
Authors: Wade, Richard A.; Hubeny, Ivan
Bibcode: 1998ApJ...509..350W
Altcode: 1998astro.ph..6399W
  We present a large grid of computed far- and mid-ultraviolet spectra
  (850-2000 Å) of the integrated light from steady-state accretion
  disks in luminous cataclysmic variables. The spectra are tabulated at
  0.25 Å intervals with an adopted FWHM resolution of 1.0 Å, so they
  are suitable for use with observed spectra from a variety of modern
  space-borne observatories. Twenty-six different combinations of white
  dwarf mass M<SUB>wd</SUB> and mass accretion rate ṁ are considered,
  and spectra are presented for six different disk inclinations i. The
  disk models are computed self-consistently in the plane-parallel
  approximation, assuming LTE and vertical hydrostatic equilibrium, by
  solving simultaneously the radiative transfer, hydrostatic equilibrium,
  and energy balance equations. Irradiation from external sources is
  neglected. Local spectra of disk annuli are computed taking into account
  line transitions from elements 1-28 (H through Ni). Limb darkening as
  well as Doppler broadening and blending of lines are taken into account
  in computing the integrated disk spectra. The radiative properties
  of the models are discussed, including the dependence of ultraviolet
  fluxes and colors on M<SUB>wd</SUB>, ṁ, and i. The appearance of
  the disk spectra is illustrated, with regard to changes in the same
  three parameters. Finally, possible future improvements to the present
  models and spectra are discussed.

Title: An Empirical Isochrone of Very Massive Stars in R136a
Authors: de Koter, Alex; Heap, Sara R.; Hubeny, Ivan
Bibcode: 1998ApJ...509..879D
Altcode:
  We report on a detailed spectroscopic study of 12 very massive and
  luminous stars (M &gt;~ 35M<SUB>⊙</SUB>) in the core of the compact
  cluster R136a, near the center of the 30 Doradus complex. The three
  brightest stars of the cluster, R136a1, R136a2, and R136a3, have been
  investigated earlier by de Koter, Heap, &amp; Hubeny. Low-resolution
  spectra (&lt;200 km s<SUP>-1</SUP>) of the program stars were obtained
  with the GHRS and FOS spectrographs on the Hubble Space Telescope. These
  instruments covered the spectral range from 1200 to 1750 Å and from
  3200 to 6700 Å, respectively. Fundamental stellar parameters were
  obtained by fitting the observations by model spectra calculated with
  the unified ISA-WIND code of de Koter et al. supplemented by synthetic
  data calculated using the program TLUSTY. We find that the stars are
  almost exclusively of spectral type O3. They occupy only a relatively
  narrow range in effective temperatures between 40 and 46 kK. The
  reason for these similar T<SUB>eff</SUB>'s is that the isochrone of
  these very massive stars, which we determined to be at ~2 Myr, runs
  almost vertically in the H-R diagram. We present a quantitative method
  of determining the effective temperature of O3-type stars based on the
  strength of the O V λ1371 line. Present-day evolutionary calculations
  by Meynet et al. imply that the program stars have initial masses in the
  range of M<SUB>i</SUB> ~ 37-76 M<SUB>⊙</SUB>. The observed mass-loss
  rates are up to 3 (2) times higher than is assumed in these evolution
  tracks when adopting a metallicity Z = 0.004 (0.008) for the LMC. The
  high observed mass-loss rates imply that already at an age of ~2 Myr
  the most luminous of our program stars will have lost a significant
  fraction of their respective initial masses. For the least luminous
  stars investigated in this paper, the observed mass loss agrees with
  the prediction by the theory of radiation-driven winds (Kudritzki et
  al.). However, for increasing luminosity the observed mass loss becomes
  larger, reaching up to 3-4 times what is expected from the theory. Such
  an increasing discrepancy fits in with the results of de Koter et al.,
  where an observed overpredicted mass-loss ratio of up to 8 was reported
  for the brightest members of the R136a cluster, for which M<SUB>i</SUB>
  ~ 100 M<SUB>⊙</SUB> was found. The failure of the theory is also
  present when one compares observed over predicted wind momentum as
  a function of wind performance number. This strongly indicates that
  the shortcoming of the present state of the theory is connected to the
  neglect of effects of multiple photon momentum transfer. <P />Based on
  observations with the NASA/ESA Hubble Space Telescope obtained at the
  Space Telescope Science Institute, which is operated by AURA, Inc.,
  under NASA contract NAS 5-26555.

Title: Multidimensional, non-LTE Radiation Transport in Astrophysical
    Media
Authors: Hubeny, I.; van Noort, M.; Lanz, T.
Bibcode: 1998AAS...193.6918H
Altcode: 1998BAAS...30.1352H
  We present first results of our long-term program whose ultimate goal
  is to develop multidimensional, self-consistent, non-LTE radiation
  hydrodynamic and magnetohydrodynamic spectroscopic diagnostics of
  astronomical objects. As the first step, we have developed an efficient
  and robust 2-D and 3-D radiation transfer solver, based on the short
  characteristics method. We assume the source function either to be
  fully specified (i.e., the so-called formal solution of the transfer
  equation), or to be given in terms of the equivalent-two-level
  atom formalism. In the latter case, we have adopted the idea of
  the Accelerated Lambda Iteration technique to treat iteratively the
  non-LTE coupling of radiation and matter. We compare the efficiency and
  numerical accuracy of several variants of the short-characteristics
  scheme. Finally, we present some illustrative examples of radiative
  transfer for 2-D and 3-D media with the specified temperature, density,
  and velocity structure.

Title: STIS Spectroscopy of Q0302-003: The HeII Gunn Peterson Effect
Authors: Heap, S. R.; Hubeny, I.; Jenkins, E. B.; Sahu, M. S.; Smette,
   A.; Tripp, T. M.; Williger, G. M.; HST/STIS IDT
Bibcode: 1998AAS...193.0404H
Altcode: 1998BAAS...30.1248H
  We present a new far-UV spectrum of the z=3.29 QSO, Q0302-003, obtained
  by STIS. This spectrum traces redshifted HeII Lyman-alpha lambda 304
  absorption over a redshift range, z=2.8 - 3.28, at a resolution of
  Delta lambda =1 Angstroms. In agreement with previous observations by
  the FOC (Jakobsen et al. 1994) and the GHRS (Hogan et al. 1997), the
  STIS spectrum clearly shows the ``Gunn-Peterson absorption trough''
  formed by redshifted HeII Lyman-alpha . The STIS spectrum, however,
  also shows that the HeII opacity is not constant with redshift:
  there is a hole in the opacity at z=3.05 as well as numerous minor
  fluctuations in opacity at z&lt;3.05. We will describe the major
  features of the absorption trough and will compare the observed
  distribution of opacities with theoretical predictions.

Title: Non-LTE Models and Theoretical Spectra of Accretion Disks in
    Active Galactic Nuclei. II. Vertical Structure of the Disk
Authors: Hubeny, Ivan; Hubeny, Veronika
Bibcode: 1998ApJ...505..558H
Altcode: 1998astro.ph..4288H
  We have calculated several representative models of vertical structure
  of an accretion disk around a supermassive Kerr black hole. The
  interaction of radiation and matter is treated self-consistently,
  taking into account departures from LTE for calculating both the
  disk structure and the radiation field. The structural equations are
  described in detail, and various approximations are discussed. We have
  demonstrated that departures from LTE are very important for determining
  the disk structure, even at the midplane, as well as the emergent
  radiation, particularly for hot and electron-scattering-dominated
  disks. We have shown that at least for the disk parameters studied
  in this paper, non-LTE effects tend to reduce the value of the Lyman
  jump with respect to the LTE predictions, regardless whether LTE
  predicts an emission or absorption jump. We have studied the effects
  of various values of viscosity on the model structure and predicted
  spectral energy distribution. The viscosity is parameterized through a
  parameter α<SUB>0</SUB> that describes the vertically averaged viscous
  stress, two power-law exponents, ζ<SUB>0</SUB> and ζ<SUB>1</SUB>,
  and the division point m<SUB>d</SUB> between these two forms. The disk
  structure and emergent radiation is sensitive mainly to the values of
  α<SUB>0</SUB>, while the other parameters influence the disk structure
  to a much lesser extent. However, although the detailed shape of the
  predicted spectrum is sensitive to adopted value of α<SUB>0</SUB>,
  the overall appearance of the spectrum is quite similar.

Title: An alternative explanation of the EUV spectrum of the white
    dwarf G191-B2B invoking a stratified H+He envelope including heavier
    elements
Authors: Barstow, M. A.; Hubeny, I.
Bibcode: 1998MNRAS.299..379B
Altcode:
  Only recently has it been possible to find an effective temperature and
  composition for the hot DA white dwarf G191-B2B which can consistently
  match the optical, far-UV and EUV data simultaneously, by using new
  non-LTE model calculations that include the effects of line blanketing
  from more than 9 million (mainly Fe and Ni) transitions. However, to
  maintain agreement below the Heii 228-Angstroms Lyman limit requires
  the inclusion of additional Heii opacity in the form of photospheric,
  circumstellar or interstellar material. If photospheric, the homogeneous
  H+He structure adopted predicted a Heii 1640-Angstroms line strength
  well above the IUE detection limit, while an unusally high He ionization
  fraction was required in this particular line of sight if the material
  was in the local ISM. We show that, by considering the effects of a
  stratified H upon He photospheric structure within the heavy-element
  blanketed models, a lower interstellar Heii column density is obtained,
  leading to a more reasonable He ionization fraction for the G191-B2B
  line of sight. In addition, the absence of a Heii 1640-Angstroms
  feature in the far-UV data is consistent with the equivalent width
  predicted by the stratified model. However, while this alternative
  interpretation offers a better description of certain aspects of the
  G191-B2B optical-to-EUV spectra, a new problem is introduced, namely
  that the Heii Lyman lines are predicted to be stronger than can be
  comfortably accommodated by the observational data.

Title: The effect of photospheric heavy elements on the hot DA white
    dwarf temperature scale
Authors: Barstow, M. A.; Hubeny, I.; Holberg, J. B.
Bibcode: 1998MNRAS.299..520B
Altcode:
  Using the latest non-local thermodynamic equilibrium (non-LTE) synthetic
  spectra and stellar model calculations, we have evaluated the potential
  effect of the presence of heavy elements in the photospheres of hot
  H-rich DA white dwarfs. In particular, we have examined their influence
  on the effective temperature and surface gravity perceived from analysis
  of the Balmer line profiles. It is apparent that both the inclusion
  of non-LTE effects in the models and significant quantities of heavy
  elements act independently to lower the value of T_eff determined from a
  particular spectrum. Hence, the true effective temperatures of the heavy
  element-rich DA white dwarfs, currently estimated to be above 55000 K,
  are apparently lower than previously reported from pure-H LTE analyses,
  by some 4000-7000 K. We do not see any similar influence on measurements
  of log g. This work concentrates on a group of relatively bright
  well-studied objects, for which heavy element abundances are known. As
  a consequence of this, establishment of correct temperatures for all
  other hot white dwarfs will require a programme of far-UV spectroscopy
  in order to obtain the essential compositional information. Since only
  stars with effective temperatures lying notionally in the range from
  ~55000 to 70000 K (52000-62000 K when the non-LTE effects and heavy
  elements are taken into account) have been considered here, important
  questions remain regarding the magnitude of any similar effects in even
  hotter white dwarfs and pre-white dwarfs. The resulting implications
  for the plausibility of the evolutionary link between the main hot DA
  population and their proposed precursors, the H-rich central stars of
  planetary nebulae, need to be investigated.

Title: HST spatially resolved spectra of the accretion disc and gas
    stream of the nova-like variable UX Ursae Majoris
Authors: Baptista, Raymundo; Horne, Keith; Wade, Richard A.; Hubeny,
   Ivan; Long, Knox S.; Rutten, Rene G. M.
Bibcode: 1998MNRAS.298.1079B
Altcode: 1998astro.ph..4002B
  Time-resolved eclipse spectroscopy of the nova-like variable UX UMa
  obtained with the HST/FOS on 1994 August and November is analysed
  with eclipse mapping techniques to produce spatially resolved spectra
  of its accretion disc and gas stream as a function of distance from
  the disc centre. The inner accretion disc is characterized by a blue
  continuum filled with absorption bands and lines, which cross over
  to emission with increasing disc radius, similar to that reported
  by Rutten et al. at optical wavelengths. The comparison of spatially
  resolved spectra at different azimuths reveals a significant asymmetry
  in the disc emission at ultraviolet (UV) wavelengths, with the disc
  side closest to the secondary star showing pronounced absorption by an
  `iron curtain' and a Balmer jump in absorption. These results suggest
  the existence of an absorbing ring of cold gas whose density and/or
  vertical scale increase with disc radius. The spectrum of the infalling
  gas stream is noticeably different from the disc spectrum at the same
  radius suggesting that gas overflows through the impact point at the
  disc rim and continues along the stream trajectory, producing distinct
  emission down to 0.1R_L1. The spectrum of the uneclipsed light shows
  prominent emission lines of Lyalpha, Nv lambda1241, Siiv lambda1400,
  Civ lambda1550, Heii lambda1640, and Mgii lambda2800, and a UV continuum
  rising towards longer wavelengths. The Balmer jump appears clearly
  in emission indicating that the uneclipsed light has an important
  contribution from optically thin gas. The lines and optically thin
  continuum emission are most probably emitted in a vertically extended
  disc chromosphere + wind. The radial temperature profiles of the
  continuum maps are well described by a steady-state disc model in the
  inner and intermediate disc regions (R&lt;=0.3R_L1). There is evidence
  of an increase in the mass accretion rate from August to November (from
  M^. = 10^-8.3 +/- 0.1 to 10^-8.1 +/- 0.1M/yr^-1), in accordance with the
  observed increase in brightness. Since the UXUMa disc seems to be in a
  high mass accretion, high-viscosity regime in both epochs, this result
  suggests that the mass transfer rate of UX UMa varies substantially
  (~= 50 per cent) on time-scales of a few months. It is suggested that
  the reason for the discrepancies between the prediction of the standard
  disc model and observations is not an inadequate treatment of radiative
  transfer in the disc atmosphere, but rather the presence of additional
  important sources of light in the system besides the accretion disc
  (e.g. optically thin continuum emission from the disc wind and possible
  absorption by circumstellar cool gas).

Title: A Grid of Non-LTE Models and Theoretical Spectra of AGN
    Accretion Disks
Authors: Hubeny, I.; Blaes, O.; Agol, E.
Bibcode: 1998AAS...192.3606H
Altcode: 1998BAAS...30..862H
  We present a grid of non-LTE models of the vertical structure and
  emergent spectra of accretion disks around supermassive Kerr black
  holes. For computing the disk structure, the interaction of radiation
  and matter is treated self-consistently, taking into account departures
  from LTE for calculating both the disk structure and the radiation
  field. The basic parameters of the system are the black hole mass,
  M, the mass accretion rate, dot {M}, the angular momentum (rotation)
  of the black hole (a/M), and the chemical composition of the disk. The
  viscosity is parameterized through a parameter alpha which describes the
  vertically-averaged viscous stress, two power-law exponents zeta_0 and
  zeta_1 , and the division point m_d between these two forms. The disk
  structure and emergent radiation is sensitive mainly to the values of
  alpha , while the other parameters influence the disk structure to a
  much lesser extent. We have constructed a grid of non-LTE disk models
  for M = 1, 2, 4, 8, 10, 16, and 32 (in units of 10(9) M_sun), and the
  mass accretion rates 1, 2, 4, 8, 10, 16 M_sun/yr, for all combinations
  of these parameters which yield the total luminosity below the Eddington
  limit. In the present study, we have considered only H-He models with
  a solar helium abundance. We have assumed the maximum stable rotation
  of the black hole, a/M=0.998, and alpha was set to 0.01. Each disk
  was divided into a set of 20 - 25 concentric annuli covering the
  region between radii 1.3 to 50 gravitational radii, R_g = G M/c(2)
  . These annuli provide all emergent UV and harder disk radiation, and
  most of its optical radiation. The disk structure (including general
  relativistic effects) was computed with the code TLUSDISK; the local
  spectra of the annuli by program SYNSPEC; and the integrated spectrum
  of the disk taking into account all general relativistic effects was
  done by program KERRTRANS (Agol 1997).

Title: Hubble Space Telescope Eclipse Observations of the Nova-like
    Cataclysmic Variable UX Ursae Majoris
Authors: Knigge, Christian; Long, Knox S.; Wade, Richard A.; Baptista,
   Raymundo; Horne, Keith; Hubeny, Ivan; Rutten, René G. M.
Bibcode: 1998ApJ...499..414K
Altcode: 1998astro.ph..1206K
  We present and analyze Hubble Space Telescope observations of the
  eclipsing nova-like cataclysmic variable UX UMa obtained with the
  Faint Object Spectrograph. Two eclipses each were observed with the
  G160L grating (covering the ultraviolet waveband) in 1994 August and
  with the PRISM (covering the near-ultraviolet to near-infrared) in
  November of the same year. The system was ~50% brighter in November
  than in August, which, if due to a change in the accretion rate,
  indicates a fairly substantial increase in Ṁ<SUB>acc</SUB> by
  &gt;~50%. The eclipse light curves are qualitatively consistent with
  the gradual occultation of an accretion disk with a radially decreasing
  temperature distribution. The light curves also exhibit asymmetries
  about mideclipse that are likely due to a bright spot at the disk
  edge. Bright-spot spectra have been constructed by differencing the
  mean spectra observed at pre- and posteclipse orbital phases. These
  difference spectra contain ultraviolet absorption lines and show
  the Balmer jump in emission. This suggests that part of the bright
  spot may be optically thin in the continuum and vertically extended
  enough to veil the inner disk and/or the outflow from UX UMa in some
  spectral lines. Model disk spectra constructed as ensembles of stellar
  atmospheres provide poor descriptions of the observed posteclipse
  spectra, despite the fact that UX UMa's light should be dominated
  by the disk at this time. Suitably scaled single temperature model
  stellar atmospheres with T<SUB>eff</SUB> ~= 12,500-14,500 K actually
  provide a better match to both the ultraviolet and optical posteclipse
  spectra. Evidently, great care must be taken in attempts to derive
  accretion rates from comparisons of disk models to observations. One
  way to reconcile disk models with the observed posteclipse spectra
  is to postulate the presence of a significant amount of optically
  thin material in the system. Such an optically thin component
  might be associated with the transition region (``chromosphere'')
  between the disk photosphere and the fast wind from the system, whose
  presence has been suggested by Knigge &amp; Drew. In any event, the
  wind/chromosphere is likely to be the region in which many, if not
  most, of the UV lines are formed. This is clear from the plethora of
  emission lines that appear in the mideclipse spectra, some of which
  appear as absorption features in spectra taken at out-of-eclipse
  orbital phases. <P />Based on observations with the NASA/ESA Hubble
  Space Telescope, obtained at the Space Telescope Science Institute,
  which is operated by the Association of Universities for Research in
  Astronomy, Inc., under NASA contract NAS 5-2655.

Title: Light Synthesis and Spectrum Synthesis Constraints on a Model
    for beta Lyrae
Authors: Linnell, A. P.; Hubeny, I.; Harmanec, P.
Bibcode: 1998AAS...192.2602L
Altcode: 1998BAAS...30..850L
  We have used the program suite BINSYN (Linnell &amp; Hubeny 1996)
  to simulate recent optical light curves (Harmanec et al. 1996), OAO2
  light curves, and IUE spectra of beta Lyrae. beta Lyrae A is a mass
  transfer system in which the mass donor is the component eclipsed at
  primary minimum (optical wavelengths). That component has a mass of
  about 2.9 M_⊙ (Harmanec &amp; Scholz 1993). The companion has a mass
  of about 13.1 M_⊙ and is embedded in a thick accretion disk. The
  only successful simulation of observed beta Lyrae light curves,
  particularly OAO2 UV light curves, has been by Wilson &amp; Lapasset
  (1981,WL). WL modeled the mass gainer as a greatly flattened oblate
  spheroid. A standard model accretion disk representation was developed
  by Hubeny &amp; Plavec (1981,HP). The continuum requires the presence
  of a high T_eff component which HP attribute to a small visible segment
  of the hot central star. HP point out that the WL model, which is not a
  standard accretion disk model, cannot represent the required high T_eff
  component, and so cannot be an acceptable model. The HP model leads to
  deep UV stellar eclipses of the visible segment of the hot central star;
  but the OAO2 data exclude this model. The OAO2 data require an accretion
  disk thick enough completely to hide the central star. Extensive tests
  with BINSYN show that no standard model accretion disk can represent the
  optical wavelength light curves, the OAO2 data, and the IUE spectra. The
  crux of the problem is an inability to provide the high T_eff source,
  required by both the UV light curves and the IUE spectra. To resolve
  this impasse, we propose the existence of a corona which scatters light
  from the otherwise hidden hot central star into the line of sight to the
  observer. We plan to develop a BINSYN addition to test this proposal.

Title: Continuum spectra of quasar accretion disk models
Authors: Agol, Eric; Hubeny, Ivan; Blaes, Omer
Bibcode: 1998AIPC..431..175A
Altcode: 1998apas.conf..175A; 1997astro.ph.12162A
  We have calculated the spectrum and polarization of a standard thin
  accretion disk with parameters appropriate for a bright quasar. This
  model improves upon previous work by including ultraviolet metal
  line opacities, assumed for now to be in LTE. Though not yet fully
  self-consistent, our calculations demonstrate that metal lines can
  change the spectral slope, reduce the polarization, and reduce the Lyman
  edge feature in accretion disk spectra. Some observational differences
  between quasar spectra and accretion disk models might be reconciled
  with the inclusion of metal lines.

Title: Model atmospheres and synthetic spectra of quiescent accretion
    discs
Authors: Still, Martin D.; Horne, Keith; Hubeny, Ivan
Bibcode: 1998AIPC..431..133S
Altcode: 1998apas.conf..133S
  We aim to employ a fully self-consistent atmosphere code to determine
  surface density, Σ, effective temperature, Teff, and microturbulence,
  Vturb, from emission line spectra of quiescent accretion discs. We
  have built a grid of solar-abundance, LTE, isothermal disc atmosphere
  models and investigate the sensitivity of the optical spectrum to Teff,
  Σ and Vturb. The results of fitting the grid to a synthetic quiescent
  disc spectrum and the spectrum of the dwarf nova SS Cyg are presented.

Title: Non-LTE models and theoretical spectra of accretion disks in
    Active Galactic Nuclei
Authors: Hubeny, Ivan; Hubeny, Veronika
Bibcode: 1998AIPC..431..171H
Altcode: 1998apas.conf..171H
  We present self-consistent models of the vertical structure and emergent
  spectrum of AGN accretion disks. The central object is assumed to be
  a supermassive Kerr black hole. We demonstrate that non-LTE effects
  and the effects of a self-consistent vertical structure of a disk
  play a very important role in determining the emergent radiation,
  and therefore should be taken into account. In particular, non-LTE
  models exhibit a largely diminished H I Lyman discontinuity, and strong
  emission in the He II Lyman discontinuity. Consequently, the number of
  ionizing photons in the He II Lyman continuum predicted by non-LTE disk
  models is by 1-2 orders of magnitude higher than that following from the
  black-body approximation. We have also shown that metal line opacities
  are very important in predicting emergent spectra from AGN disks.

Title: A Photometric and Spectrophotometric Study of MR Cygni
Authors: Linnell, A. P.; Etzel, P. B.; Hubeny, I.; Olson, E. C.
Bibcode: 1998ApJ...494..773L
Altcode:
  A self-consistent, physically accurate program suite has been used
  in an accurate simulation of new spectroscopy and photometry of MR
  Cygni. Analysis of both the spectroscopic and photometric data used
  spectrum synthesis techniques and a synthetic photometry augmentation of
  a light synthesis program package. The theoretical light curves closely
  fit the observational data. The same self-consistent parameters from
  the light synthesis solution produced synthetic spectra precisely
  fitting the observed spectra at all orbital phases. <P />The
  IRAF-reduced spectroscopy has produced an accurate double-lined
  radial velocity curve. The derived mass ratio differs greatly from
  photometric mass ratios in the literature. New UBV photometry closely
  replicates existing data and indicates photometric stability of the
  binary system. A synthetic spectrum fitted to IUE data established the
  primary component T<SUB>eff</SUB>. The light curve solution determined
  a single set of system parameters used to calculate U, B, and V light
  curves. We conclude that MR Cygni is a member of the relatively rare
  class of hot Algol systems defined by Popper. It is likely that mass
  transfer still is in progress, but there is no evidence, either from
  orbital period variation or from a bright spot on the mass gainer,
  for its existence. The lack of Hα emission in any of our spectra,
  including one at phase 0.063, suggests a small current rate of mass
  transfer. The fact that our computationally self-consistent procedure
  has successfully represented both the photometry and the spectroscopy
  for a binary system whose components are appreciably distorted
  demonstrates the overall power of the procedure.

Title: Assessing the sensitivity of atmosphere FITS to accretion
    disc spectra
Authors: Still, M. D.; Horne, K.; Hubeny, I.
Bibcode: 1998ASPC..137..552S
Altcode: 1998wsow.conf..552S
  No abstract at ADS

Title: HST Observations of the Fe II curtain in CVs
Authors: Catalán, M. S.; Horne, K.; Cheng, F. H.; Marsh, T. R.;
   Hubeny, I.
Bibcode: 1998ASPC..137..426C
Altcode: 1998wsow.conf..426C
  No abstract at ADS

Title: Non-LTE Line-Blanketed Model Atmospheres of O Stars
Authors: Hubeny, I.; Heap, S. R.; Lanz, T.
Bibcode: 1998ASPC..131..108H
Altcode: 1998phls.conf..108H
  No abstract at ADS

Title: Non-LTE line-blanketed model atmospheres of hot stars
Authors: Hubeny, I.
Bibcode: 1998ASPC..138..139H
Altcode: 1998stas.conf..139H
  No abstract at ADS

Title: Ultraviolet Spectral Dating of Stars and Galaxies
Authors: Heap, S. R.; Brown, T. M.; Hubeny, I.; Landsman, W.; Yi,
   S.; Fanelli, M.; Gardner, J. P.; Lanz, T.; Maran, S. P.; Sweigart,
   A.; Kaiser, M. E.; Linsky, J.; Timothy, J. G.; Lindler, D.; Beck,
   T.; Bohlin, R. C.; Clampin, M.; Grady, J.; Loiacono, J.; Krebs, C.
Bibcode: 1998ApJ...492L.131H
Altcode:
  An echelle spectrogram (R = 30,000) of the 2300-3100 Å region in
  the ultraviolet spectrum of the F8 V star 9 Comae is presented. The
  observation is used to calibrate features in the mid-ultraviolet spectra
  of similar stars according to age and metal content. In particular, the
  spectral break at 2640 Å is interpreted using the spectral synthesis
  code SYNSPEC. We use this feature to estimate the time since the last
  major star formation episode in the early-type galaxy LBDS 53W091 at
  redshift z=1.55, whose rest-frame mid-ultraviolet spectrum, observed
  with the Keck Telescope, is dominated by the flux from similar stars
  that are at or near the main-sequence turnoff in that system (Spinrad
  et al.). Our result, 1 Gyr if the flux-dominating stellar population
  has a metallicity twice solar, or 2 Gyr for a more plausible solar
  metallicity, is significantly lower than the previous estimate and
  thereby relaxes constraints on cosmological parameters that were implied
  by the earlier work. <P />Based on observations with the NASA/ESA Hubble
  Space Telescope, obtained at the Space Telescope Science Institute,
  which is operated by the Association of Universities for Research in
  Astronomy, Inc., under NASA contract NAS5-2655.

Title: HST synthetic spectral analysis of U GEM in early and late
quiescence: A heated white dwarf and accretion belt?
Authors: Cheng, F. H.; Sion, E. M.; Horne, Keith; Hubeny, I.; Huang,
   M.; Vrtilek, S. D.
Bibcode: 1997AJ....114.1165C
Altcode:
  We have re-examined two archival HST FOS G130H spectra of the prototype
  dwarf nova U Geminorum obtained during its quiescence 13 days and 70
  days after a wide outburst. Using synthetic spectral fitting with two
  flux-emitting components, a slowly rotating white dwarf photosphere,
  and a rapidly spinning accretion belt (V<SUB>rot</SUB> sin i=3200 km
  s<SUP>-1</SUP>) significantly improves the spectral fit but does not
  provide a unique solution. We found clear evidence for the cooling
  of the white dwarf, confirming earlier results, and evidence for the
  cooling of the accretion belt or gas in Keplerian motion as well. If
  an accretion belt is really present, then for the white dwarf and belt,
  respectively, 13 days post-outburst, we find T<SUB>wd</SUB>=37 000±400
  K and T<SUB>belt</SUB>=45 000 ±2500 K while at 70 days post outburst,
  we find T<SUB>wd</SUB>=33 500 ±700 K and T<SUB>belt</SUB>=37 500 ±4000
  K. These results are compared with our HST GHRS G160M observations
  obtained 13 days and 61 days after a narrow outburst of U Gem.

Title: Non-LTE Line-blanketed Model Atmospheres of Hot Stars. III. Hot
Subdwarfs: The sdO Star BD +75°325
Authors: Lanz, Thierry; Hubeny, Ivan; Heap, Sara R.
Bibcode: 1997ApJ...485..843L
Altcode:
  We have made a detailed comparison of results of spectroscopic analysis
  using three differents types of model atmospheres: classical non-LTE
  H-He models; approximate non-LTE line-blanketed models (with only
  a subset of Fe and Ni lines: those originating from transitions
  between levels with measured energies); and non-LTE fully blanketed
  models. The three models were applied to the sdO star BD +75°325,
  adopted as a test case. <P />We demonstrate that the effects of
  line blanketing are very important: the best fit of the observed H
  and He lines is achieved for T<SUB>eff</SUB> = 58,000 K when using
  H-He models, T<SUB>eff</SUB> = 55,000 K for approximate non-LTE
  line-blanketed models, and T<SUB>eff</SUB> = 52,000 K for fully
  blanketed non-LTE models. <P />Using the high-resolution Goddard
  High Resolution Spectrograph spectrum of BD +75°325 and our final
  fully blanketed model, we have derived reliable abundances of He, C,
  N, O, Si, Fe, and Ni. We find that BD +75°325 is an He-enriched star
  (He/H = 1 by number), whose surface exhibits CNO-cycle products, i.e.,
  N-rich (A<SUB>N</SUB> = 1.5 × 10<SUP>-3</SUP> by number, or 4.2 ×
  10<SUP>-3</SUP> by mass fraction), and C and O deficient (by factor of
  about 100 with respect to the solar value). We also find a significant
  surface depletion of silicon and an enhancement of iron and nickel. We
  argue that these anomalous abundances reflect some mixing with processed
  material from the core, with subsequent modification at the surface by
  diffusion processes. Finally, BD +75°325 possesses a weak wind. Using
  a simplified description of the wind, we have derived a preliminary
  value of the mass loss rate: Ṁ=1.5×10<SUP>-11</SUP> M<SUB>⊙</SUB>
  yr<SUP>-1</SUP>. <P />Based on observations with the ESA/NASA Hubble
  Space Telescope obtained at the Space Telescope Science Institute,
  which is operated by AURA, Inc., under NASA contract NAS 5-26555.

Title: Hubble Space Telescope Ultraviolet Spectroscopy of Two Hot
    White Dwarfs
Authors: Holberg, J. B.; Barstow, M. A.; Lanz, T.; Hubeny, I.
Bibcode: 1997ApJ...484..871H
Altcode:
  We have obtained Hubble Space Telescope high-dispersion spectroscopy of
  two hot white dwarfs using the Goddard High-Resolution Spectrograph. The
  stars were selected on the basis of EUV flux as examples of H-rich DA
  stars containing high and low levels of short-wavelength opacity. The
  high-opacity star, REJ 1614-085, possesses strong features due to C
  IV, Si IV, and N V. Carbon and silicon in this star are underabundant
  with respect to the predictions of radiative levitation; nitrogen,
  however, is superabundant. This is in sharp contrast to the apparently
  similar DA star GD 394, where silicon is in extreme overabundance. The
  low-opacity star PG 1057+719, as expected, shows no clear evidence of
  these or any other heavy ions. We find evidence of weak blueshifted
  components in the REJ 1614-085 C IV and Si IV lines, which may
  indicate the star is experiencing ongoing mass loss. <P />Based
  on observations with the NASA/ESA Hubble Space Telescope obtained
  at the Space Telescope Science Institute, which is operated by the
  Association of Universities for Research in Astronomy, Incorporated
  under NASA contract NAS 5-26555. <P />Observations reported here have
  been obtained in part with the Multiple Mirror Telescope, a joint
  facility of the University of Arizona and Smithsonian Institution.

Title: Non-LTE Models and Theoretical Spectra of Accretion Disks in
    Active Galactic Nuclei
Authors: Hubeny, Ivan; Hubeny, Veronika
Bibcode: 1997ApJ...484L..37H
Altcode: 1997astro.ph..5085H
  We present self-consistent models of the vertical structure and emergent
  spectrum of active galactic nucleus (AGN) accretion disks. The central
  object is assumed to be a supermassive Kerr black hole. We demonstrate
  that non-LTE (NLTE) effects and the effects of a self-consistent
  vertical structure of a disk play a very important role in determining
  the emergent radiation and therefore should be taken into account. In
  particular, NLTE models exhibit a largely diminished H I Lyman
  discontinuity when compared to LTE models, and the He II discontinuity
  appears strongly in emission for NLTE models. Consequently, the number
  of ionizing photons in the He II Lyman continuum predicted by NLTE disk
  models is 1-2 orders of magnitude higher than that following from the
  blackbody approximation. This prediction has important implications
  for ionization models of AGN broad-line regions and for models of
  the intergalactic radiation field and the ionization of helium in the
  intergalactic medium.

Title: Hubble Space Telescope GHRS Spectroscopy of U Geminorum during
    Two Outbursts
Authors: Sion, Edward M.; Cheng, Fuhua; Szkody, Paula; Huang, Min;
   Provencal, Judi; Sparks, Warren; Abbott, Brian; Hubeny, Ivan; Mattei,
   Janet; Shipman, Harry
Bibcode: 1997ApJ...483..907S
Altcode:
  We obtained Hubble Space Telescope Goddard High-Resolution Spectrograph
  medium-resolution (G160M grating) phase-resolved spectroscopic
  observations of the prototype dwarf nova U Geminorum during different
  stages of two different outbursts. The spectral wavelength ranges
  were centered on three different line regions: N V (1238 Å, 1242 Å),
  Si III (1300 Å), and He II (1640 Å). The spectrum corresponding to
  the early decline phase of outburst 1 is essentially featureless
  except for weak N V absorption and narrow interstellar lines,
  while the spectrum at the peak of outburst 2 reveals broad emission
  peaks separated by narrow central absorption. The double-peaked
  emission-line profile structure with low-velocity central absorption
  seen in the second outburst suggests a disk origin, but the emission
  velocity widths appear narrower than the widths of the optical disk
  emission features. We interpret the high-excitation emission lines,
  with central absorption below the continuum, to be due to photoionized
  material (coronal?) above the disk plane with the thickened outer disk
  absorbing the boundary layer or inner disk radiation. The possibility
  of a wind origin for the profiles is also discussed, as well as the
  possibility of an ejected optically thin shell. The N V absorption
  velocity versus orbital phase traces the motion of the white dwarf, but
  the He II absorption velocity appears to deviate from the white dwarf
  motion. We present the results of synthetic accretion disk spectral
  fitting to the data of both outbursts and derive accretion rates for the
  two outbursts of 6 × 10<SUP>-10</SUP> M<SUB>⊙</SUB> yr<SUP>-1</SUP>
  and 2 × 10<SUP>-9</SUP> M<SUB>⊙</SUB> yr<SUP>-1</SUP>. Implications
  are discussed. <P />Based on observations with the NASA/ESA Hubble
  Space Telescope, obtained at the Space Telescope Science Institute,
  which is operated by the Association of Universities for Research in
  Astronomy, Inc., under NASA contract NAS 5-26555.

Title: The Properties and Evolution of Very Massive Stars
Authors: Heap, S. R.; de Koter, A.; Hubeny, I.; Malumuth, E.
Bibcode: 1997AAS...190.2505H
Altcode: 1997BAAS...29..807H
  We present HST/FOS and GHRS spectra of 15 stars in the dense
  star cluster, R136a, in the Large Magellanic Cloud. These stars
  define an empirical isochrone for very massive stars (M &gt; 40
  M<SUB>sun</SUB>). We find that the cluster age is about 2.0 Myr, a time
  when the isochrone is very nearly vertical on the HR diagram. We have
  therefore used these stars: to refine the luminosity classification
  of early O-type stars to calibrate spectra of early O stars in terms
  of their fundamental parameters; to derive a new relation between
  the rate of mass-loss and the fundamental stellar parameters. The new
  mass-loss law is significantly different from previous prescriptions
  used by stellar evolutionary models. We therefore expect that it will
  have a significant impact on our knowledge of massive-star evolution.

Title: Testing the AGN Accretion Disk Paradigm by New Self-Consistent,
    Non-LTE Models
Authors: Hubeny, I.; Hubeny, V.
Bibcode: 1997AAS...190.3910H
Altcode: 1997BAAS...29..830H
  We present self-consistent models of the vertical structure and
  emergent spectrum of an accretion disk around a supermassive Kerr
  black hole. For the radial structure, we take into account general
  relativistic corrections after Riffert &amp; Herold (1996). For
  computing the vertical structure, the interaction of radiation and
  matter is treated self-consistently, taking into account departures from
  LTE for calculating both the disk structure and the radiation field. We
  demonstrate that non-LTE effects and the effects of self-consistent
  vertical structure of a disk play a very important role in determining
  the emergent radiation. In particular, non-LTE models exhibit a
  largely diminished H I Lyman discontinuity when compared to LTE
  models. Moreover, the He II discontinuity appears strongly in emission
  for non-LTE models. Consequently, the number of ionizing photons in
  the He II Lyman continuum increases significantly for non-LTE disk
  models. This prediction may be important for constraining models of
  the intergalactic radiation field and the ionization of helium in the
  intergalactic medium. We also compare the vertical structure models
  of a disk ring with the non-LTE stellar atmosphere models computed
  for the same effective temperature and as close surface gravity as
  possible. We found that athough the predicted flux roughly mimicks
  the results of self-consistent calculations, using stellar atmosphere
  models for approximating the AGN disk emergent radiation is risky
  because the predicted flux in the vicinity of the H I and He II Lyman
  discontinuities is very sensitive to the assumed value of the surface
  gravity.

Title: Dynamic Processes in Be Star Atmospheres. V. Helium Line
    Emissions from the Outer Atmosphere of λ Eridani
Authors: Smith, Myron A.; Cohen, D. H.; Hubeny, I.; Plett, K.; Basri,
   G.; Johns-Krull, C. M.; MacFarlane, J. J.; Hirata, R.
Bibcode: 1997ApJ...481..467S
Altcode:
  The He I lines of the mild B2e star λ Eri often exhibit rapid,
  small-amplitude emissions that can occur at random places in
  their photospheric lines, even when the star is in a ``nonemission
  state.'' New simultaneous observations of the triplet λ5876 and singlet
  λ6678 lines show that the emission ratio for these lines is near unity,
  contrary to the predictions of either non-LTE model atmospheres or
  nebular recombination theory. <P />Several He I emission events point to
  the formation of short-lived structures near the star's surface. On 1995
  September 12 the line λ6678 exhibited a strong (0.13I<SUB>cont</SUB>)
  emission lasting some 20 minutes. The rapid decay of this feature
  implies a density of &gt;=10<SUP>11.5</SUP> cm<SUP>-3</SUP> for an
  emitting plasma structure near the star. This value is consistent with
  density estimates for slabs which may be responsible for ephemeral
  ``dimples'' in this star's He I lines on other occasions. We argue that
  photospheric helium emissions during Hα-quiescent phases are caused
  by foreground material and ask what mechanism might produce these
  features against the stellar background. <P />To answer this question
  we have simulated He I line emission from model slabs having various
  properties and suspended over the star. We find that illumination by
  a source of extreme-ultraviolet (EUV) or X-ray flux depletes the He I
  column density so that it is difficult to form observable He I lines. A
  more interesting set of conditions occur for slabs with high densities
  (~10<SUP>12</SUP> cm<SUP>-3</SUP>) and moderately large optical
  thicknesses in optical He I lines. Under these modified assumptions
  modest amounts of emission can be reproduced in singlet and triplet
  lines, and in the observed ratio. The key to producing this emission is
  for the slab to feel its own Lyman continuum radiation. This condition
  causes λ584 and other resonance lines to partially depopulate the
  ground state and to overpopulate the first few excited levels, ensuring
  that the departure coefficients of relevant atomic levels approach
  common values. The second necessary ingredient is a high density,
  which tends to equalize the departure coefficients of excited levels
  through recombinations and through redistribution of electrons among the
  l-sublevels. The combination is a kind of ``Lyman-pumped recombination''
  because it relies on the Lyman continuum being marginally optically
  thick. Our results are consistent with studies of He I emission from
  planetary nebulae, symbiotic variables, and active galactic nuclei
  (AGNs), and may have a bearing on other ``detached atmospheres''
  problems as well. This study appears to be the first application of
  such a recombination mechanism to a quasi-photospheric setting.

Title: Evidence of a Thermonuclear Runaway and Proton Capture Material
    on a White Dwarf in a Dwarf Nova
Authors: Sion, E. M.; Cheng, F. H.; Sparks, W. M.; Szkody, P.; Huang,
   M.; Hubeny, I.
Bibcode: 1997AAS...190.2704S
Altcode: 1997BAAS...29Q.812S
  We present Hubble Space Telescope GHRS G160M spectra of the white dwarf
  in VW Hydri, exposed during quiescence, one month after the end of a
  normal dwarf nova outburst. Our spectra reveal strong photospheric Si
  II 1260 Angstroms, 1265 Angstroms absorption features, and a previously
  unidentified broad feature centered around 1250 Angstroms. This feature
  is due to a blend of phosphorus lines. From line-shift measurements
  we determine a gravitational redshift of 58 +/- 33 km s(-1) yielding a
  white dwarf mass, M = 0.86 (+0.18,-0.32) M_sun, white dwarf radius R =
  6.5 (+3.1,-1.5) x 10(8) cm, and gravity log g = 8.43 (+0.31,-0.54). Our
  best fitting synthetic spectra yield white dwarf effective temperature
  T = 22,000 K, a rotational velocity v sin i = 400 km s(-1) . The
  chemical abundances in number relative to solar are: C = 0.5, N =
  5.0, O = 2.0, Fe - 0.5, Si = 0.1, P = 900, and all other metals Z
  = 0.3. The abundance of phosphorus being 900 times solar, coupled
  with the elevated aluminum abundance reported by Sion and coworkers,
  suggest nucleosynthetic production of these odd-numbered nuclei from
  proton capture on the even-numbered nuclei during a CNO thermonuclear
  runaway (TNR) on the white dwarf. It is clear that the white dwarf has
  undergone a runaway sometime in the past, the first such evidence of
  a TNR in a dwarf nova. A TNR on a slowly accreting 0.86 M_sun white
  dwarf should produce a classical nova explosion. If our interpretation
  is correct, then we have found the first direct spectroscopic link
  between a dwarf nova and a classical nova by using the white dwarf
  surface chemical abundance. This is also the first direct evidence
  of proton capture-processed material in the atmosphere of a white
  dwarf. We acknowledge with gratitude the support of this work by NASA
  through grant GO6084.01-95A from the Space Telescope Science Institute,
  which is operated by the Association of Universities for Research in
  Astronomy, Inc., under NASA contract NAS5-26555.

Title: Evidence of a Thermonuclear Runaway and Proton-Capture Material
    on a White Dwarf in a Dwarf Nova
Authors: Sion, Edward M.; Cheng, F. H.; Sparks, Warren M.; Szkody,
   Paula; Huang, Min; Hubeny, Ivan
Bibcode: 1997ApJ...480L..17S
Altcode:
  We present Hubble Space Telescope Goddard High-Resolution Spectrograph
  G160M spectra of the white dwarf in VW Hydri, exposed during quiescence,
  1 month after the end of a normal dwarf nova outburst. Our spectra,
  covering the wavelength interval 1236-1272 Å, were obtained at
  orbital phase 0.06-1.60 they reveal strong photospheric Si II
  λλ1260, 1265 absorption features and a previously unidentified
  broad feature centered around 1250 Å. This feature is due to a
  blend of phosphorus lines. From line-shift measurements we determine
  a gravitational redshift of 58 +/- 33 km s<SUP>-1</SUP>, yielding a
  white dwarf mass M<SUB>wd</SUB> = 0.86<SUP>+0.18</SUP><SUB>-0.32</SUB>
  M<SUB>solar</SUB> (this is only the second gravitational redshift
  determined for a cataclysmic variable white dwarf), white dwarf radius
  R<SUB>wd</SUB> = 6.5<SUP>+3.1</SUP><SUB>-1.5</SUB> × 10<SUP>8</SUP>
  cm, and gravity log g = 8.43<SUP>+0.31</SUP><SUB>-0.54</SUB>. Our
  best-fitting synthetic spectra yield white dwarf effective temperature
  T<SUB>wd</SUB> = 22,000 K and a rotational velocity V<SUB>rot</SUB> =
  400 km s<SUP>-1</SUP>. The chemical abundances, in number relative to
  solar, are, for C, 0.5; N, 5.0; O, 2.0; Fe, 0.5; Si, 0.1; P, 900; and
  all other metals, 0.3. The abundance of phosphorus being 900 solar,
  coupled with the elevated aluminum abundance reported by Sion and
  coworkers, suggest nucleosynthetic production of these odd-numbered
  nuclei from proton capture on the even-numbered nuclei during a CNO
  thermonuclear runaway (TNR) on the white dwarf. It is clear that the
  white dwarf has undergone a runaway sometime in the past, the first
  such evidence of a TNR in a dwarf nova. A TNR on a slowly accreting
  0.86 M<SUB>solar</SUB> white dwarf should produce a classical nova
  explosion. If our interpretation is correct, then we have found the
  first direct spectroscopic link between a dwarf nova and a classical
  nova by using the white dwarf surface chemical abundance. This is
  also the first direct evidence of proton capture-processed material
  in the atmosphere of a white dwarf. Nova explosions on more numerous,
  lower mass C-O white dwarfs may therefore account for some fraction
  of the short-lived radionuclide <SUP>26</SUP>Al in the Galaxy. This
  nuclide is observed from its Galactic gamma-ray line emission and is
  postulated to have an important role in the heating of small bodies in
  the solar system. <P />Based on observations with the NASA/ESA Hubble
  Space Telescope, obtained at the Space Telescope Science Institute,
  which is operated by the Association of Universities for Research in
  Astronomy, Inc., under NASA contract NAS5-26555.

Title: On the Evolutionary Phase and Mass Loss of the Wolf-Rayet--like
    Stars in R136a
Authors: de Koter, Alex; Heap, Sara R.; Hubeny, Ivan
Bibcode: 1997ApJ...477..792D
Altcode:
  We report on a systematic study of the most massive stars, in which
  we analyzed the spectra of four very luminous stars in the Large
  Magellanic Cloud. The stars lie in the 30 Doradus complex, three of
  which are located in the core of the compact cluster, R136a (R136a1,
  R136a3, and R136a5), and the fourth (Melnick 42), located about 8"
  north of R136a. Low-resolution spectra (&lt;200 km s-1) of these four
  stars were obtained with the GHRS and FOS spectrographs on the Hubble
  Space Telescope. The GHRS spectra cover the spectral range from 1200
  to 1750 A, and the FOS spectra from 3200 to 6700 A. We derived the
  fundamental parameters of these stars by fitting the observations by
  model spectra calculated with the "ISA-WIND" code of de Koter et al. We
  find that all four stars are very hot (~45 kK), luminous, and rich in
  hydrogen. Their positions on the HR-diagram imply that they are stars
  with masses in the range 60--90 M⊙ that are 2 million years old
  at most, and hence, they are O-type main-sequence stars still in the
  core H-burning phase of evolution. Nevertheless, the spectra of two of
  the stars (R136a1, R136a3) mimic those of Wolf-Rayet stars in showing
  very strong He II emission lines. According to our calculations, this
  emission is a natural consequence of a very high mass-loss rate. We
  conjecture that the most massive stars in R136a---those with initial
  masses of ~100 M⊙ or more---are born as WR-like stars and that
  the high mass loss may perhaps be connected to the actual stellar
  formation process. Because the observed mass-loss rates are up to 3
  times higher than assumed by evolutionary models, the main-sequence
  and post--main-sequence tracks of these stars will be qualitatively
  different from current models. The mass-loss rate is 3.5--8 times
  that predicted by the analytical solutions for radiation-driven winds
  of Kudritzki et al. (1989). However, using sophisticated Monte Carlo
  calculations of radiative driving in unified model atmospheres, we show
  that---while we cannot say for sure what initiates the wind---radiation
  pressure is probably sufficient to accelerate the wind to its observed
  terminal velocity, if one accounts for the effects of multiple photon
  scattering in the dense winds of the investigated stars.

Title: O Stars in Transition. II. Fundamental Properties and
    Evolutionary Status of Ofpe/WN9 Stars from HST Ultraviolet
    Observations
Authors: Pasquali, Anna; Langer, Norbert; Schmutz, Werner; Leitherer,
   Claus; Nota, Antonella; Hubeny, Ivan; Moffat, Anthony F. J.
Bibcode: 1997ApJ...478..340P
Altcode:
  We present new HST/FOS ultraviolet spectroscopic observations of
  seven LMC Ofpe/WN9 stars. We find that Ofpe/WN9 stars have slow winds
  with terminal velocities of about 400 km s<SUP>-1</SUP> and high
  mass-loss rates of the order of 2-5 × 10<SUP>-5</SUP> M<SUB>⊙</SUB>
  yr<SUP>-1</SUP>. Ofpe/WN9 stellar temperatures and radii are in the
  range 30,000-39,000 K, and 19-39 R<SUB>⊙</SUB>, respectively. Stellar
  luminosities are between log (L/L<SUB>⊙</SUB>) = 5.6 and 6.3. <P
  />We study the Ofpe/WN9 stars winds and examine their evolutionary
  status. We find that Ofpe/WN9 stars are intermediate between O and W-R
  stars in terms of the wind momentum flux. We also find that the stellar
  properties and wind momentum of the Ofpe/WN9 sample place them in the
  evolutionary sequence: O --&gt; Of --&gt; H-rich WNL --&gt; Ofpe/WN9,
  for initial stellar masses less than ~100 M<SUB>⊙</SUB>. <P />In
  view of persisting discrepancies of standard massive star models with
  observations, we compute massive main-sequence models according to three
  different evolutionary scenarios. We find that both higher mass-loss
  rate and enhanced mixing between core and envelope are required in order
  to yield models compatible with the derived stellar and wind properties
  of Ofpe/WN9 stars. The emerging picture may be consistent with earlier
  evidence of Ofpe/WN9 stars being quiescent luminous blue variables
  (LBVs). This idea is further strengthened by the highly reduced surface
  H mass fractions of the Ofpe/WN9 stars. We derive X<SUB>s</SUB> = 0.5
  to 0.3, which still excludes Ofpe/WN9 stars from being core He-burning
  objects, but is almost identical to the X<SUB>s</SUB> values recently
  measured in LBVs. <P />Based on observations with the NASA/ESA Hubble
  Space Telescope, obtained at the Space Telescope Science Institute,
  which is operated by AURA for NASA under contract NAS5-26555.

Title: Interstellar and photospheric opacity from EUV spectroscopy
    of DA white dwarfs
Authors: Barstow, M. A.; Dobbie, P. D.; Holberg, J. B.; Hubeny, I.;
   Lanz, T.
Bibcode: 1997MNRAS.286...58B
Altcode:
  We present a detailed analysis of the extreme-ultraviolet (EUV)
  spectra of 13 hydrogen-rich DA white dwarfs, observed by the Extreme
  Ultraviolet Explorer (EUVE) satellite, paying attention to the
  possible sources of absorbing material along the lines of sight both
  in the local interstellar medium (ISM) and in the photospheres of the
  stars themselves. The range of interstellar column densities seen are
  consistent with our previous understanding of the local distribution of
  material. Absorption from interstellar Heii is found in the direction of
  five stars, allowing us to measure directly the He ionization fraction
  and estimate, indirectly, that of H. The weighted mean ionization
  fractions along these lines of sight are 0.27+/-0.04 and 0.35+/-0.1
  respectively. Where Heii is directly detected, the observed ionization
  fractions are not correlated with direction or with the volume/column
  density of material along the line of sight. Furthermore, the limits
  on the amount of Heii established in all other directions completely
  encompass the range of observed values. Indeed, all the data can be
  consistent with more or less constant He and H ionization fractions
  throughout the local ISM. It is clear that there is little photospheric
  opacity, from either He or heavier elements, in the majority of the
  stars we have studied. This poses further difficulties in explaining
  the observed division of white dwarfs into H- and He-rich groups,
  the temperature gap in the He-rich sequence and the detailed spectral
  evolution of the H-rich DA white dwarfs as they cool. A striking
  observational result is that our spectroscopic evidence indicates that
  radiative levitation effects are only important at temperatures above
  50000K, rather than the 40000K suggested by broad-band photometry. There
  is clearly an urgent need for further theoretical work on the mechanisms
  that determine the photospheric composition of white dwarf stars.

Title: NLTE Line Blanketed Model Atmospheres of A-Type Stars
Authors: Hubeny, I.; Lanz, T.
Bibcode: 1997IAUJD..16E.102H
Altcode:
  We present new non-LTE metal line-blanketed model atmospheres
  of A-type stars. We show that thanks to the recent progress in
  developing fast and robust numerical schemes, such as the hybrid
  complete linearization/accelerated lambda iteration method, one may
  now construct model atmospheres of unprecedented degree of complexity
  and realism. Other basic ingredient of the recent progress are the
  new atomic data calculations, like the Opacity and Iron Projects,
  which provide a substantial quantity of high-accuracy data. In this
  review we discuss the influence of the non-LTE approach, the influence
  of metal line blanketing, and the impact of new atomic data on model
  atmospheres and predicted spectra of A-type stars.

Title: HST synthetic spectral analysis of U Gem in early and late
quiescence: a heated white dwarf and accretion belt
Authors: Cheng, F. H.; Sion, E. M.; Horne, K.; Hubeny, I.; Huang,
   M.; Vrtilek, S. D.
Bibcode: 1997ASSL..214..359C
Altcode: 1997whdw.work..359C
  No abstract at ADS

Title: Heavy elements in white dwarf envelopes
Authors: Barstow, M. A.; Holberg, J. B.; Hubeny, I.; Lanz, T.
Bibcode: 1997ASSL..214..237B
Altcode: 1997whdw.work..237B
  No abstract at ADS

Title: Stellar Atmosphers Theory: an Introduction
Authors: Hubeny, I.
Bibcode: 1997LNP...497....1H
Altcode: 1997sato.conf....1H
  Fundamentals Concepts What Is a Stellar Atmosphere, and Why Do We
  Study It? Basic Structural Equations LTE Versus Non-LTE Radiative
  Transfer Equation Intensity of Radiation and Related Quantities
  Absorption and Emission Coefficient Phenomenological Derivation of
  the Transfer Equation Optical Depth and the Source Function Elementry
  Solutions Moments of the Transfer Equation Lambda Operator Diffusion
  Approximation Radiative Transfer with Constraints; Escape Probality
  Two-Level Atom Escape Probability Numerical Methods Formal Solution
  of the Transfer Equation Linear Coupling Problems Accelerated Lambda
  Iteration Non-linear Coupling Problems Model Atmospheres Definition and
  Terminology Basic Equations of Classical Stellar Atmospheres LTE-Grey
  Model: A Tool to Understand the Temperature Structure LTE and NLTE Model
  Atmospheres Line Blanketing Using Model Atmospheres to Analyse Observed
  Spectra A Scheme of Spectroscopic Diagnostics Spectrum Synthesis
  Spectrum Fitting Determination of Fundamental Stellar Parameters

Title: A Self-consistent Optical, Ultraviolet, and Extreme-Ultraviolet
    Model for the Spectrum of the Hot White Dwarf G191-B2B
Authors: Lanz, T.; Barstow, M. A.; Hubeny, I.; Holberg, J. B.
Bibcode: 1996ApJ...473.1089L
Altcode:
  The star G191-B2B is one of a number of hot DA white dwarfs whose
  atmospheres have been found to contain significant quantities of
  heavy elements, including C, N, 0, Si, Fe, and Ni. Several earlier
  studies have measured their abundances using IUE echelle data in
  conjunction with synthetic spectra derived from theoretical model
  atmosphere calculations of varying degrees of sophistication. However,
  predictions of the EUV spectrum based on these observations failed
  completely to match either its shape or absolute flux level. We
  present here the results of new non-LTE model calculations including
  the effects of line blanketing from more than 9 million (mainly Fe and
  Ni) transitions. For the first time, we are able to find an effective
  temperature and composition that can consistently match the optical, FUV
  and EUV data. However, to maintain this agreement below the He II λ228
  Lyman limit, it is necessary to incorporate additional He II opacity
  in the form of photo spheric, circumstellar or interstellar material.

Title: The Cooling White Dwarf in VW Hydri after Normal Outburst
and Superoutburst: HST Evidence of a Sustained Accretion Belt
Authors: Sion, Edward M.; Cheng, Fu-Hua; Huang, Min; Hubeny, Ivan;
   Szkody, Paula
Bibcode: 1996ApJ...471L..41S
Altcode:
  Hubble Faint Object Spectrograph (FOS) observations of VW Hyi one day
  after the end of a normal dwarf nova outburst reveal a heated white
  dwarf with deep, broad Ly alpha , narrow metallic absorption features,
  and evidence of a hotter Keplerian-broadened component manifested in
  quiescence as a broad continuum hump. Our best reduced chi 2 fit to
  the data reveals (1) a DAZQ white dwarf with Teff = 22,500 +/- 500 K,
  log g = 8, and photospheric abundances C = 0.5 solar, N = 5.0 solar,
  O = 2.0 solar, Si = 0.2 solar, Fe = 0.5 solar, with all other metals
  being 0.3 solar, and (2) a rapidly spinning accretion belt with Vrot =
  3350 km s-1, Tbelt = 26,000 +/- 1000 K, log g = 6.0, and a fractional
  belt area of approximately 11%. Our earlier FOS spectrum obtained 10
  days after superoutburst reveals a cooler DAZQ white dwarf (20,500 +/-
  1000 K), relatively lower metal abundances, and a smaller fractional
  area (3%) for the accretion belt. Thus, 1 day after a normal outburst,
  the white dwarf is ~2000 K hotter, the accretion belt fractional area
  is a factor of 3 greater, the accretion belt temperature appears to be
  cooler than at 10 days post-superoutburst, and the accreted atmosphere
  has relatively higher metal abundances. Finally, the accretion belt
  maintained during quiescence may provide a natural explanation for
  the 14 s soft X-ray oscillations, requires a deeper source of heating
  (compression and shear mixing), and implies a lower limit to the
  viscous spin-down timescale of 10 days.

Title: Ultraviolet Spectra and Limb Darkening of Accretion Disks
Authors: Diaz, M. P.; Wade, R. A.; Hubeny, I.
Bibcode: 1996RMxAC...4Q..95D
Altcode:
  No abstract at ADS

Title: A Spectrum Synthesis and Light Synthesis Program for Binary
    Stars with Optically Thick Accretion Disks
Authors: Linnell, A. P.; Hubeny, I.
Bibcode: 1996ApJ...471..958L
Altcode:
  We have completed a new program that calculates both synthetic spectra
  and synthetic light curves for binary systems that contain a standard
  model optically thick accretion disk. Our initial model is physically
  and geometrically simple. It is capable of substantial elaboration. By
  basing both synthetic light curves and synthetic spectra on a single
  self-consistent model, we anticipate useful tests of systems for which
  both types of data are available. Alternatively, explicit simulations
  now become possible for systems for which only light curves or only
  spectra are available.

Title: HST/GHRS Observations of the beta Pictoris
    System. II. Exploring the Potential for Tracking Comet-like Objects
    Orbiting the Star
Authors: Hubeny, Ivan; Heap, Sara R.
Bibcode: 1996ApJ...470.1144H
Altcode:
  We present a systematic study of the transient absorption features
  observed in the spectra of β Pictoris. We calculate detailed
  synthetic spectra of a star, which is partially obscured by a permanent
  circumstellar disk and by an absorbing body of a given size, position,
  radial velocity with respect to the star, and total column density. We
  show that because of the nonuniform surface brightness of the star,
  the strength of an absorption feature is an intricate function of both
  position and size. Consequently, one cannot determine the projected area
  of the body or its position from a single measurement only. However, by
  studying several closely spaced lines simultaneously, like those in the
  region of the Fe II UV1 multiplet at λ ≍2600 Å, one can determine
  both the position and size of the body. We present a preliminary
  analysis of Goddard High Resolution Spectrograph observations of β
  Pic in this region and show that while existing spectra do not have
  sufficient time coverage to allow us to track a single body during its
  transit across the stellar disk, our approach provides a robust means
  of tracking cometlike objects transiting the star and should be used to
  interpret future monitoring of β Pic and other stars showing similar
  variable absorption features. Conversely, the effect of body position
  is so great that it must be taken into account; absorption-line analyses
  based on techniques developed for interstellar lines should not be used.

Title: Observations of the Dwarf Nova VW Hydri in Quiescence with
    the Hopkins Ultraviolet Telescope
Authors: Long, Knox S.; Blair, William P.; Hubeny, Ivan; Raymond,
   John C.
Bibcode: 1996ApJ...466..964L
Altcode:
  The dwarf nova VW Hydri was in quiescence when it was observed in 1995
  March with the Hopkins Ultraviolet Telescope on the Astro-2 space
  shuttle mission. The far-UV (820-1840 Å) spectra are punctuated by
  broad Lyα and Lyβ absorption profiles and narrow absorption lines
  which can be identified with transitions expected in the atmosphere of
  a moderate-temperature white dwarf. There is no detectable emission
  shortward of 980 Å. The only emission line seen is C IV λλ1548,
  1551. If the emission from VW Hyi is due to a uniform-temperature
  white dwarf; then our spectra suggest that the temperature of the
  white dwarf was ∼17,000 K at the time of our observations and that
  abundances in the atmosphere were subsolar. Improved fits to the data
  are obtained using models in which the far-UV emission arises in part
  from a white dwarf with near-solar abundances and in part from the
  accretion disk. However, given the uncertainties in model spectra of
  metal-enriched atmospheres in this temperature range and our limited
  knowledge of quiescent accretion disks, higher S/N spectra are needed
  to unambiguously assess the disk contribution to the far-UV spectrum
  of VW Hyi in quiescence.

Title: Toward Resolving the ``Mass Discrepancy'' in O-Type Stars
Authors: Lanz, Thierry; de Koter, Alex; Hubeny, Ivan; Heap, Sara R.
Bibcode: 1996ApJ...465..359L
Altcode:
  We show that metal line blanketing has an important effect on the
  atmospheres of hot stars, and we argue that the omission of metal line
  blanketing in previous non-LTE model atmospheres of 0-type stars has led
  to underestimates of surface gravity and stellar mass. In addition to
  wind emission, metal line blanketing contributes to the solution of the
  long-standing discrepancy between spectroscopic and evolutionary masses
  for 0-type stars. <P />To support our argument, we calculated a series
  of non-LTE stellar atmospheres for 0 and Of-type stars. We compared the
  predicted profiles of hydrogen and helium lines produced by (1) a static
  plane- parallel H-He model, (2) a metal line-blanketed static model,
  and (3) an extended expanding model atmosphere. We find that simple
  H-He models produce stronger lines than do our metal line-blanketed
  models. Consequently, they lead to underestimated gravities. Wind
  emission is more effective in filling in the wings of H or He lines in
  the case of large mass-loss rates typical of extreme Of stars. These
  findings apply equally to young, massive 0-type stars and to highly
  evolved stars, i.e., central stars of planetary nebulae. The lower
  gravities derived from H-He models yield underestimated masses for
  young 0-type stars, and overestimated masses for highly evolved stars.

Title: The Accretion Disk (Belt?) During the Quiescence of VW Hydri
Authors: Huang, M.; Sion, E. M.; Hubeny, I.; Cheng, F. H.; Szkody, P.
Bibcode: 1996AJ....111.2386H
Altcode:
  We considered the contribution of an accretion disk to the UV spectrum
  of the dwarf nova (DN) VW Hydri during its quiescence, obtained with
  the Faint Object Spectrograph (FOS) on the Hubble Space Telescope
  (HST). Our analysis indicates that the UV emitting area of the disk is
  a ring of width 0.06 R<SUB>WD</SUB>, inclination angle i=60°, rotating
  with Keplerian velocity on the white dwarf surface of 3350 km/s. The
  other parameters of the ring are log g=6.0, T<SUB>eff</SUB>=28,000 K, C
  and Si enhanced to 20 and 15 times their solar abundances, respectively,
  and the abundance of all other heavy elements having solar values. The
  disk area outside this UV emitting region has a T<SUB>eff</SUB>
  much lower than 10,000 K. Our modelling does not rule out that the
  ring could actually be a belt on the white dwarf. For the central
  white dwarf, our analysis yields a T<SUB>eff</SUB>=22,000±1000 K,
  log g=8.0, with the abundance of all heavy elements 0.3 times their
  solar values. The disk contributes about 12% of the total far UV flux
  in the FOS far ultraviolet region.

Title: Photoionization resonances of SiII in stellar spectra.
Authors: Lanz, T.; Artru, M. -C.; Le Dourneuf, M.; Hubeny, I.
Bibcode: 1996A&A...309..218L
Altcode:
  We have studied the influence of the Si^+^ photoionization on stellar
  atmospheres. Recent calculations using the R-matrix code provide
  detailed cross-sections with autoionization resonances for the first
  50 energy levels of Si^+^. These photoionization cross-sections
  are included in the calculation of the far ultraviolet synthetic
  spectrum of A and late B-type stars. The opacity from the six lowest
  excited states of Si^+^ provides observable features in the emergent
  spectrum of a solar-composition A0 star. The photoionization from
  higher states of Si^+^ should be included when modeling hotter or
  silicon-rich stars. These new cross-sections increase dramatically
  the opacity in the far UV spectrum of Ap Si stars and allow to
  reproduce the most characteristic UV features of these stars, as
  illustrated by a comparison with IUE data for the hot Ap Si star HD
  34452. Broad features in its spectrum are definitely assigned to Si
  ii autoionization resonances, and the flux deficiency below 130nm is
  well matched with a predicted continuum edge near this wavelength. The
  successful stellar spectrum synthesis brings a strong support to
  the R-matrix photoionization calculations, which cannot otherwise be
  compared to laboratory data.

Title: Solving the mystery of the heavy-element opacity in the DA
    white dwarf GD 394.
Authors: Barstow, M. A.; Holberg, J. B.; Hubeny, I.; Lanz, T.;
   Bruhweiler, F. C.; Tweedy, R. W.
Bibcode: 1996MNRAS.279.1120B
Altcode:
  The white dwarf GD 394 is one of a very small number of bright hot DAs
  which have detectable quantities of highly ionized heavy elements in
  their spectra. Whether this material resides in the photosphere of GD
  394 or is in the form of a circumstellar shell has been the subject of
  much debate, with the large discrepancy between the published radial
  velocity of the star and the measured velocities of the Si III/IV
  lines having apparently settled the argument in favour of the latter
  idea. However, GD 394 is also the coolest DA white dwarf in the ROSAT
  sky survey showing convincing evidence for the presence of absorbing
  material which strongly suppresses the EUV continuum. This result has
  reopened the argument about the nature of the silicon lines. From a
  combined analysis of the IUE, HST and EUVE spectra, coupled with new
  measurements of the photospheric radial velocity from Hα data, the
  authors have established that the Si III and Si IV lines are indeed
  photospheric. Furthermore, other heavy elements must be present to
  account for the EUV opacity, but at levels below the thresholds for
  detecting absorption lines in either far-UV or EUV bands.

Title: EUVE Spectroscopy of beta Canis Majoris (B1 II--III) from
    500 Angstrom to 700 Angstrom
Authors: Cassinelli, J. P.; Cohen, D. H.; Macfarlane, J. J.; Drew,
   J. E.; Lynas-Gray, A. E.; Hubeny, I.; Vallerga, J. V.; Welsh, B. Y.;
   Hoare, M. G.
Bibcode: 1996ApJ...460..949C
Altcode:
  No abstract at ADS

Title: Ultraviolet Limb Darkening and Spectra for Accretion Disks
    in Cataclysmic Variables
Authors: Diaz, Marcos P.; Wade, Richard A.; Hubeny, Ivan
Bibcode: 1996ApJ...459..236D
Altcode:
  Limb darkening is an important effect, more so for flat objects such
  as accretion disks (ADs) than for stars, since no averaging over
  emergent angles occurs for disks. As with stars, limb darkening
  in ADs is especially important in the ultraviolet, and at a given
  wavelength it is more important for low- temperature atmospheres. We
  study the size of the limb-darkening effect in the ultraviolet (925 A
  to 1750 A) spectra of ADs in cataclysmic variables, using a grid of
  models and spectra of disk atmospheres. Radial emissivity (surface
  brightness) distributions in the ultraviolet are presented, along
  with a brief comparison of limb darkening in stars and disks. The
  changes in the absorption-line profiles in the model disk spectra as
  the disk inclination is varied, because of both limb darkening and
  kinematic broadening, are also discussed. Limb-darkening correction
  factors for the integrated disk brightness at 1448 A are derived for
  a representative set of disk parameters and orbital inclinations.

Title: EE Pegasi Revisited: A Spectrum Synthesis and New Light
    Synthesis Study
Authors: Linnell, A. P.; Hubeny, I.; Lacy, C. H. S.
Bibcode: 1996ApJ...459..721L
Altcode:
  A self-consistent physical model, described in an earlier paper
  by Linnell &amp; Hubeny, has permitted fits of synthetic spectra
  to observed spectra of EE Pegasi. The synthetic spectra determine
  abundances for iron, calcium, and silicon. The same model has been the
  basis of an optimized light synthesis solution of an accurate light
  curve by Ebbighausen. The solution, requiring use of a model atmospheres
  option to represent the component star radiative properties, agrees
  with the standard solution by Lacy &amp; Popper. The derived component
  parameters place them on an isochrone, determine a compositional Z,
  and are in accordance with evolution tracks by Schaller et al. The
  model is not restricted to systems with small distortion.

Title: Hubble Space Telescope/FOS Spectroscopy of VW Hydri in
    Superoutburst
Authors: Huang, M.; Sion, E. M.; Hubeny, I.; Cheng, F. H.; Szkody, P.
Bibcode: 1996ApJ...458..355H
Altcode:
  We present an analysis of two HST/FOS UV spectra of the SU UMa type
  dwarf nova, VW Hyi, obtained on 1993 October 24, ∼5 days after the
  optical rise of a superoutburst The absorption features in the first
  spectrum appear to consist of two components: a broad-winged component
  (with velocity width of 3000 km s<SUP>-1</SUP>) and a sharp core narrow
  component. This is the first time the narrow core is clearly resolved
  in super-outburst spectra of a dwarf nova system. The sharp core appears
  absent in the second spectrum obtained ∼10 minutes later. The broader
  component is mainly from the accretion disk. By comparing the spectra
  with a grid of LTE model accretion disk atmospheres constructed with
  TLUSTY, SYNSPEC, and DISKSYN, we present two possible disk fits to the
  observed spectra: a steady state disk with solar abundance and Mdot =
  3 × 10<SUP>9</SUP> M<SUB>sun</SUB> yr<SUP>-1</SUP> which can account
  for all the broad absorption features except for N V λ1240, and a model
  with a discontinuous T<SUB>eff</SUB>(r) distribution in which there is a
  contribution to the N V λ1240 absorption feature. We provide arguments
  supporting the possibility that the sharp cores are due to gas streams
  in the system. We also point out the far less likely possibility that
  the sharp cores form in a hot, high-gravity atmosphere. The synthetic
  fitting results may imply that the hot matter is accreted from the
  inner part of the disk onto the surface of the white dwarf through a
  highly inhomogeneous gas flow. We relate this discussion to our FOS
  detection of highly asymmetric inverse P Cygni profile structure in
  the narrow stellar components at C IV λ1550.

Title: Non-LTE spectroscopic analysis of the wind of the central
    star of NGC 6543
Authors: de Koter, A.; Hubeny, I.; Heap, S. R.; Lanz, T.
Bibcode: 1996ASPC...96..141D
Altcode: 1996hds..conf..141D
  No abstract at ADS

Title: Spectroscopic Constraints on the Helium Abundance in Globular
    Cluster Stars
Authors: Landsman, W. B.; Crotts, A. P. S.; Hubeny, I.; Lanz, T.;
   O'Connell, R. W.; Whitney, J.; Stecher, T. P.
Bibcode: 1996ASPC...99..199L
Altcode: 1996coab.proc..199L
  No abstract at ADS

Title: EUV Radiation from Hot Star Photoepheres: Theory Versus
    Observations
Authors: Hubeny, Ivan; Lanz, Thierry
Bibcode: 1996aeu..conf..381H
Altcode: 1996IAUCo.152..381H
  No abstract at ADS

Title: A quantitative study of limb darkening in accretion disks
Authors: Diaz, M. P.; Wade, R. A.; Hubeny, I.
Bibcode: 1996ASSL..208..123D
Altcode: 1996cvro.coll..123D; 1996IAUCo.158..123D
  No abstract at ADS

Title: Fundamental Properties of Ofpe/WN9 Stars from Ultraviolet
    HST Spectra<SUP>1</SUP>
Authors: Pasquali, A.; Schmutz, W.; Leitherer, C.; Nota, A.; Hubeny,
   I.; Langer, N.; Drissen, L.; Robert, C.
Bibcode: 1996swhs.conf..386P
Altcode:
  No abstract at ADS

Title: Model Spectra for Accretion Disks Truncated at the Inner Edge
Authors: Wade, Richard A.; Diaz, Marcos; Hubeny, Ivan
Bibcode: 1996aeu..conf..355W
Altcode: 1996IAUCo.152..355W
  No abstract at ADS

Title: Fully line-blanketed NLTE model atmospheres for hot
    hydrogen-deficient stars
Authors: Hubeny, I.; Lanz, T.
Bibcode: 1996ASPC...96..249H
Altcode: 1996hds..conf..249H
  No abstract at ADS

Title: The possible contribution from the accretion disk during the
    quiescence of VW HYI
Authors: Huang, M.; Sion, E. M.; Hubeny, I.; et al.
Bibcode: 1996ASSL..208..247H
Altcode: 1996cvro.coll..247H; 1996IAUCo.158..247H
  No abstract at ADS

Title: Spectrally resolved maps of optically thick accretion disks
Authors: Baptista, B.; Horne, K.; Hubeny, I.; et al.
Bibcode: 1996ASSL..208...17B
Altcode: 1996cvro.coll...17B; 1996IAUCo.158...17B
  No abstract at ADS

Title: The Composition and Structure of White Dwarf Atmospheres
    Revealed by Extreme Ultraviolet Spectroscopy
Authors: Barstow, Martin A.; Hubeny, Ivan; Lanz, Thierry; Holberg,
   Jay B.; Sion, Edward M.
Bibcode: 1996aeu..conf..203B
Altcode: 1996IAUCo.152..203B
  No abstract at ADS

Title: Atomic data for non-LTE model stellar atmospheres
Authors: Lanz, T.; Hubeny, I.; de Koter, A.
Bibcode: 1996PhST...65..144L
Altcode:
  We briefly review the state-of-the-art in non-LTE modeling of hot
  star atmospheres. During the last decade, the development of a
  new class of radiation transfer methods, based on the Accelerated
  Lambda Iteration method, have brought considerable progress in this
  field. Severe limitations of the size of model atoms used in non-LTE
  model atmospheres have been removed, so that realistic model atoms
  can now be considered. In recent years, the problem of non-LTE line
  blanketing, which aims to include the influence of thousands to millions
  of lines on the atmospheric structure, has been attacked, and first
  non-LTE line-blanketed models have been calculated. We illustrate
  the importance of non-LTE line blanketing with the example of a hot
  subdwarf, BD +75° 325. <P />As a consequence of these developments,
  there is a need for extensive radiative and collisional atomic databases
  to build non-LTE models. Recent projects, like the Opacity Project,
  provide a substantial quantity of the necessary data. We discuss the
  current needs of atomic data for the purpose of building reliable
  non-LTE line-blanketed model atmospheres. A critical evaluation of the
  quality of such extensive sets of atomic data is essential. Finally,
  we present a new, IDL-based, graphic tool intended to facilitate the
  manipulation of large amounts of data needed to build the realistic
  model atoms that we use.

Title: A Spectrum Synthesis and new Light Synthesis Study of EE Pegasi
Authors: Linnell, A. P.; Hubeny, I.; Lacy, C. H. S.
Bibcode: 1995AAS...187.6006L
Altcode: 1995BAAS...27.1372L
  EE Peg is among the binary systems with accurately known masses and
  radii (Andersen 1991, Astron. Astrophys. Rev., 3, 91). With component
  masses of 2.15 M_⊙, 1.33 M_⊙ and an orbital period of 2.63() d, this
  low distortion system is an excellent first test case for application
  of a new spectrum synthesis program for binary stars (Linnell &amp;
  Hubeny 1994, ApJ, 434, 738). The existing standard light curve solution
  is by Lacy &amp; Popper (1984, ApJ, 281, 268), analyzing an excellent
  B light curve by Ebbighausen. That paper also includes component mass
  determinations to 1%, based on spectra by Lacy. Our synthetic spectrum
  fits determine an iron abundance of log Fe=3.0x solar, and a calcium
  abundance of Ca=0.5x solar, consistent with the Am spectral type of the
  primary component. Calculation of a synthetic spectrum depends on prior
  knowledge of component dimensions and T_eff values. Consequently there
  is an interdependence with the light curve solution. Our light curve
  solution applied the light synthesis program by Linnell (1984, ApJS,
  54, 17). We found that use of the Planck Law to represent component
  radiative properties, a common procedure, produced a B-V component
  difference in strong disagreement with Popper's calibration of flux
  and T_eff for main sequence stars. A program modification permitted
  direct use of our synthetic spectrum results to represent the component
  radiative properties, with improved results. Since our program is
  applicable to systems of any distortion, successful analysis of EE
  Peg invites future discussion of distorted systems for which single
  values of T_eff and log g are inadequate.

Title: Partial Redistribution in Multilevel Atoms. I. Method and
    Application to the Solar Hydrogen Line Formation
Authors: Hubeny, I.; Lites, B. W.
Bibcode: 1995ApJ...455..376H
Altcode:
  We present a robust method for solution of multilevel non-LTE
  line transfer problems including the effects of partial frequency
  redistribution (PRD). This method allows the self-consistent solution
  for redistribution of scattered line photons simultaneously in multiple
  transitions of a model atom, including the effects of resonant Raman
  scattering ("cross-redistribution") among lines sharing common upper
  levels. The method is incorporated into the framework of the widely used
  non-LTE complete redistribution code MULTI. We have applied this method
  to the problem of transfer in hydrogen lines in a plane-parallel solar
  model atmosphere, including cross-redistribution between the Hα and
  Lβ, using general redistribution functions for the Lα and Lβ lines
  which are not restricted by the impact approximation. The convergence
  properties of this method are demonstrated to be comparable to that of
  the equivalent complete redistribution problem. In this solar model,
  PRD in the Lα line produces the dominant influence on the level
  populations. It changes considerably the populations of the excited
  states of hydrogen, as well as the proton number density, in the
  middle and upper chromosphere, owing to modification of the Lα wing
  radiation. <P />The population of the hydrogen ground state undergoes
  only modest changes, however. The influence of cross-redistribution
  and PRD in Lβ has a much smaller influence on the level populations
  but a considerable influence on the wing intensity of the Lβ line.

Title: Support for the Primordial Helium Abundance Derived from
    Observation of Globular Cluster Stars
Authors: Stecher, T. P.; Landsman, W.; Crotts, A. P. S.; Whitney,
   J.; O'Connell, R. W.; Lanz, T.; Hubeny, I.; Sweigart, A.
Bibcode: 1995AAS...187.8606S
Altcode: 1995BAAS...27.1414S
  The UIT on Astro-1 found nearly 2000 hot stars in the globular cluster
  Omega Centauri (Whitney et al. 1994, AJ, 108, 1350), of which 28 are at
  least 1 mag brighter than the horizontal branch (HB). We have obtained
  CTIO 4m and/or IUE low-dispersion spectra of eleven of the brightest
  of these stars. All seven stars observed at CTIO are radial velocity
  members of the clusters. Three of these stars have log Teff &gt; 60,000
  K and show only Balmer lines and He II lines. These stars, which appear
  to be in the post-asymptotic giant branch phase, are the hottest stars
  ever found in a globular cluster. The other four stars have log Teff ~
  20,000 K and show a B-type spectrum with numerous He I lines but none
  of He II. We have estimated the helium abundance by comparison with
  hydrogen-helium NLTE model stellar atmospheres. The He II lines in the
  hottest three stars in our sample appear to be best fit by models with
  a He/H ratio of about 0.1. This helium abundance should reflect the
  primordial helium abundance of the gas from which Omega Cen formed
  nearly 13 x 10(9) yr ago, except for the modest helium enrichment
  caused by the first dredge-up during the red giant branch phase. By
  analyzing these stars we have been able to derive a helium abundance
  for a globular cluster which is independent of the well-known R-method
  and which should provide an estimate of the helium abundance produced by
  the Big Bang. The four cooler stars in our sample show a quite different
  pattern of helium abundances. The three faintest of these stars have a
  substantially lower helium abundance which we attribute to the effects
  of diffusion during the preceding HB phase. These stars appear to
  have recently evolved off of the blue end of the HB. In contrast,
  the most luminous of these stars is very helium rich (He/H = 0.55),
  indicating that some UV-bright stars undergo interior mixing during
  their preceding AGB evolution.

Title: Accretion Disk Models for VOYAGER, HUT, and FUSE Far--UV
    Spectra
Authors: Wade, R. A.; Hubeny, I.
Bibcode: 1995AAS...187.7905W
Altcode: 1995BAAS...27.1397W
  Several past and future space missions have the capability
  to observe spectra of cataclysmic variables in the far--UV
  spectral region (from just short of the Lyman limit to longward
  of Lyman-alpha ). These include the VOYAGER Far--UV Spectrometers
  (FUVS), the Hopkins Ultraviolet Telescope (HUT; flew on ASTRO--1
  and ASTRO--2), and the planned FUSE mission. We present a model
  spectrum grid for axi\-symmetric, steady--state accretion disks
  in cataclysmic variable systems, where the accreting object is a
  white dwarf. The white dwarf mass and radius are varied on the grid,
  0.35 &lt;= M<SUB>wd</SUB>/M<SUB>sun</SUB> &lt;= 1.21 and 1.14 &gt;=
  R<SUB>wd</SUB>/(10(9) cm) &gt;= 0.38 respectively. The mass accretion
  rate is also varied, on the range -10.5 &lt;= log dM/dt &lt;= -8
  (M<SUB>sun</SUB> yr(-1) ). A standard Reynolds number description
  of the viscous dissipation is adopted. The local plane--parallel
  approximation is used, LTE is assumed, and irradiation of the
  disk or communication between different radial zones of the disk is
  ignored. Within these assumptions the vertical structure is calculated
  in a self--consistent manner to ensure both hydrostatic equilibrium
  and energy balance, using a restricted set of opacities. Ring and
  full--disk spectra are constructed from these models using a full
  line list, taking into account self--consistent limb darkening
  and Doppler shifts due to Keplerian orbital motion of the gas. The
  spectral region from 850 Angstroms to 1350 Angstroms is covered, and
  spectra at several inclinations are tabulated. The spectra will be
  made available electronically with a sampling interval and resolution
  sufficient to allow the study of FUVS and HUT spectra, and can be
  resampled for FUSE and other missions. The models serve as a benchmark
  against which more complicated models, perhaps including winds, can
  be compared. Representative spectra and some interesting trends are
  shown. Supported by NASA grants NAG5--2125 and NAGW--3171.

Title: The IUE MEGA Campaign: Wind Variability and Rotation in
    Early-Type Stars
Authors: Massa, D.; Fullerton, A. W.; Nichols, J. S.; Owocki, S. P.;
   Prinja, R. K.; St-Louis, N.; Willis, A. J.; Altner, B.; Bolton, C. T.;
   Cassinelli, J. P.; Cohen, D.; Cooper, R. G.; Feldmeier, A.; Gayley,
   K. G.; Harries, T.; Heap, S. R.; Henriksen, R. N.; Howarth, I. D.;
   Hubeny, I.; Kambe, E.; Kaper, L.; Koenigsberger, G.; Marchenko, S.;
   McCandliss, S. R.; Moffat, A. F. J.; Nugis, T.; Puls, J.; Robert, C.;
   Schulte-Ladbeck, R. E.; Smith, L. J.; Smith, M. A.; Waldron, W. L.;
   White, R. L.
Bibcode: 1995ApJ...452L..53M
Altcode:
  Wind variability in OB stars may be ubiquitous, and a connection
  between projected stellar rotation velocity and wind activity is well
  established. However, the origin of this connection is unknown. To
  probe the nature of the rotation connection, several of the attendees
  at the workshop on Instability and Variability of Hot-Star Winds
  drafted an IUE observing proposal. The goal of this program was to
  follow three stars for several rotations to determine whether the
  rotation connection is correlative or causal. The stars selected for
  monitoring all have rotation periods &lt;=5 days. They were HD 50896
  (WN5), HD 64760 (B0.5 Ib), and HD 66811 [ zeta Pup; O4 If(n)]. During
  16 days of nearly continuous observations in 1995 January (dubbed the
  "MEGA" campaign), 444 high-dispersion IUE spectra of these stars were
  obtained. This Letter presents an overview of the results of the MEGA
  campaign and provides an introduction to the three following Letters,
  which discuss the results for each star.

Title: HST/GHRS Observations of the beta Pictoris System: Basic
    Parameters of the Age of the System
Authors: Lanz, Thierry; Heap, Sara R.; Hubeny, Ivan
Bibcode: 1995ApJ...447L..41L
Altcode:
  We have reevaluated the basic parameters and age of the A5 IV--V star,
  beta Pictoris, making use of new observations obtained by the Goddard
  High-Resolution Spectrograph aboard the Hubble Space Telescope and
  using modern methods of atmospheric modeling and spectral synthesis. We
  derive stellar parameters appropriate to its spectral type (Teff =
  8200 +/- 150 K, log g = 4.25 +/- 0.1) including a normal (solar)
  metallicity. When dated by comparison with current evolutionary tracks,
  we find that (1) the star is apparently "underluminous"---a situation we
  attribute to (gray) extinction by the disk---and (2) the star is either
  a pre--main-sequence (PMS) star nearing the zero-age main sequence
  (ZAMS), or it is a main-sequence star older than 0.3 Gyr. Given the
  apparent youth of the disk as inferred from its high density, we judge
  the PMS interpretation as most likely.

Title: A Quantitative Study of Limb Darkening in Accretion Disks
Authors: Diaz, M. P.; Wade, R. A.; Hubeny, I.
Bibcode: 1995AAS...186.0911D
Altcode: 1995BAAS...27..825D
  The effect of limb darkening in the UV spectra of accretion disks
  is evaluated using disk models. Limb darkening correction factors
  are derived for a grid of binary system parameters and orbital
  inclinations. Continuum radial emissivity distributions and a
  description of the local limb darkening effect are presented for a
  wide range of physical conditions. The behavior of the synthetic line
  profiles and their disk diagnostic capabilities are also discussed.

Title: Non-LTE Line-blanketed Model Atmospheres of Hot Stars. II. Hot,
    Metal-rich White Dwarfs
Authors: Lanz, T.; Hubeny, I.
Bibcode: 1995ApJ...439..905L
Altcode:
  We present several model atmospheres for a typical hot metal-rich DA
  white dwarf, T<SUB>eff</SUB> = 60,000 K, log g = 7.5. We consider
  pure hydrogen models, as well as models with various abundances
  of two typical 'trace' elements-carbon and iron. We calculte a
  number of Local Thermodynamic Equilibrium (LTE) and non-LTE models,
  taking into account the effect of numerous lines of these elements
  on the atmospheric structure. We demostrate that while the non-LTE
  effects are not very significant for pure hydrogen models, except for
  describing correctly the central emission in H-alpha they are essential
  for predicting correctly the ionization balance of metals, such as
  carbon and iron. Previously reported discrepancies in LTE abundances
  determinations using C III and C IV lines are easily explained by
  non-LTE effects. We show that if the iron abundance is larger than
  10<SUP>-5</SUP>, the iron line opacity has to be considered not only for
  the spectrum synthesis, but also in the model construction itself. For
  such metal abundances, non-LTE metal line-blanketed models are needed
  for detailed abundance studies of hot, metal-rich white dwarfs. We also
  discuss the predicted Extreme Ultraviolet (EUV) spectrum and show that
  it is very sensitive to metal abundances, as well as to non-LTE effects.

Title: Hubble Space Telescope FOS Spectroscopy of the
Ultrashort-Period Dwarf Nova WZ Sagittae: The Underlying Degenerate
Authors: Sion, Edward M.; Cheng, F. H.; Long, Knox S.; Szkody, Paula;
   Gilliland, Ron L.; Huang, Min; Hubeny, Ivan
Bibcode: 1995ApJ...439..957S
Altcode:
  Two consecutive Hubble Space Telescope (HST) Faint Object Spectrograph
  (FOS) spectra of the exposed white dwarf in the ultrashort-period,
  high-amplitude, dwarf nova WZ Sge, reveal a rich absorption line
  spectrum of neutron carbon and ionized metals, the Stark-broadened
  Lyman-alpha absorption wing, the H2 quasi-molecular Lyman-alpha
  'satellite' absorption line, and a double-peaked C IV emission line
  which is variable with orbital phase. A synthetic spectral analysis of
  the white dwarf yields T<SUB>eff</SUB> = 14,900 K +/- 250 K, log g =
  8.0. In order to fit the strongest C I absorption lines and account for
  the weakness of the silicon absorption lines, the abundance of carbon
  in the photosphere must be approximately 0.5 solar, silicon abundance
  is 5 x 10<SUP>-3</SUP> solar, with all other metal species appearing to
  be 0.1-0.001 times solar. The H2 quasi-molecular absorption is fitted
  very successfully. The photospheric metals have diffusion timescales of
  fractions of a year, and thus they must have been accreted long after
  the 1978 December outburst. The source of the most abundance metal,
  carbon, is considered. If the time-averaged accretion rate during
  quiescence is low enough for diffusive equilibrium to prevail, then the
  equilibrium accretion rate pf neutron carbon is 7 x 10<SUP>-16</SUP>
  solar mass/yr. A convective dredge-up origin for the concentration of
  carbon is extremely unlikely, given that the white dwarf atmosphere
  is H-rich while in single degenerates showing carbon and hydrogen,
  the C and H are trace elements in a helium background. Additional
  implications are explored.

Title: Non-LTE Line-blanketed Model Atmospheres of Hot
    Stars. I. Hybrid Complete Linearization/Accelerated Lambda Iteration
    Method
Authors: Hubeny, I.; Lanz, T.
Bibcode: 1995ApJ...439..875H
Altcode:
  A new munerical method for computing non-Local Thermodynamic Equilibrium
  (non-LTE) model stellar atmospheres is presented. The method, called the
  hybird complete linearization/accelerated lambda iretation (CL/ALI)
  method, combines advantages of both its constituents. Its rate of
  convergence is virtually as high as for the standard CL method,
  while the computer time per iteration is almost as low as for the
  standard ALI method. The method is formulated as the standard complete
  lineariation, the only difference being that the radiation intensity
  at selected frequency points is not explicity linearized; instead,
  it is treated by means of the ALI approach. The scheme offers a wide
  spectrum of options, ranging from the full CL to the full ALI method. We
  demonstrate that the method works optimally if the majority of frequency
  points are treated in the ALI mode, while the radiation intensity at a
  few (typically two to 30) frequency points is explicity linearized. We
  show how this method can be applied to calculate metal line-blanketed
  non-LTE model atmospheres, by using the idea of 'superlevels' and
  'superlines' introduced originally by Anderson (1989). We calculate
  several illustrative models taking into accont several tens of thosands
  of lines of Fe III to Fe IV and show that the hybrid CL/ALI method
  provides a robust method for calculating non-LTE line-blanketed model
  atmospheres for a wide range of stellar parameters. The results for
  individual stellar types will be presented in subsequent papers in
  this series.

Title: Non-LTE Line Blanketed Model Atmospheres of Hot, Metal-Rich
    White Dwarfs
Authors: Hubeny, I.; Lanz, T.
Bibcode: 1995LNP...443...98H
Altcode: 1995whdw.conf...98H
  No abstract at ADS

Title: Hydrogene line profiles
Authors: Hubeny, I.
Bibcode: 1995HiA....10..411H
Altcode:
  No abstract at ADS

Title: EUVE Spectroscopy of epsilon Canis Majoris (B2 II) from 70
    to 730 Angstrom
Authors: Cassinelli, J. P.; Cohen, D. H.; Macfarlane, J. J.; Drew,
   J. E.; Lynas-Gray, A. E.; Hoare, M. G.; Vallerga, J. V.; Welsh, B. Y.;
   Vedder, P. W.; Hubeny, I.; Lanz, T.
Bibcode: 1995ApJ...438..932C
Altcode:
  We present spectra of the brightest stellar source of extreme
  ultraviolet (EUV) radiation longward of 400 A, the B2 II star, epsilon
  CMa. These data were taken with the three spectrometers aboard the
  NASA Extreme Ultraviolet Explorer satellite (EUVE) during the first
  cycle of pointed observations. We report on our initial studies of
  the continuum and line spectrum of the stellar photosphere in the
  320 to 730 A region, and on the wind emission lines observed in the
  170-375 A region. This is the first EUV spectrum of an early-type
  star, and thus makes epsilon CMa the most comprehensively observed B
  star from the X-ray to infrared regimes. The radiation in both the H
  Lyman continuum and He I continuum (shortward of 504 A) are found to
  be significantly greater than predicted by both Local Thermodynamic
  Equilibrium (LTE) and non-LTE model atmospheres. Since epsilon CMa
  also exhibits a mid-infrared excess, this points to the outer layers
  being warmer than the models indicate. The anomalously large Lyman
  continuum flux, combined with the very low column density measured in
  the direction toward this star implies that it is the dominant source
  of hydrogen ionization of the local interstellar medium in the immediate
  vicinity of the sun. All of the lines predicted to be strong from model
  atmospheres are present and several wind absorption features are also
  identified. We have detected emission lines from highly ionized iron
  that are consistent with the ROSAT Position Sensitive Proportional
  Counter (PSPC) observations if a multi-temperature emission model is
  used, and the assumption is made that there is significant absorption
  beyond that of the neutral phase of the ISM. The spectrum shows strong
  O III 374 A line emission produced by the Bowen flourescence mechanism,
  which has not previously been observed in the spectra of hot stars.

Title: A Spectrum Synthesis Program for Binary Stars with Optically
    Thick Accretion Disks
Authors: Linnell, A. P.; Hubeny, I.
Bibcode: 1994AAS...185.8505L
Altcode: 1994BAAS...26.1460L
  We recently reported a spectrum synthesis program for binary stars
  (Linnell &amp; Hubeny, 1994, ApJ, 434, Oct.20). That program now has
  been extended to include the case of an optically thick accretion
  disk associated with either of the two stellar components. Our model
  of the accretion disk uses the Pringle expression (Pringle, 1981,
  ARA&amp;A, 19, 137) for T_eff values on the accretion disk face,
  and the results of Hubeny and Plavec (1981, ApJ, 102, 1156) for rim
  T_eff values. The treatment of the stellar components is the same
  as in our 1994 paper. The program divides the rim into NRIM latitude
  values, typically 9, and divides the visible accretion disk face into
  NRING concentric ring boundaries, typically 31. The individual rings
  (for both the rim and the face) subdivide into NSEG pixels, typically
  101. An individual synthetic spectrum, appropriate to the local T_eff
  value, is attached to each pixel. For illustration purposes we have used
  synthetic spectra prepared from Kurucz atmospheres. The extended program
  constructs a synthetic spectrum for the accretion disk face, rim, the
  separate stellar components, and the entire system by producing a sum
  of contributions, at each wavelength (with due allowance for Doppler
  shift), from each visible pixel on the accretion disk or the separate
  stellar components, weighted by the projected area of the pixel. A
  separate program establishes a visibility key for each pixel and cosine
  of the zenith angle of the observer as seen from each pixel, for the
  current value of orbital inclination and orbital longitude. These data
  combine with synthetic spectra in the spectrum synthesis program to
  determine line of sight light intensities at each wavelength, i.e.,
  the contributions needed for the sum. Separate data from related
  programs permit a plot of the system projected on the plane of the
  sky. This project received partial support from NSF grant AST9020459.

Title: HST spectrally-resolved accretion disk maps of UX UMa in
    the ultraviolet
Authors: Baptista, R.; Long, K.; Horne, K.; Hubeny, I.; Mauche, C. W.;
   Rutten, R. G. M.; Wade, R. A.
Bibcode: 1994AAS...18511605B
Altcode: 1994BAAS...26.1514B
  We present spectrally-resolved eclipse maps of the UX UMa accretion
  disk in the spectral region 1170--2400 Angstroms. The analysis is
  based on low-dispersion time-resolved spectroscopy during eclipse,
  obtained with the HST Faint Object Spectrograph. The out-of-eclipse
  spectra show prominent emission lines (CIII lambda 1176, Lyalpha ,
  NV lambda 1240, SiIV lambda 1400, CIV lambda 1550) as well as many
  absorption features and possibly a broad absorption band centered
  at about 1900 Angstroms. HeII lambda 1640 appears as a weak emission
  line. At mid-eclipse the continuum flux is reduced by a factor ~ 3,
  while the emission lines are much less affected by the eclipse and
  some of the lines that are seen in absorption in the out-of-eclipse
  spectra appear in emission. UV continuum light curves show significant
  flickering activity outside of eclipse, relatively much stronger
  than observed in the optical range. The eclipses are deep and steep
  in the continuum with an asymmetry in their egress portion, however
  no clear evidence of a compact bright spot is seen. The spectra were
  divided into passbands ( ~ 40 Angstroms in the continuum and ~ 3000
  Km/s in the emission lines) and light curves were extracted for each
  one. Maximum-entropy eclipse mapping techniques were used to solve
  for a map of the disk brightness distribution and for the flux of
  an additional uneclipsed component in each band. Radial brightness
  temperature profiles and spatially-resolved disk spectra derived from
  these maps are presented and discussed.

Title: HST/GHRS Observations of beta Pictoris
Authors: Heap, S. R.; Lanz, T.; Hubeny, I.; Lindler, D.
Bibcode: 1994AAS...185.4812H
Altcode: 1994BAAS...26.1389H
  In September 1994, we obtained HST/GHRS spectra and maps of beta
  Pic (HD 39060) and its surrounding disk. In this paper, we report
  our preliminary findings concerning the star and circumstellar gas
  disk. Both Stromgren photometry and Geneva photometry (as listed
  by SIMBAD) yield the following parameters for the star: T_eff=8200
  +/- 50 K log g = 4.25 +/- 0.05 [Fe/H] = -0.1 +/- 0.2 To refine the
  estimated metallicity, we have compared the GHRS ultraviolet spectra
  with model spectra. Our model of beta Pic incorporates both a LTE
  stellar atmosphere plus a circumstellar gas disk, treated in a first
  approximation as a homogeneous, absorbing slab at T=5,000 K with
  a column density, N_H=2x10(19) cm(-2) . We confirm that the star
  has a near-solar metallicity. We have compared the derived stellar
  parameters with evolutionary models for Z=0.017. For reference, a ZAMS
  star having a T_eff=8,200 K has a mass, M ~1.72 M_sun, and a gravity,
  log g= 4.37. The somewhat low surface gravity of beta Pic suggests that
  the star has evolved slightly off the ZAMS or is still in the pre-main
  sequence phase. In either case, it should be somewhat more luminous
  than a 1.72M_sun ZAMS star. However, its absolute magnitude, M_V= 2.70
  (for a distance of 17 pc) is 0.21 mag fainter than a M=1.72 M_sun star
  on the ZAMS. We therefore conclude that (1) the dust disk must diminish
  light from the star, and (2) it is entirely possible that beta Pic is
  a very young star. Both conclusions raise problems for interpreting
  observations of the dust disk (c.f. Paresce, 1991, A&amp;A, 247, L25).

Title: HST/FOS Spectroscopy of the Central Star of NGC 7027
Authors: Hubeny, I.; Heap, S. R.; Lanz, T.
Bibcode: 1994AAS...185.4710H
Altcode: 1994BAAS...26.1385H
  With its rich UV-optical-IR spectrum, NGC 7027 has been the target
  of choice for study of important physical processes including
  charge-exchange, dust-quenching of nebular lines, PDR's, extended-red
  emission, etc. Surprisingly little, though, is known about the central
  star, because the star is embedded in such a bright nebula. With
  the success of the HST servicing mission, it is now possible to
  carry out direct studies of the central star. Here, we report on
  HST/FOS spectroscopy of the central star. In August 1994, we obtained
  FOS/G400H, G570H spectra of NGC 7027 with the central star centered
  in the 1farcs 0 aperture. The spectra cover the wavelength range,
  3250-6750 Angstroms. The spectra are of excellent quality. For example,
  at lambda 4800 Angstroms, the S/N=76 per resolution element, and the
  star contributes 94% of the observed continuum flux. Other very hot
  stars, i.e. PG 1159 stars, are known to show high-ionization lines,
  such as O VI lambda lambda 3811,3834, C IV lambda 4441, or C V lambda
  4945, etc. To our surprise, these lines are absent in the spectrum
  of the central star. In fact, the stellar spectrum is apparently
  featureless. We have therefore used the absence of spectral features
  to put limits on effective temperature and chemical composition of the
  central star. We are constructing a small grid of line-blanketed NLTE
  model atmospheres for the effective temperatures range 100,000 K &lt;
  T_eff &lt; 250,000 K, 5.8 &lt; log g &lt; 7.5, and for two compositions:
  (i) a H-rich (solar) composition, and (ii) a C-O enriched atmosphere,
  typical of PG 1159 stars. We will report on the results of this
  analysis.

Title: NLTE Line-blanketed Model Atmosphere Analysis of the hot
    Subdwarf BD +75° 325
Authors: Lanz, T.; Hubeny, I.; Heap, S. R.
Bibcode: 1994AAS...185.8005L
Altcode: 1994BAAS...26.1447L
  With the Goddard High Resolution Spectrograph aboard HST, we have
  recorded a high-resolution, high signal-to-noise ratio, far ultraviolet
  spectra of the hot subdwarf, BD +75° 325. Because of the low apparent
  rotational velocity (V sin i &lt; 20 km/s) of the star, the high
  quality of the spectra and our newly developed NLTE line-blanketed
  model atmospheres, we have an unprecedented opportunity to derive
  accurate stellar parameters. With our hybrid CL/ALI method, we have
  constructed a small grid of NLTE line-blanketed model atmospheres for
  hot subdwarfs. These model atmospheres include consistently about
  200 NLTE levels (or superlevels) of H, He, C, N, O, Si, Fe and Ni,
  and all transitions between them. Individual atomic levels of iron and
  nickel are merged into a relatively small number of superlevels. The
  cross-sections of the transitions between superlevels are represented by
  NLTE Opacity Distribution Functions. This grid of NLTE model atmospheres
  is used for a thorough analysis of BD +75° 325, which then provides
  in addition a ``real'' check of our methodology. Our results show that
  BD +75° 325 is a He enriched star, whose surface exhibit CNO-cycle
  products (N-rich and C-deficient). The very rich Fe v and Fe vi line
  spectra can only be reproduced by a significant overabundance of iron
  (about 5 to 10 times solar). With our metal line blanketed NLTE model
  atmospheres, we are now able to reproduce the deep line cores in the
  ultraviolet spectrum assuming a microturbulence of 5-10 km/s. Moreover,
  the line blanketed models are necessary to match the H i/He ii line
  cores in the visual spectrum (models including only H and He produce
  too shallow lines). Finally, we have found a weak asymmetry of the
  N v resonance line profiles, which can be attributed to a weak wind
  with M = 9+/- 2times 10(-11) M_sun /yr.

Title: Analysis of the VW Hyi's Superoutburst FOS/HST Spectrum:
    a Heated White Dwarf and a Disrupted Disk
Authors: Huang, M.; Sion, E. M.; Hubeny, I.; Cheng, F. H.; Szkody, P.
Bibcode: 1994AAS...18513104H
Altcode: 1995BAAS...27..770H
  No abstract at ADS

Title: GHRS Spectroscopy of Individual Stars in R136a
Authors: Heap, Sara R.; Ebbets, Dennis; Malumuth, Eliot M.; Maran,
   Stephen P.; de Koter, Alex; Hubeny, Ivan
Bibcode: 1994ApJ...435L..39H
Altcode:
  The installation of the Corrective Optics Space Telescope Axial
  Replacement (COSTAR) Instrument on the Hubble Space Telescope (HST)
  makes it possible to observe stars in very crowded regions with high
  spatial and spectral purity. To demonstrate this capability, we have
  used the Goddard High Resolution Spectrograph (GHRS) to obtain spectra
  of two stars in the dense center of the 30 Doradus ionizing cluster:
  R136a5, and its nearest neighbor, R136a2, only 0.17 sec away. R136a5 is
  shown to ben an O3f/WN star, while R136a2 is a WN4-w star. From both
  Wide Field/Planetary Camera (WFPC) photometry and GHRS, spectroscopy
  we estimate the following properties of R136a5: T<SUB>eff</SUB> =
  42,500 K, R = 16.4 solar radius, L<SUB>bol</SUB> = 8 x 10<SUP>5</SUP>
  solar luminosity, and M approx. equals 50 solar mass -- all indicating
  that, despite its spectral type, R136a5, as indicated by the strength
  of He II lambda 1640 emission. The observed mass-loss rate, dot-M =
  1.8 x 10<SUP>-5</SUP> solar mass/yr, is an order of magnitude higher
  than is assumed by current stellar evolutionary models. We argue that
  this high rate of mass loss will alter drastically the evolutionary
  path of R136a5. If so, evolutionary models for massive stars require
  substantial revision.

Title: Theoretical Modeling of GHRS Observations of the Of/WN-Type
    Star R136a5
Authors: de Koter, Alex; Hubeny, Ivan; Heap, Sara R.; Lanz, Thierry
Bibcode: 1994ApJ...435L..71D
Altcode:
  We present a theoretical analysis of the Hubble Space Telescope (HST)
  Goddard High Resolution Spectrograph (GHRS) spectrum of R136a5,
  an O3fWN star in the R136a cluster in 30 Doradus. Using non-LTE
  extended and expanding model atmospheres, we find a surprisingly high
  mass-loss rate dot-M = 1.8 +/- 0.5 x 10<SUP>-5</SUP> solar mass/yr and
  an effective temperature T<SUB>eff</SUB> = 42.5 +/- 2.5 kK. With the
  observed visual magnitude, this implies a radius R<SUB>*</SUB> = 17 +/-
  2 solar radius and a solar luminosity L = 8.5 +/- 1 x 10<SUP>5</SUP>
  solar luminosity. We discuss possible sources of the uncertainties
  in the derived stellar parameters and conclude that the effective
  temperature may be underestimated; however, if so, the value of the
  mass-loss rate would not be affected.

Title: A Spectrum Synthesis Program for Binary Stars
Authors: Linnell, Albert P.; Hubeny, Ivan
Bibcode: 1994ApJ...434..738L
Altcode:
  A new program produces synthetic spectra of binary stars at arbitrary
  values of orbital longitude, including longitudes of partial or
  complete eclipse. The stellar components may be distorted, either
  tidally or rotationally, or both. Either or both components may be
  rotating nonsynchronously. We illustrate the program performance with
  two cases: EE Peg, an eclipsing binary with small distortion, and SX
  Aur, an eclipsing binary that is close to contact.

Title: On the strategy of future observations and modeling of the
    β Lyrae system.
Authors: Hubeny, I.; Harmanec, P.; Shore, S. N.
Bibcode: 1994A&A...289..411H
Altcode:
  β Lyr is an enigmatic object. Despite several decades of concentrated
  observational and theoretical effort, our understanding of the system
  is still rather poor. We discuss two existing structural models of the
  system, the massive torus model of Wilson (1981), and the low mass
  accretion disk model of Hubeny &amp; Plavec (1991). In particular,
  we answer recent criticism of the low mass disk model expressed by
  the proponents of the massive disk hypothesis. We show that although
  both theories have a large degree of internal consistency, there are
  several serious physical objections against the massive disk model. In
  particular, such a model requires unrealistically low viscosity
  (large Reynolds number). Moreover, such massive disk is likely to
  be dynamically unstable. Finally, we propose several observational
  and theoretical approaches that could lead to construction of a more
  physically realistic model of the β Lyr system.

Title: Dynamic Processes in Be Star Atmospheres. II. He i 2P--nD
    Line Formation in lambda Eridani (Outburst)
Authors: Smith, Myron A.; Hubeny, Ivan; Lanz, Thierry; Meylan, Thomas
Bibcode: 1994ApJ...432..392S
Altcode:
  The He I lambda 6678 line of early Be stars generally shows violet (V)
  and red (R) emission whenever hydrogen alpha emission is present, but
  its use as a diagnostic has been handicapped by a poor understanding of
  the processes that drive it into emission. In an attempt to address this
  problem we obtained three series of eschelle spectra of the first two
  members of the singlet and triplet 2P-nD series of lambda Eri (B2e)
  during 1992 November 3-5 at Kitt Peak. During these observations
  lambda 6678 showed substantial emission variability in both the
  wings and central profile, providing an opportunity to compare its
  behavior with that of the lambda 4922, lambda 5876, and lambda 4471
  lines. We found that the responses of the lines were different in
  several respects. Whereas the emissions in the V wings of all four
  lines scaled together, the R wing of the lambda 4922 line invariably
  responded with increased absorption whenever the R wing of lambda 6678
  line showed increased emission. These same trends occurred within
  the central photospheric profiles. The R-wing behavior shows that
  much, but not all of the emission in lambda 6678 is caused by matter
  projected against the stellar disk. The excitation temperatures of
  the neighboring 2<SUP>1</SUP> P transitions, lambda 6678 and lambda
  4922 must be greater than and less than the photospheric continuum
  temperature, respectively. We have investigated departures from local
  thermodynamic equilibrium (LTE) for the He I spectrum in a variety of ad
  hoc, perturbed model atmospheres. We have found only one way to cause
  the source function of lambda 6678 to increase so strongly, namely,
  by increasing the atmospheric temperature in the line formation region
  to 30,000 - 40,000 K. This effect was discovered by Auer and Mihalas
  for O3-O4 atmospheric models, but it has not been applied to active
  B stars. Our models suggest that lambda 6678 emission in Be stars can
  be used as a sensitive monitor of localized hot spots on these stars'
  surfaces. The energies involved in heating the active portions of the
  atmosphere are too high to be produced by gravitational infall. This
  leaves magnetically induced flares among the few known processes on
  the surfaces of stars capable of sustaining this energy level.

Title: A Spectrum Synthesis Program for Binary Stars
Authors: Linnell, A. P.; Hubeny, I.
Bibcode: 1994AAS...184.0606L
Altcode: 1994BAAS...26..868L
  A new computer program produces synthetic spectra of binary stars
  at arbitrary values of orbital longitude, including longitudes of
  partial or complete eclipse. The stellar components may be distorted,
  either tidally or rotationally, or both. Either or both components may
  be rotating non-synchronously. We illustrate the program performance
  with two cases: EE Peg, an eclipsing binary with small distortion and
  SX Aur, an eclipsing binary that is close to contact.

Title: HST Eclipse Mapping of Dwarf Nova OY Carinae in Quiescence:
    an ``Fe II Curtain'' with Mach 6 Velocity Dispersion Veils the
    White Dwarf
Authors: Horne, Keith; Marsh, T. R.; Cheng, F. H.; Hubeny, Ivan;
   Lanz, Theirry
Bibcode: 1994ApJ...426..294H
Altcode:
  Hubble Space Telescope (HST) observations of the eclipsing dwarf nova OY
  Car in its quiescent state are used to isolate the ultraviolet spectrum
  (1150-2500 A at 9.2 A Full Width at Half Maximum (FWHM) resolution)
  of the white dwarf, the accretion disk, and the bright spot. The
  white dwarf spectrum has a Stark-broadened photospheric L(alpha)
  absorption, but is veiled by a forest of blended Fe II features that
  we attribute to absorption by intervening disk material. A fit gives
  T<SUB>w</SUB> approx. = 16.5 x 10<SUP>3</SUP> K for the white dwarf
  with a solar-abundance, log g = 8 model atmosphere, and T approx. =
  10<SUP>4</SUP> K, n<SUB>e</SUB> approx. = 10<SUP>13</SUP>/cu cm,
  N<SUB>H</SUB> approx. = 10<SUP>22</SUP> sq cm, and velocity dispersion
  delta V approx. = 60 km/s for the veil of homogeneous solar-abundance
  local thermodynamic equilibrium (LTE) gas. The veil parameters probably
  measure characteristic physical conditions in the quiescent accretion
  disk or its chromosphere. The large velocity dispersion is essential
  for a good fit; it lowers (chi square)/778 from 22 to 4. Keplerian shear
  can produce the velocity dispersion if the veiling gas is located at R
  approx. = 5 R<SUB>W</SUB> with (delta R)/R approx. = 0.3, but this model
  leaves an unobscured view to the upper hemisphere of the white dwarf,
  incompatible with absorptions that are up to 80% deep. The veiling
  gas may be in the upper atmosphere of the disk near its outer rim,
  but we then require supersonic (Mach approx. = 6) but sub-Keplerian
  (delta V/V<SUB>Kep</SUB> approx. = 0.07) velocity disturbances in
  this region to produce both the observed radial velocity dispersion
  and vertical motions sufficient to elevate the gas to z/R = cos i
  = 0.12. Such motions might be driven by the gas stream, since it
  may take several Kepler periods to reestablish the disk's vertical
  hydrostatic equilibrium. The temperature and column density of the
  gas we see as Fe II absorption in the ultraviolet are similar to what
  is required to produce the strong Balmer jump and line emissions seen
  in optical spectra of OY Car and similar quiescent dwarf novae. The
  outer accretion disk is detected at mid-eclipse with a spectrum that
  rises from 0.05 to 0.3 mJy between 2000 and 2500 A, consistent with
  combinations of cool blackbodies, blended Fe II emission lines,
  and Balmer continuum emission. The total disk flux density is 0.5
  mJy at 2500 A, and this shallow disk eclipse implies a roughly flat
  surface brightness distribution. The bright spot, somewhat bluer than
  the disk, has a flux density rising from 0.05 to 0.15 mJy between
  1600 and 2500 A. The C IV emission line has a broad shallow eclipse,
  but the radial velocity variations observed during the eclipse do not
  clearly distinguish between a disk or wind origin. The only possible
  indications of boundary layer emission are fast UV flares that appear
  to arise from near the central object -- not from the bright spot.

Title: Observations of the Bright Novalike Variable IX Velorum with
    the Hopkins Ultraviolet Telescope
Authors: Long, Knox S.; Wade, Richard A.; Blair, William P.; Davidsen,
   Arthur F.; Hubeny, Ivan
Bibcode: 1994ApJ...426..704L
Altcode:
  The Hopkins Ultraviolet Telescope, an experiment flown on the Space
  Shuttle as part of the Astro-1 mission, was used to obtain a spectrum
  of the novalike variable IX Vel (= CPD -48 deg 1577) in the wavelength
  range 830-1860 A. The observation revealed a rich absorption-line
  and continuum spectrum that peaks near 1050 A at a flux of 1.6 x
  10<SUP>-11</SUP> ergs/sq cm/s/A. In the sub-Lyman-alpha region, some
  of the more prominent absorption lines are S VI lambda lambda-933, 945,
  C III lambda-977, Lyman-beta, O VI lambda lambda-1032, 1038, P V lambda
  lambda-1118, 1128, and C III lambda-1176. No emission was detected below
  the Lyman limit. The overall continuum shape of IX Vel in the FUV can be
  approximated using models of an optically thick accretion disk in which
  the integrated spectrum has been constructed by summing model stellar
  atmospheres or proper disk model spectra. However, if the distance to
  IX Vel is approximately 95 pc, standard disk models without reddening
  cannot simultaneously reproduce the color and flux in the UV. While
  interstellar reddening can reconcile this difference, the amount of
  reddening appears inconsistent with the absence of a 2200 A bump in
  the spectrum and the very low H I column density measured along the
  line of sight. Improved fits to the data can be obtained by modifying
  the accretion disk stucture within three white dwarf radii. None
  of the models reproduces the profiles of the Li- and Na-like ions,
  which are observed as strong but relatively narrow absorption lines,
  and which are almost surely due to a wind above the disk.

Title: The Iron Curtain Effect in the Ultraviolet Spectra of Dwarf
    Novae Z Cha and OY CAR
Authors: Wade, R. A.; Cheng, F. H.; Hubeny, I.
Bibcode: 1994AAS...184.4605W
Altcode: 1994BAAS...26Q.936W
  We model the ultraviolet spectra of the quiescent dwarf novae Z Cha
  and OY Car, obtained in 1986 with the SWP camera of the International
  Ultraviolet Explorer, on the assumption that the flux is due to the
  central white dwarf seen through a haze of absorbing material. This
  material is optically thin in the continuum but thick in the lines
  of many atomic species, chiefly of iron-peak elements. These IUE
  observations are long exposures covering several orbits, and so they
  do not unambiguously refer to the white dwarf alone. This differs
  from the 1991 observation of OY Car's white dwarf by the Faint
  Object Spectrograph on HST, which was made using time-tagged eclipse
  spectrophotometry as discussed in Horne et al. (1994). The HST data
  also have the advantage of a photon counting detector. Nevertheless,
  there is interest in using the IUE data to observe the so-called
  ``Iron Curtain'' of OY Car at a different epoch, and to extend the
  study of the Iron Curtain to another dwarf nova in quiescence, Z
  Cha. Results in terms of multiple-parameter fits for the white dwarf
  temperature and solid angle, and the column density, temperature, number
  density, and turbulent broadening of the Iron Curtain of each star,
  are discussed. An attempt is made to be consistent with the optical
  photometry of the white dwarfs, as determined by Wood et al. (1986,
  1989). Supported by NASA grant NAG 5-703 and NASA/STScI grant GO-2380.

Title: NLTE Model Stellar Atmospheres: The Hybrid CL/ALI Method
Authors: Lanz, T.; Hubeny, I.
Bibcode: 1994AAS...184.4011L
Altcode: 1994BAAS...26..924L
  A new numerical method for computing sophisticated NLTE model
  stellar atmospheres is presented. The method, called the hybrid
  Complete Linearization/Accelerated Lambda Iteration (CL/ALI) method,
  combines advantages of both its constituents. Its rate of convergence
  is virtually as high as for the standard CL method, while the computer
  time per iteration is almost as low as for the standard ALI method. The
  method is formulated as the standard complete linearization; the only
  difference being that the radiation intensity at selected frequency
  points is not explicitly linearized; instead, it is treated by means
  of the ALI approach. The scheme offers a wide spectrum of options,
  ranging from the full CL to the full ALI method. We demonstrate
  that the method works optimally if the majority of frequency points
  are treated in the ALI mode, while the radiation intensity at a few
  (typically 2 - 30) frequency points is explicitly linearized. We show
  how this method can be applied to calculate metal line blanketed NLTE
  model atmospheres of hot stars. We use the idea of ``superlevels'' and
  ``superlines'' introduced originally by Anderson (1989). We calculate
  several illustrative models taking into account several tens of thousand
  of lines of Fe iii to Fe vi, and show that the hybrid CL/ALI method
  provides a robust method for calculating NLTE line blanketed model
  atmospheres for a wide range of stellar parameters. This work was
  supported in part by NASA grants NAGW-3025 and NAGW-3834.

Title: GHRS observations and theoretical modeling of early type
    stars in R136a
Authors: de Koter, A.; Heap, S.; Hubeny, I.; Lanz, T.; Hutchings,
   J.; Lamers, H. J. G. L. M.; Maran, S.; Schmutz, W.
Bibcode: 1994AAS...184.3106D
Altcode: 1994BAAS...26..909D
  We present the first spectroscopic observations of individual stars in
  R136a, the most dense part of the starburst cluster 30 Doradus in the
  LMC. Spectra of two stars are scheduled to be obtained with the GHRS
  on board the HST: R136a5, the brightest of the complex and R136a2,
  a Wolf-Rayet star of type WN. The 30 Doradus cluster is the only
  starburst region in which individual stars can be studied. Therefore,
  quantitative knowledge of the basic stellar parameters will yield
  valuable insight into the formation of massive stars in starbursts and
  into their subsequent evolution. Detailed modeling of the structure
  of the atmosphere and wind of these stars will also lead to a better
  understanding of the mechanism(s) that govern their dynamics. We
  present the first results of our detailed quantitative spectral
  analysis using state-of-the-art non-LTE model atmospheres for stars
  with extended and expanding atmospheres. The models are computed using
  the Improved-Sobolev Approximation wind code (ISA-WIND) of de Koter,
  Schmutz &amp; Lamers (1993, A&amp;A 277, 561), which has been extended
  to include C, N and Si. Our model computations are not based on the
  core-halo approximation, but use a unified treatment of the photosphere
  and wind. This approach is essential for Wolf-Rayet stars. Our synthetic
  spectra, dominated by the P Cygni profiles of the UV resonance lines,
  also account for the numerous weak metal lines of photospheric origin.

Title: Physics of Massive Hot Stars
Authors: Hubeny, I.
Bibcode: 1994AAS...184.3401H
Altcode: 1994BAAS...26..913H
  We discuss the impact of HST on our understanding of physics of hot
  massive stars. Since these stars are very luminous, they can be studied
  as individual stars in several parent galaxies. In order to take full
  advantage of the high spectral resolution and high signal-to-noise
  ratio offered by the HST spectra, new highly accurate and reliable
  methods of spectroscopic analysis have to be developed. We show that
  thanks to the recent dramatic advances in fast numerical methods it
  is now possible to construct model atmospheres of an unprecedented
  degree or realism and accuracy. We concentrate on two basic issues
  of the modern stellar atmospheres models of hot stars. First, we
  discuss the effects of departures from local thermodynamic equilibrium
  (referred to as non-LTE or NLTE). We show that model atmospheres are
  now becoming avaliable that include the opacity of tens to hundred
  thousand metal lines in full NLTE (the so-called NLTE line-blanketed
  model atmospheres). It is now possible to derive the basic stellar
  parameters (effective temperature, luminosity, chemical composition)
  to a high degree of accuracy. Second, we discuss models which do not
  employ the traditional core-halo approximation, i.e. an arbitrary
  separation of the static photosphere and the dynamic stellar wind --
  the so-called unified model atmospheres. We review the recent research
  effort in this direction, and show several interpretational consequences
  of this methodological improvement.

Title: The Discovery of NI V in the Photospheres of the Hot DA White
    Dwarfs RE 2214-492 and G191-B2B
Authors: Holberg, J. B.; Hubeny, I.; Barstow, M. A.; Lanz, T.; Sion,
   E. M.; Tweedy, R. W.
Bibcode: 1994ApJ...425L.105H
Altcode:
  We have co-added six recently obtained International Ultraviolet
  Explorer (IUE) echelle spectra of the hot DA white dwarf RE 2214-492
  and 10 existing archive spectra of the well-known hot DA, G191-B2B. We
  find that both stars contain numerous weak features due to Ni V. Nickel
  is thus the second iron-group element to be found in the spectra of the
  very hottest DA white dwarfs. In addition to Ni V, we also observe Al
  III in both stars and present evidence for the possible presence of
  Ni IV and Fe IV in RE 2214-492. The presence of Ni and Al, together
  with previously reported elements, will contribute significantly to
  both the EUV opacity and to the apparent complexity of the UV spectra
  of these stars. Using Non-Local Thermodynamic Equilibrium (NLTE) model
  atmospheres we estimate the Ni abundances in RE 2214-492 the G191-B2B
  to be log(Ni/H) = -5.5 +/- 0.3 and -6.0 +/- 0.3, respectively.

Title: NLTE model stellar atmospheres with line blanketing near the
    series limits.
Authors: Hubeny, I.; Hummer, D. G.; Lanz, T.
Bibcode: 1994A&A...282..151H
Altcode:
  In this paper we study the influence of line-merging regions at the
  intermediate long-wavelength side of a continuum threshold on the
  computed model atmosphere structure and predicted spectrum. In order
  to model these regions sufficiently accurately, we have developed two
  concepts. First, we have extended the occupation probability formalism
  of Hummer and Mihalas to non-local thermodynamic equilibrium (non-LTE)
  plasmas. Second, in order to treat the very complicated opacity in
  the line merging region, we have generalized the concept of opacity
  distribution functions to treat non-LTE situations. All Rydberg states
  are consistently included within this framework, so that no arbitrary
  cutoff of high (LTE) levels is made. We have calculated several
  pure hydrogen models atmospheres for two effective temperatures,
  T<SUB>eff</SUB> = 20000 and 35000 K, and discussed the differences
  between models calculated with various treatments of the line
  merging. In particular, we have shown that the error in the predicted
  profiles of Balmer lines resulting from the neglect of line merging
  is typically of the order of 3-4%, while the errors in the far-UV
  portion of the Balmer continuum reaches 15-35%. The errors generally
  decrease with increasing effective temperature. At the same time,
  the internal accuracy of the models is shown to be about or below 0.5%
  for all predicted spectral features. We conclude that for interpreting
  current high-accuracy spectrophotometric observations models including
  the line merging are necessary, and that the formalism developed in
  this paper is capable of providing a sufficiently accurate and robust
  modeling technique.

Title: Puzzling problems of He I line formation in early B stars
Authors: Smith, M. A.; Hubeny, I.; Lanz, T.
Bibcode: 1994IAUS..162..273S
Altcode:
  No abstract at ADS

Title: The Lyman-Line Region in Models of Dwarf Nova Accretion Disks
Authors: Wade, R. A.; Hubeny, I.; Polidan, R. S.
Bibcode: 1994ASPC...56..319W
Altcode: 1994ibs..conf..319W
  No abstract at ADS

Title: HST Eclipse Mapping of the Dwarf Nova OY Carinae in
Quiescence: an "Fe II Curtain" with Mach approximately equals 6
    Velocity Dispersion Veils the White Dwarf
Authors: Horne, K.; Cheng, F. H.; Marsh, T.; Hubeny, I.; Lanz, T.
Bibcode: 1994ASPC...56..283H
Altcode: 1994ibs..conf..283H
  No abstract at ADS

Title: The Cooling of the White Dwarf in OY CAR After 1992
    Superoutburst
Authors: Cheng, F. H.; Marsh, T. R.; Horne, K.; Hubeny, I.
Bibcode: 1994AIPC..308..197C
Altcode: 1994exrb.conf..197C
  HST observations of the eclipsing dwarf nova OY Car after its 1992
  April superoutburst are used to isolate ultraviolet spectra (1150-2500
  Å at 9.2 Å FWHM resolution) of the white dwarf, the accretion disk,
  and the bright spot. The white dwarf spectra have a Stark-broadened
  photospheric Lα absorption, but are veiled by a forest of blended
  Fe II features that we attribute to absorption by intervening disk
  material. Spectral fits give white dwarf temperatures changing from
  ∼19500 K just after outburst ∼17400 K around three months after
  outburst. The temperature of intervening disk material is ∼8600
  K-9800 K; the velocity dispersion of the intervening disk material is
  ∼60-70 km/s. Fitting results also shows that the decay time of white
  dwarf temperature is ∼27 days, that is much shorter than ∼687 days
  in dwarf nova WZ Sge.

Title: Accretion in "Ordinary" Interacting Binaries
Authors: Plavec, M. J.; Hubeny, I.
Bibcode: 1994ASPC...56...87P
Altcode: 1994ibs..conf...87P
  No abstract at ADS

Title: Vertical Structure and Theoretical Spectra of Accretion Disks
Authors: Hubeny, I.
Bibcode: 1994ASPC...56....3H
Altcode: 1994ibs..conf....3H
  No abstract at ADS

Title: An Atlas of the Lyman-alpha Region for a Grid of Dwarf Nova
    Accretion Disk Models
Authors: Wade, R. A.; Hubeny, I.; Polidan, R. S.
Bibcode: 1993AAS...182.6312W
Altcode: 1993BAAS...25Q.910W
  We use the accretion disk modeling code TLUSDISK and spectrum synthesis
  tools to compute a grid of spectra between 900 and 1500 Angstroms for
  accretion disks of cataclysmic variables in quiescence. The disk models
  and spectra are calculated in LTE. A contribution from the white dwarf
  is included, for a variety of white dwarf effective temperatures. The
  occultation of part of the inner disk by the white dwarf is also
  taken into account. The contribution of a boundary layer, assumed
  to be optically thin and emitting primarily at x-ray temperatures,
  is neglected. The mass and radius of the accreting white dwarf are
  varied. The mass accretion rate, assumed to be steady, is chosen to
  reproduce the estimated luminosities of quiescent dwarf novae. The
  emergent spectra are presented for a variety of inclination angles, to
  show the effect of Doppler broadening at a resolution similar to that
  of the Hopkins Ultraviolet Telescope and somewhat better than that of
  low-dispersion IUE spectra. Comparisons of the Lyman-alpha region with
  some IUE spectra of dwarf novae in quiescence are attempted. Supported
  by NASA grant NAG 5-2125.

Title: NLTE Line Blanketed Model Atmospheres for Hot, Metal-rich
    White Dwarfs
Authors: Hubeny, I.; Lanz, T.
Bibcode: 1993AAS...182.4701H
Altcode: 1993BAAS...25..878H
  Recent observations of some hot DA white dwarfs (Feige 24, G191 B2B -
  Sion et al. 1992, Ap.J. 391, L29; Vennes et al. 1992, Ap.J. 392, L27)
  and subsequent analyses have demonstrated that their atmospheres are
  contaminated with heavy metal species with appreciable abundances. So
  far, modeling was mostly limited to calculating synthetic spectra
  (usually in LTE), based on previously calculated model atmospheres that
  were constructed assuming a simplified chemical composition. However,
  in reality the metal lines may also significantly influence the
  temperature structure, and consequently the ionization balance of some
  important species. Since the effective temperature is rather high
  (55000 to 60000 K), the NLTE effects may be important despite the
  high gravity. Therefore, in order to settle the question on metal
  abundances of hot DA white dwarfs, we need to calculate NLTE fully
  line blanketed model atmospheres. Using our previously developed
  hybrid complete linearization/accelerated lambda iteration method,
  we have calculated a set of NLTE models including H, He, C, N, O, and
  Fe, with some 13000 lines of Fe IV, Fe V and Fe VI taken into account
  explicitly in model construction. The NLTE departure coefficients
  for all levels of Fe IV, Fe V, and Fe VI are then employed in the
  spectrum synthesis program SYNSPEC. In the first part of this study,
  we present a theoretical comparison between models computed with adding
  more and more opacity sources, and show how the temperature structure
  and synthetic spectra develop. We also discuss possible errors arising
  from using an inconsistent spectrum synthesis (the metals considered
  only in the spectrum synthesis, not in the model construction). In the
  second part, we compare the computed UV spectra with with available
  observations of Feige 24 and G191 B2B, and deduce limits for the iron
  abundance of these stars.

Title: Accretion on Non-Degenerate Binary Components
Authors: Plavec, M. J.; Hubeny, I.
Bibcode: 1993AAS...182.4505P
Altcode: 1993BAAS...25Q.871P
  We are studying accretion disks in a variety of binary systems with
  non-degenerate components. Disks are modeled by program TLUSDISK, their
  detailed spectra are calculated for a range of inclination angles,
  and differential Doppler broadening due to the Keplerian rotation in
  the disk is duly included. Model spectra are compared with observed IUE
  and CCD optical spectra. We find that various combinations of the rate
  of mass transfer, mass and size of the gainer, and degree of viscosity
  in the disk can produce a wide variety of observable phenomena. Here
  we report on two cases. (1) The Algol-type eclipsing binary RY Persei
  with a relatively large gainer mass and low mass transfer rate shows
  a primary spectrum of B6 IV but with deep and strong UV circumstellar
  absorptions, corresponding to strong emissions seen during total
  eclipse. These lines are obviously formed in a layer or column
  associated with the boundary layer between the disk and the star. (2)
  The question if a symbiotic spectrum can be produced by an accretion
  disk around a small red dwarf is studied (case of CI Cygni). The
  vertical thickness of the disk strongly depends on the Reynolds number
  describing viscosity, and can be substantial for a conventional value
  of Re=5000. Since observations of this eclipsing system suggest i =
  73(deg) , Re would have to be much smaller (1000). This provides an
  interesting constraint on Re which may be exploited in future studies
  of disk viscosity. Our models predict the spectra of the various
  types of binary systems if viewed at moderate or low inclinations,
  thus offering hints for systematic searches.

Title: Observations of the White Dwarf in the U Geminorum System
    with the Hopkins Ultraviolet Telescope
Authors: Long, Knox S.; Blair, William P.; Bowers, Charles W.;
   Davidsen, Arthur F.; Kriss, Gerard A.; Sion, Edward M.; Hubeny, Ivan
Bibcode: 1993ApJ...405..327L
Altcode:
  The Hopkins Ultraviolet Telescope was used to obtain an FUV spectrum
  of U Gem about 10 d after the end of an outburst. Most of the FUV
  emission from U Gem appears to rise from the white dwarf (WD) in the
  system. Various possibilities to explain the hot component in the
  present spectrum are explored. It is most likely due to radiation
  from the boundary-layer region of the WD surface rather than from the
  accretion disk which exists in U Gem in quiescence. If the standard
  picture of boundary-layer emission is correct, then the hot component
  is not due to ongoing accretion onto the WD because the temperature
  observed is too low. Delayed emission from a viscously heated,
  differentially rotating atmosphere is argued to be a more valid
  explanation.

Title: Modelling A-Type Atmospheres - NLTE Models
Authors: Hubeny, I.; Lanz, T.
Bibcode: 1993ASPC...44...98H
Altcode: 1993IAUCo.138...98H; 1993pvnp.conf...98H
  No abstract at ADS

Title: Spectroscopic Properties of the Nucleus of NGC 6826
Authors: Altner, B.; Heap, S. R.; Hubeny, I.
Bibcode: 1993IAUS..155...86A
Altcode:
  No abstract at ADS

Title: Spectral Diagnoses of Chromospheres and Winds in A-Type Stars
Authors: Lanz, T.; Hubeny, I.
Bibcode: 1993ASPC...44..517L
Altcode: 1993IAUCo.138..517L; 1993pvnp.conf..517L
  No abstract at ADS

Title: Line Blanketed Model Atmospheres for Metal-rich White Dwarfs
Authors: Lanz, T.; Hubeny, I.; Cheng, F. -H.; Horne, K.
Bibcode: 1992AAS...181.5004L
Altcode: 1992BAAS...24.1203L
  In many cases of a close binary system composed of a white dwarf, a
  companion main-sequence or giant star, and an accretion disk around the
  white dwarf, the UV spectrum of the system contains contributions from
  both the white dwarf and the disk. In order to derive information about
  the system from its UV spectrum, the white dwarf atmosphere has to be
  accurately modeled. The chemical composition of the white dwarf is very
  likely to be quite unusual, however, because it may have nearly solar
  composition due to accretion. Due to its high surface gravity, the white
  dwarf's lines are generally very broad, and thus metal line blanketing
  may play a very important role. We have therefore begun a project of
  calculating a grid of non-LTE, fully line-blanketed model atmospheres
  for white dwarfs, for a large range of metal abundances, from zero (pure
  DA) to solar composition. The method is described in a companion paper
  (Hubeny and Lanz) at this meeting. We consider a representative model
  atmosphere with T_eff=15000 K and log g = 8. In this preliminary study,
  only hydrogen and iron (Fe II and Fe III) opacity was considered. The
  models take into account 45815 Fe II and 23059 Fe III lines (all lines
  between the levels with measured energies). As expected, the NLTE
  effects are rather small for this temperature, but the effect of metal
  line blanketing is very important. In particular, we demonstrate how
  the metal line blanketing influences the UV spectrum and the hydrogen
  Lyman and Balmer lines profiles. The work on the project was supported
  in part by the NASA grant No.65 under program NRA 91-OSSA-12.

Title: Non-LTE Line Blanketed Model Atmospheres: Application to
    A-stars
Authors: Hubeny, I.; Lanz, T.
Bibcode: 1992AAS...181.1911H
Altcode: 1992BAAS...24.1152H
  We present a new method for calculating realistic line blanketed model
  atmospheres without the assumption of local thermodynamic equilibrium
  (LTE). The method is based on complete linearization, with the
  following two important modifications with respect to the standard
  variant. i) Instead of dealing separately with individual energy
  levels of a complicated metal species (e.g. Fe II), several levels
  with the same parity and close enough energy are grouped together to
  form a ``superlevel". Transitions between superlevels, the so-called
  ``superlines", are treated by resampling the detailed absorption
  cross-section and forming a partial ``NLTE opacity distribution
  function", which is representable by a relatively small number of
  frequency points (typically 15 - 30 points per superline). ii) The
  radiative rates (together with the heating/cooling rates, and the
  contributions to the rates in other important transitions - e.g. the
  hydrogen and carbon continua) are not fully linearized. However,
  in contrast to the earlier approaches, they are not held fixed. The
  only fixed quantity here is the approximate lambda operator. The new
  method is therefore a hybrid combining the complete linearization
  and the class of modern methods called accelerated lambda iteration
  (ALI). We have contructed several non-LTE model atmospheres for T_eff
  = 10000 K, log g = 4, with H, C I, C II, Mg II, and Fe II treated in
  NLTE. A variable number of Fe II lines, up to 45815 (i.e. all lines
  originating between the levels with measured energies), have been
  included, to form 221 superlines. The most interesting preliminary
  result is that the first 8 Fe II superlevels (about 13000 lines)
  produce most of the total blanketing effect. The work on the project
  was supported by the NASA grant No.65 under program NRA 91-OSSA-12.

Title: Far Ultraviolet Observations of IX Vel with the Hopkins
    Ultraviolet Telescope
Authors: Long, K. S.; Blair, W. P.; Davidsen, A. F.; Hubeny, I.;
   Wade, R. A.
Bibcode: 1992AAS...18110208L
Altcode: 1992BAAS...24.1285L
  No abstract at ADS

Title: Non-LTE Analysis of the Hot Subdwarf: BD 75 325
Authors: Heap, S. R.; Hubeny, I.; Lanz, T.; Altner, B.
Bibcode: 1992AAS...181.5003H
Altcode: 1992BAAS...24.1203H
  No abstract at ADS

Title: Accelerated complete-linearization method for calculating
    NLTE model stellar atmospheres
Authors: Hubeny, I.; Lanz, T.
Bibcode: 1992A&A...262..501H
Altcode:
  Two approaches to accelerating the method of complete linearization
  for calculating NLTE model stellar atmospheres are suggested. The
  first one, the so-called Kantorovich variant of the Newton-Raphson
  method, consists of keeping the Jacobi matrix of the system fixed,
  which allows us to calculate the costly matrix inversions only a few
  times and then keep them fixed during the subsequent computations. The
  second method is an application of the Ng acceleration. Both methods
  are extremely easy to implement with any model atmosphere code based
  on complete linearization. It is demonstrated that both methods, and
  especially their combination, yield a rapidly and globally convergent
  algorithm, which takes 2 to 5 times less computer time, depending
  on the model at hand and the required accuracy, than the ordinary
  complete linearization. Generally, the time gain is more significant
  for more complicated models. The methods were tested for a broad range
  of atmospheric parameters, and in all cases they exhibited similar
  behavior. Ng acceleration applied on the Kantorovich variant thus offers
  a significant improvement of the standard complete-linearization method,
  and may now be used for calculating relatively involved NLTE model
  stellar atmospheres.

Title: Detection of High-Degree Nonradial Pulsations in Gamma Bootis
Authors: Kennelly, E. J.; Yang, S.; Walker, G. A. H.; Hubeny, I.
Bibcode: 1992PASP..104...15K
Altcode:
  The line-profile variations of the rapidly rotating delta Scuti
  star gamma Boo can be explained by high-degree (|m| /= 10) nonradial
  pulsations (NRPs) with an apparent period of Delta t /= 0.047 days. This
  same period was derived from two data sets taken three months apart
  where-in the amplitude increased by 30%. Such high-degree NRP cannot
  explain the apparent reversals previously observed (Auvergne, Le
  Contel &amp; Baglin 1979) for this star in the cores of the hydrogen
  Balmer lines and CaII K line. Our radial-velocity variations can be
  reconciled with their 0.25 day spectroscopic period if an amplitude
  of 1 km s^-1 is adopted, an order of magnitude less than previous
  measurements. We demonstrate that the presence of line-profile
  variations from high-degree modes probably limits the accuracy
  of radial-velocity measurements and may appear as bumps in the
  radial-velocity curve. (SECTION: Stars)

Title: Accelerated Lambda Iteration
Authors: Hubeny, Ivan
Bibcode: 1992LNP...401..375H
Altcode: 1992LNP...401..377H
  Accelerated Lambda Iteration, or ALI, methods are reviewed. An emphasis
  is given to the critical evaluation of various methods, analysing
  their physical and mathematical meaning, and recommending the most
  advantageous methods to interested non-specialists who consider
  applying these methods to solving actual line formation and model
  stellar atmosphere problems.

Title: Accelerated Lambda iteration (review)
Authors: Hubeny, I.
Bibcode: 1992LNP...401..377H
Altcode: 1992aets.conf..377H
  No abstract at ADS

Title: Book-Review - Stellar Atmospheres Beyond Classical Models
Authors: Crivellari, L.; Hubeny, I.; Hummer, D. G.
Bibcode: 1991JBAA..101..364C
Altcode:
  No abstract at ADS

Title: A Nonradial Pulsation Model for the Rapidly Rotating (Delta)
    Scuti Star k^2 Bootis
Authors: Kennelly, E. J.; Walker, G. A. H.; Hubeny, I.
Bibcode: 1991PASP..103.1250K
Altcode:
  A sectorial nonradial pulsation model is used to construct
  theoretical line profiles which mimic the variations for Kappa(2)
  Boo. Synthetic spectra generated with the appropriate Teff and log
  g are used as input. It is found that the data can be reproduced by
  the combination of a high-degree l is approximately equal to 12 mode
  with P(osc) aproximately equal to 0.071 d, and a low-degree mode,
  l is approximately equal to 0-2 with P(osc) approximately equal to
  0.071-0.079 d. The projected rotational velocity (v sin i - 115 +/-5
  km/s) was determined by fitting synthetic line profiles to the observed
  spectra. The velocity amplitude of the high-degree oscillations is
  estimated to be about 3.5 km/s. It is found that the ratio of the
  horizontal and radial pulsation amplitudes is small (about 0.02) and
  consistent with p-mode oscillations. Comparisons are made with models
  invoking starspots, and it is impossible to fit the observations of
  Kappa(2) Boo by a starspot model without assuming unrealistic values
  of radius or equatorial velocity.

Title: A New Look at the Standard Teff = 10000K, log g=4, Non-LTE
    Model Atmosphere
Authors: Lanz, T.; Hubeny, I.; Altner, B.
Bibcode: 1991BAAS...23R1381L
Altcode:
  No abstract at ADS

Title: Can A Disk Explain Beta Lyrae?
Authors: Hubeny, Ivan; Plavec, Mirek J.
Bibcode: 1991AJ....102.1156H
Altcode:
  The Beta Lyrae eclipsing binary system is interpreted in terms of a
  model where the primary, i.e., spectroscopically observable, B star
  transfers matter to a 'canonical' accretion disk surrounding a 'gainer'
  which may be a rather ordinary B0.5 V star. Disk models are calculated
  using the TLUSDISK program. Most of the optical radiation from the
  secondary object is found to come from the disk rim, provided that the
  rate of mass transfer is not much lower than about 0.0001 solar mass
  per year. The rather high disk rim then introduces severe constraints on
  the orbital inclination; these constraints are discussed in detail. It
  is concluded that the disk plays an essentially passive role, and the
  observable radiation from its face is insignificant. A model in which
  most ultraviolet radiation would be coming from the face of the disk
  is found unacceptable both because of these constraints and because
  it would require an unrealistically small radius for the accreting
  star. It is proposed that the bulk of the ultraviolet radiation comes
  from a small unocculted segment of the gainer.

Title: Line Broadening in O-Type Stars: Microturbulence or an Outflow
    Velocity Gradient?
Authors: Hubeny, I.; Altner, B.; Heap, S. R.
Bibcode: 1991BAAS...23.1382H
Altcode:
  No abstract at ADS

Title: First Results from the Goddard High-Resolution Spectrograph:
Evidence for Photospheric Microturbulence in Early O Stars: Are
    Surface Gravities Systematically Underestimated?
Authors: Hubeny, I.; Heap, S. R.; Altner, B.
Bibcode: 1991ApJ...377L..33H
Altcode:
  GHRS spectra of two very hot stars provide evidence for the presence
  of microturbulence in their photospheres. In attempting to reproduce
  the observed spectra, theoretical models have been built in which
  the microturbulence is allowed to modify not only the Doppler line
  widths (classical 'spectroscopic' microturbulence), but also the
  turbulent pressure (thus mimicking a 'physical' turbulence). It is
  found that a corresponding modification of the temperature-pressure
  stratification influences the hydrogen and helium line profiles to the
  extent that the surface gravities of early O stars determined without
  considering microturbulence are too low by 0.1-0.15 dex. Thus, including
  microturbulence would reduce, or resolve completely, a long-standing
  discrepancy between evolutionary and spectroscopic stellar masses.

Title: First Results from the Goddard High-Resolution Spectrograph:
    Spectroscopic Determination of Stellar Parameters of Melnick 42,
    an O3f Star in the Large Magellanic Cloud
Authors: Heap, S. R.; Altner, B.; Ebbets, D.; Hubeny, I.; Hutchings,
   J. B.; Kudritzki, R. P.; Voels, S. A.; Haser, S.; Pauldrach, A.;
   Puls, J.; Butler, K.
Bibcode: 1991ApJ...377L..29H
Altcode:
  GHRS and optical (ESO 3.6 m) observations of the O3f star Melnick 42 in
  the 30 Doradus complex are reported. A first analysis reveals that with
  a luminosity of 2.3 x 10^6^ L_sun_ and a present mass of 100 M_sun_,
  Melnick 42 is one of the most luminous and massive stars known. An
  estimate of abundances indicates that iron and oxygen are very likely
  reduced by a factor of 4 relative to the Sun, whereas carbon is more
  strongly depleted and nitrogen is approximately solar. The terminal
  velocity of the stellar wind is 3000 km s^-1^. The mass-loss rate is 4
  x 10^-6^ M_sun_ yr^-1^, with a large uncertainty. The excellent quality
  GHRS spectrum taken in a crowded region of the LMC demonstrates the
  superiority of the HST for quantitative ultraviolet spectroscopy of
  hot stars in other galaxies.

Title: Non--LTE Analysis of the Ofpe/WN9 Star HDE 269227 (R84)
Authors: Schmutz, Werner; Leitherer, Claus; Hubeny, Ivan; Vogel,
   Manfred; Hamann, Wolf-Rainer; Wessolowski, Ulf
Bibcode: 1991ApJ...372..664S
Altcode:
  The paper presents the results of a spectral analysis of the Ofpe/WN9
  star HD 269227 (R84), which assumes a spherically expanding atmosphere
  to find solutions for equations of radiative transfer. The spectra of
  hydrogen and helium were predicted with a non-LTE model. Six stellar
  parameters were determined for R84. The shape of the velocity law is
  empirically found, since it can be probed from the terminal velocity
  of the wind. The six stellar parameters are further employed in a
  hydrodynamic model where stellar wind is assumed to be directed by
  radiation pressure, duplicating the mass-loss rate and the terminal
  wind velocity. The velocity laws found by computation and analysis
  are found to agree, supporting the theory of radiation-driven stellar
  wind. R84 is surmised to be a post-red supergiant which lost half of
  its initial mass, possibly during the red-supergiant phase. This mass
  loss is also suggested by its spectroscopic similarity to S Doradus.

Title: Stellar atmospheres. Beyond classical models
Authors: Crivellari, Lucio; Hubeny, I.; Hummer, D. G.
Bibcode: 1991ASIC..341.....C
Altcode: 1991QB809.N38......; 1991sabc.conf.....C
  No abstract at ADS

Title: Model Atmospheres for Accretion Disks.
Authors: Hubeny, I.
Bibcode: 1991sepa.conf..227H
Altcode: 1991IAUCo.129..227H
  No abstract at ADS

Title: Computer Codes for Stellar Atmospheric Modeling
Authors: Hummer, D. G.; Hubeny, I.
Bibcode: 1991ASIC..341..119H
Altcode: 1991sabc.conf..119H
  No abstract at ADS

Title: Stringent Limits on the Ionized Mass Loss from A and F Dwarfs
Authors: Brown, Alexander; Veale, Anthony; Judge, Philip; Bookbinder,
   Jay A.; Hubeny, Ivan
Bibcode: 1990ApJ...361..220B
Altcode:
  Following the suggestion of Willson et al. (1987) that A- and
  F-type main-sequence stars might undergo significant mass loss due to
  pulsationally driven winds, upper limits to the ionized mass loss from A
  and F dwarfs have been obtained using VLA observations. These stringent
  upper limits show that the level of ionized mass loss would have at
  most only a small effect on stellar evolution. Radiative-equilibrium
  atmospheric and wind models for early A dwarfs indicate that it is
  highly likely that a wind flowing from such stars would be significantly
  ionized. In addition, late A and early F dwarfs exhibit chromospheric
  emission indicative of significant nonradiative heating. The present
  mass-loss limits are thus representative of the total mass-loss rates
  for these stars. It is concluded that A and F dwarfs are not losing
  sufficient mass to cause A dwarfs to evolve into G dwarfs.

Title: Properties of the central star of NGC 6826
Authors: Heap, S.; Altner, B.; Hubeny, I.; Bohannan, B.
Bibcode: 1990ESASP.310..397H
Altcode: 1990eaia.conf..397H
  No abstract at ADS

Title: Vertical Structure of Accretion Disks: A Simplified Analytical
    Model
Authors: Hubeny, I.
Bibcode: 1990ApJ...351..632H
Altcode:
  A simplified model of the vertical structure of accretion disks
  is derived. Analytical expressions for the temperature and density
  structure, which represent a generalization of the gray model long known
  in the theory of classical stellar atmospheres, are presented. The
  formalism naturally explains similarities and differences between
  the structure of a disk and a stellar atmosphere. In particular, the
  influence of viscous dissipation and external irradiation of the disk
  by the central star, as well as of the finite optical thickness of the
  disk, may be easily accounted for and explained by the present model.

Title: Spectroscopic Determinations of the Properties of Planetary
    Nuclei
Authors: Heap, S. R.; Altner, B.; Hubeny, I.; Bohannan, B.
Bibcode: 1990BAAS...22..848H
Altcode:
  No abstract at ADS

Title: Model atmospheres of hot stars: a rescaling method.
Authors: Hubeny, Ivan
Bibcode: 1990ASPC....7...93H
Altcode: 1990phls.work...93H
  A simple method is suggested that overcomes convergence difficulties
  encountered in calculating non-LTE model atmospheres of hot stars. The
  method is based on a rescaling of the radiative as well as heating
  / cooling rates by removing analytically the overwhelming number of
  scatterings and retaining only terms of the order of thermal absorptions
  and emissions.

Title: Mass Loss Upper Limits for a and F Dwarfs
Authors: Brown, A.; Veale, A.; Judge, P.; Bookbinder, J.; Hubeny, I.
Bibcode: 1990ASPC....9..183B
Altcode: 1990csss....6..183B
  The upper limits of the ionized mass losses of A- and F-type main
  sequence stars are obtained with the VLA to investigate the theory that
  pulsationally driven winds contribute to substantial mass loss in the
  stars. The upper limits are found to be at least one order of magnitude
  lower than the mass-loss loci proposed by Willson et al. (1987). Because
  any wind flowing from the stars should be detectable, the notion that
  A dwarfs are evolving into G dwarfs cannot be supported by the amount
  of mass that A and F dwarfs are shown to be losing.

Title: Approximate Formulation of Redistribution in the LY alpha ,
    LY beta , H alpha System
Authors: Cooper, J.; Ballagh, R. J.; Hubeny, I.
Bibcode: 1989ApJ...344..949C
Altcode:
  Simple approximate formulas are given for the coupled redistribution of
  Ly-alpha, Ly-beta, and H-alpha, by using well-defined approximations to
  an essentially exact formulation. These formulas incorporate all the
  essential physics including Raman scattering, lower state radiative
  decay, and correlated terms representing emission during a collision
  which must be retained in order that the emission coefficients are
  properly behaved in the line wings. Approximate expressions for
  the appropriate line broadening parameters are collected. Finally,
  practical expressions for the source functions are given. These are
  formulated through newly introduced nonimpact redistribution functions,
  which are shown to be reasonably approximated by existing (ordinary
  and generalized) redistribution functions.

Title: Theoretical Modelling of Algol Disks
Authors: Hubeny, I.
Bibcode: 1989SSRv...50..117H
Altcode: 1989IAUCo.107..117H
  A brief review of various theoretical approaches to model accretion
  disks is presented. Emphasis is given to models that determine
  self-consistently the structure of a disk together with the radiation
  field. It is argued that a proper treatment of the vertical structure
  is essential for calculating theoretical spectra to be compared
  with observations. In particular, it is shown that hot layers above
  an accretion disk (sometimes called disk “chromospheres” or
  “coronae”), whose presence is indicated by recent UV observations
  of strong emission lines of highly ionized species, may be explained
  using simple energy balance arguments.

Title: Redistribution in astrophysically important hydrogen lines
Authors: Cooper, J.; Ballagh, R. J.; Hubeny, I.
Bibcode: 1989STIN...8924251C
Altcode:
  Under typical solar chromospheric conditions for hydrogen radiators,
  strong collisions due to both electrons and ions are well separated in
  time, so that a binary collision theory for collisional redistribution
  is applicable. However, a simple impact approximation may not be
  used, but rather a unified type theory is required in which frequency
  dependent line shape parameters are used to describe both impact and
  quasi-static regions of the spectrum. In addition, correlated terms
  which describe absorption and emission during a collision are important,
  and, in fact, without correlated terms describing both transfer of
  excitation and emission during the same collision unphysical predictions
  (such as negative intensities) would be obtained. In this paper theory
  is specifically developed for the coupled Lyman-alpha, Lyman-beta,
  Hydrogen-alpha system, and equations of statistical equilibrium and
  absorption and emission coefficients are given. All correlated events
  are examined and emission during a collision is found to be important
  in the line wings. Stimulated emission and absorption is also included
  within a broadband approximation. The major approximation is to ignore
  lower state interaction. It is found that for Lyman-beta Raman-coupling
  with Hydrogen-alpha occurs and the overall scattering of radiation in
  the line wings is mostly coherent. In contrast, for Hydrogen-alpha,
  incoherent redistribution due to lower state radiative decay (which
  occurs even in the absence of collisions) is found to dominate
  the coherent scattering. Finally, in the Lyman series the dominant
  incoherent contribution is associated with cascade transitions and
  inelastic collisions between different principal quantum states.

Title: On the Interpretation of Emission Wings of Balmer Lines
    in Lbv's
Authors: Hubeny, I.; Leitherer, C.
Bibcode: 1989ASSL..157..283H
Altcode: 1989plbv.coll..283H; 1989IAUCo.113..283H
  No abstract at ADS

Title: Influence of Radiative Transfer on the Vertical Structure of
    Accretion Disks
Authors: Hubeny, I.
Bibcode: 1989ASIC..290..445H
Altcode: 1989tad..conf..445H
  No abstract at ADS

Title: On the Interpretation of Emission Wings of Balmer Lines in
    Luminous Blue Variables
Authors: Hubeny, Ivan; Leitherer, Claus
Bibcode: 1989PASP..101..114H
Altcode:
  H-alpha line profiles calculated with plane-parallel, hydrostatic
  non-LTE model atmospheres are discussed. In the lowest log g models
  the profiles show extended emission wings. Qualitatively, these wings
  are similar to the extended wings generated by electron scattering of
  line photons in the stellar wind. It is proposed that the line wings
  observed in luminous blue variables may be due to a combination of the
  non-LTE effect discussed here and the traditional scattering mechanism.

Title: Radiation transfer with partial frequency redistribution and
    generalized redistribution functions.
Authors: Hubeny, I.
Bibcode: 1989fapi.conf..242H
Altcode:
  The author attempted to analyse the available astrophysical partial
  redistribution studies. He introduced the term quasi-Markovian,
  classical view, where the basic physical concepts of the current
  astrophysical approach are summarized. Its physical uncertainties, and
  even inconsistencies, are discussed in detail. The quasi-Markovian,
  classical treatment has been used to generalize the Oxenius
  (1965) approach. The reformulation of the Oxenius' approach, in the
  two-level-atom case, to a form similar to that of Milkey and Mihalas
  (1973) and Heasley and Kneer (1976) showed, that both formulations yield
  almost identical results. Using the same approach as in reformulating
  the two-level-atom case, the author derived a suitable form of the
  emission coefficient in the case of the multilevel atom. Comparing
  its form to that following from a heuristic derivation, two points
  appeared to be different.

Title: A computer program for calculating non-LTE model stellar
    atmospheres
Authors: Hubeny, I.
Bibcode: 1988CoPhC..52..103H
Altcode:
  The program calculates model stellar atmospheres, assuming
  plane-parallel, horizontally homogeneous atmosphere in radiative
  and hydrostatic equilibrium, and allowing for departures from local
  thermodynamic equilibrium (LTE) for a set of occupation numbers of
  selected atomic and ionic energy levels. The program is very flexible
  as to the choice of chemical.

Title: Scattering of Polarized Light in Spectral Lines with Partial
Frequency Redistribution: General Redistribution Matrix
Authors: Domke, H.; Hubeny, I.
Bibcode: 1988ApJ...334..527D
Altcode:
  The redistribution matrix for resonance scattering of arbitrarily
  polarized light, described by a vector of Stokes parameters, is derived
  assuming that the ground state is isotropic. When specified in the
  atomic rest frame, the redistribution matrix is found to be composed
  of several terms with individually separate frequency and angular
  dependence. The laboratory frame redistribution matrix exhibits an
  analogous structure, but the angular and frequency dependences are
  intermingled. Two possibilities for treating the angular dependence
  in practical applications are considered: an expansion in a series of
  Legendre polynomials and an azimuthal expansion. Finally, the concept
  of aximuthally average redistribution matrix is examined, and explicit
  expressions for resonance lines are given.

Title: Non-LTE Effects in the Atmospheres of F-Type Supergiants -
    Part Two - Analysis of NAI Lines (The Method of Computations)
Authors: Boyarchuk, A. A.; Hubeny, I.; Kubat, J.; Lyubimkov, L. S.;
   Sakhibullin, N. A.
Bibcode: 1988Afz....28..335B
Altcode:
  The method of non-LTE computations of Na I lines is described. The
  calculations were aimed to reveal a probable connection between the
  observed sodium overabundance in F-K supergiants and departures from LTE
  in Na I lines is used for the analysis. Special attention is given to
  subordinate lines, therefore the accepted model of Na I atom includes
  19 levels instead of 7-9 levels as in the previous investigations
  [3-6]. A list of stars for which the lines are computed compiles six
  F-supergiants and three dwarfs (table 1). The data on the studied Na
  I lines are adduced (table 2).

Title: Non-LTE effects in the atmospheres of F-type
    supergiants. III. Analysis of NA I lines (results of computations).
Authors: Boyarchuk, A. A.; Hubeny, I.; Kubat, J.; Lyubimkov, L. S.;
   Sakhibullin, N. A.
Bibcode: 1988Afz....28..343B
Altcode: 1988Afz....28..342B
  Non-LTE populations of the Na I atomic levels are calculated for six
  F-supergiants and three dwarfs. The profiles and equivalent widths
  W_lambda of some Na I lines of interest are computed. It is shown
  thatordinary changes in widths W_lambda of subrodinate lines relative
  to LTE are not more than 10% and they do not lead to appreciable
  correction in the sodium abundance (corrections are less than 0.1
  dex). Only for most massive supergiants with log g ~ 0 the derived
  abundance might be reduced by about 0.2 dex. The Na overabundance found
  for yellow supergiants from LTE analysis is confirmed. The correlation
  between the Na excess and log g obtained earlier is confirmed, too;
  probably it is a result of the analogous correlation between the Na
  excess and masses of supergiants (fig.3). It is noticed that the modern
  calculations confirm the supposition that the source of enhanced sodium
  abundance is the NeNa-cycle.

Title: NLTE Analysis of the Luminous Blue Variable R71
Authors: Leitherer, C.; Schmutz, W.; Hubeny, I.
Bibcode: 1988BAAS...20.1012L
Altcode:
  No abstract at ADS

Title: Overabundance of Sodium in the Atmospheres of Massive
    Supergiants as a Possible Manifestation of Nena Cycle
Authors: Boyarchuk, A. A.; Denisenkov, P. A.; Hubeny, I.; Ivanov,
   V. V.; Kubat, I.; Lyubimkov, L. S.; Sakhibullin, N. A.
Bibcode: 1988LNP...305...94B
Altcode: 1988IAUCo.108...94B; 1988adse.conf...94B
  No abstract at ADS

Title: Probabilistic interpretation of radiative transfer. I -
    The square root of epsilon law. II - Rybicki equation
Authors: Hubeny, I.
Bibcode: 1987A&A...185..332H
Altcode:
  A simple physical explanation is given for the standard problem of line
  formation theory, stating that the source function at the surface
  is given by (the square root of epsilon)B. The present approach
  assumes that the frequency averaged mean intensity of radiation
  and the source function, at a given depth, are proportional to the
  probability of ultimate thermalization of a photon emitted or absorbed
  at this depth. In the second part, a physical explanation of the Rybcki
  (1977) generalization of the square root of epsilon law is given to all
  depths of an atmosphere. Various probabilistic concepts such as the
  frequency-dependent and angle-dependent thermalization probabilities
  are introduced.

Title: Probabilistic Interpretation of Radiative Transfer - Part Two -
    Rybicki Equation
Authors: Hubeny, I.
Bibcode: 1987A&A...185..336H
Altcode:
  By extending the approach developed in the previous part of this paper,
  we present a physical explanation of the Rybicki generalization of
  the √ ɛ-law to all depths of an atmosphere. To this end, various
  probabilistic concepts, in particular the frequency- and angle-dependent
  thermalization probabilities, are introduced, and relations between
  them and the specific intensity of radiation are studied in detail.

Title: Absorption and emission line profile coefficients of multilevel
    atoms - IV. Velocity-averaged generalized redistribution functions
    for three-photon processes.
Authors: Hubeny, I.; Oxenius, J.
Bibcode: 1987JQSRT..37..397H
Altcode:
  The atomic generalized redistribution functions for three-photon
  processes, derived in the previous paper of this series, are formulated
  in terms of linear superpositions of newly introduced auxiliary
  functions q<SUB>I</SUB> - q<SUB>VI</SUB>, thus extending the traditional
  formalism of redistribution functions for two-photon processes. The
  corresponding velocity-averaged laboratory functions Q<SUB>I</SUB> -
  Q<SUB>VI</SUB> of these auxiliary functions are derived in both their
  angle-dependent and angle-averaged forms. Since the expressions found
  for Q<SUB>I</SUB> - Q<SUB>VI</SUB> are quite complicated, the so-called
  disentangled approximation is employed that uses the representative
  values of the generalized redistribution function at an orthogonal
  triad of photon directions rather than the angle-averaged function
  itself. This approximation yields relatively simple expressions which
  can be used in radiative transfer calculations.

Title: Absorption and emission line profile coefficients of
    multilevel atoms - III. Generalized atomic redistribution functions
    for three-photon processes.
Authors: Hubeny, I.; Oxenius, J.
Bibcode: 1987JQSRT..37...65H
Altcode:
  A previously published semiclassical formulation of the atomic line
  profile coefficients in terms of generalized redistribution functions
  is made more explicit by deriving atomic redistribution functions for
  three-photon processes. Quantum mechanical calculations are carried
  out for a general three-photon process corresponding to the atomic
  transition sequence i → j → k → f, for nondegenerate states
  i, j, k, f and within the framework of the impact approximation. For
  comparison, analogous calculations are also performed using the substate
  (Weisskopf-Woolley) picture. It is found that the quantum mechanical
  and the substate forms of generalized redistribution functions agree
  in the limit of no collisions, whereas in the presence of collisions
  they agree only if level interference phenomena of the collisional
  line broadening are negligible. The physical assumptions underlying
  the substate picture are discussed in detail.

Title: How Strong is the Evidence of Superionization and Large Mass
    Outflows in B/Be Stars? 2. The C IV and SI IV Lines in the UV Spectra
    of V 767 Cen, ο And, Θ CrB, λ Eri, and 59 CYG
Authors: Hubeny, I.; Harmanec, P.; Stefl, S.
Bibcode: 1986BAICz..37..370H
Altcode:
  The theoretical spectra in the neighborhood of the C IV and Si IV
  resonance lines have been compared with the published observed spectra
  of five Be stars, V 767 Cen, omicron And, Theta CrB, Lambda Eri,
  and 59 Cyg. It is shown that the published determinations of large
  outflow velocities evidenced by a violet asymmetry of the C IV and
  Si IV lines, as well as the reports of superionization based on the
  observations of the C IV and Si IV lines, should be reconsidered in
  view of considerable line blending effects. In general, it is suggested
  that many of the puzzling features observed in the UV spectra of B/Be
  stars may be explained in terms of heavy blending of lines originating
  in the photospheres and/or subionized, slowly rotating envelopes of
  the underlying stars.

Title: Redistribution of Radiation in the Presence of
    Velocity-changing Collisions
Authors: Hubeny, I.; Cooper, J.
Bibcode: 1986ApJ...305..852H
Altcode:
  Starting with the recent work of Cooper et al., a suitable form
  of the normalized redistribution function relevant for a treatment
  of redistribution in the presence of velocity-changing collisions
  is presented. Attention is devoted to provide practical estimates
  of the ratio between the usual line-broadening parameters and the
  velocity-changing rate. It is shown that for virtually all cases of
  astrophysical interest the effect of velocity-changing collisions is
  quite negligible.

Title: Models and theoretical spectra of accretion discs in dwarf
    novae.
Authors: Kriz, S.; Hubeny, I.
Bibcode: 1986BAICz..37..129K
Altcode:
  Attention is given to a new technique for modelling dwarf novae
  accretion disks which permits the consistent determination of
  disk structure together with the radiation field. A cylindrically
  symmetric disk is divided into a set of concentric rings, each of them
  behaving independently, like a plane-parallel radiating slab. The
  vertical structure of each ring is determined by the joint solution
  of hydrostatic equilibrium, energy balance and radiative transfer
  equations. Numerical computations were carried out for a stationary
  disk with a central star having a mass equal to 1 solar mass and a
  radius equal to 5 x 10 to the 8th cm; the mass flux through the disk
  is taken to be 10 to the -8th, 10 to the -10th, and 10 to the -11th
  the solar mass per yr. Comparison of the theoretical radiative flux
  distribution with the observed distribution of the white dwarf WX Hyi
  reveals that the quiescent state of Wx Hyi corresponds to a mass flux
  of about 10 to the -11th the solar mass per yr.

Title: Comments on "The angle-dependent redistribution functions
    R<SUB>III</SUB> and R<SUB>IV</SUB>" by S. J. McKenna.
Authors: Hubeny, I.; Heinzel, P.
Bibcode: 1986Ap&SS.119..409H
Altcode:
  It is shown that the complicated form of the line absorption probability
  function for scattering in subordinate lines, derived by McKenna (1984),
  is an artifact of adopting a mathematically inconvenient expression
  for the corresponding redistribution function. It is demonstrated that
  the absorption probability must be given by the Voigt function.

Title: Model Atmospheres and Radiative Transfer in Chemically Peculiar
Stars: Interpretational Significance of Non-Lte (invited Review)
Authors: Hubeny, I.
Bibcode: 1986ASSL..125...57H
Altcode: 1986umss.conf...57H; 1986umss.proc...57H; 1986IAUCo..90...57H
  Local-thermodynamic equilibrium (LTE) and more general non-TEL (NLTE)
  approaches are investigated in the study of chemically peculiar (CP)
  stars, and it is found that while LTE model atmospheres appear to be
  a satisfactory diagnostic tool for continua of A and late B stars,
  more detailed observations and/or the far UV region require an NLTE
  treatment. Detailed comparison of the observed and predicted profiles of
  resonance lines, in addition to an account for partial redistribution
  effects through calculation of the NLTE theoretical profiles, are
  suggested for accurate abundance determinations. Line blanketing is
  also considered, and it is found that some important lines and continua
  must be treated in NLTE, while others may be treated in LTE.

Title: Methods in radiative transfer
Authors: Hubený, Ivan
Bibcode: 1985Ap&SS.115..199H
Altcode:
  No abstract at ADS

Title: Book-Review - Methods in Radiative Transfer
Authors: Kalkofen, W.; Hubeny, I.
Bibcode: 1985Ap&SS.115..199K
Altcode:
  No abstract at ADS

Title: How Strong is the Evidence of Superionization and Large Mass
    Outflows in B/Be Stars?
Authors: Hubeny, I.; Stefl, S.; Harmanec, P.
Bibcode: 1985BAICz..36..214H
Altcode:
  Consideration is given to the spectroscopic diagnostics of
  superionization and large mass outflows in B stars according to the UV
  resonance lines of C IV, SiIV, and N V. The effects of line blending in
  the vicinity of these lines were estimated by means of a theoretical
  spectral grid which was computed for main sequence and supergiant
  model atmospheres in the range of effective temperatures 8000-40,000
  K. It is argued that the supergiant spectra may simulate the spectra
  of Be envelopes well enough to serve as a model. The results are used
  to demonstrate the observability of shell lines in the Be envelope
  in the ultraviolet spectrum, even when they are not observable in
  optical spectra.

Title: A modified Rybicki method and the partial coherent scattering
    approximation
Authors: Hubeny, I.
Bibcode: 1985A&A...145..461H
Altcode:
  It is the purpose of the paper to demonstrate that it is possible
  to combine the advantages of the partial coherent scattering (PCS)
  approximation with the favorable numerical properties of the Rybicki
  method. To accomplish this goal, the author carries out an analysis
  which indicates the way of accounting for Doppler diffusion within the
  framework of the PCS approximation. The essence of the present method
  consists in considering the frequency that sets the boundary between
  the complete redistribution core region and the coherent wing region to
  be depth-dependent. From the mathematical point of view, the present
  modification is purely at the computational level and thus retains
  the ease of formulation and programming of the original Rybicki method.

Title: Non-LTE line transfer with partial redistribution. II -
    an equivalent-two-level-atom approach
Authors: Hubeny, I.
Bibcode: 1985BAICz..36....1H
Altcode:
  A formulation of equations for radiative transfer in a gas of
  multilevel atoms, taking into account recent developments of theoretical
  description, is presented. It is shown that for a simple case where one
  chosen transition is allowed to depart from complete redistribution,
  the global multilevel problem may be solved by suitably modified
  complete-redistribution numerical techniques. In particular, the author
  has formulated a modification of the equivalent-two-level-atom approach
  that enables a multilevel transfer to be solved by a simple iteration
  scheme. Various approximate forms of the line source function are
  also discussed.

Title: General aspects of partial redistribution and its astrophysical
    importance.
Authors: Hubeny, I.
Bibcode: 1985ASIC..152...27H
Altcode: 1985pssl.proc...27H
  A review is given of new developments in the theory of partial
  redistribution in radiative transfer problems. Emphasis is on the
  transfer of unpolarized radiation in plane parallel static media,
  but effects of velocity fields and of geometrical structure are also
  briefly discussed. Applications to solar and stellar spectral line
  formation are outlined.

Title: How strong is the evidence of superionization and large mass
    outflowsin B/Be stars?
Authors: Hubeny, I.; Stefl, S.; Harmanec, P.
Bibcode: 1985BIEBe..11....9H
Altcode:
  No abstract at ADS

Title: Partial redistribution interlocking in the solar chromosphere.
Authors: Heinzel, P.; Hubeny, I.
Bibcode: 1985ASIC..152..137H
Altcode: 1985pssl.proc..137H
  Starting with the model of a quiet solar chromosphere, the authors
  have calculated the relative probabilities of radiative and natural
  population of the second and third hydrogen levels, pertinent to
  various population processes. The analysis indicates that, while the Lα
  line is formed by resonance scattering between the first two levels,
  the third hydrogen level, from which Lβ and Hα are generated,
  is populated partly by direct photoexcitation 1→3 (about 55%),
  and partly by two-photon absorption 1→2→3 (about 45%).

Title: A modified Rybicki method with partial redistribution.
Authors: Hubený, I.
Bibcode: 1985ASIC..152..101F
Altcode: 1985pssl.proc..101F; 1985pssl.proc..109H
  The mathematical expression of the emission profile Ψ<SUB>ν</SUB>
  is given in the case of a two-level atom plus continuum: the result
  is that Ψ<SUB>ν</SUB> is independent of populations and abundances,
  depending only on T<SUB>e</SUB>, N<SUB>e</SUB> and J<SUB>ν</SUB>.

Title: A modified Rybicki method with partial redistribution.
Authors: Hubeny, I.
Bibcode: 1985ASIC..152..109H
Altcode:
  A new approximate numerical method is presented that retains the basic
  computational advantages of the Rybicki method while still being
  capable of handling partial redistribution transfer problems. The
  crucial point of this method is to consider the frequency which
  separates the complete redistribution core region from the coherent
  wing region, to be depth-dependent. The present method yields excellent
  agreement with exact calculations and gives much better results than
  any depth-independent version of the partial coherent scattering
  approximation.

Title: Non-coherent scattering in subordinate lines - V. Solutions
    of the transfer problem.
Authors: Hubeny, I.; Heinzel, P.
Bibcode: 1984JQSRT..32..159H
Altcode:
  Redistribution functions are defined for resonance scattering and shown
  to be of use in astrophysics problems. An isotropic approximation is
  included in a definition of a two-level atom line source function and
  the redistribution function is angle-averaged for scattered photons,
  which are treated as negative absorption. Various redistribution
  functions, either partial or complete, are then applied to slab,
  isothermal, finite, and semi-infinite atmospheres for a given absorption
  profile and the line source function to examine the resulting transfer
  functions. The ratios of the upper/lower level damping are found to
  have a significant impact on the type of redistribution expected. An
  approximate form of the redistribution function is determined as
  adequate for calculating line profiles, especially in the wings.

Title: The far-ultraviolet energy distribution of Sirius B from
    Voyager 2.
Authors: Holberg, J. B.; Wesemael, F.; Hubeny, I.
Bibcode: 1984ApJ...280..679H
Altcode:
  Observations of Sirius obtained with the Voyager 2 ultraviolet
  spectrometer clearly reveal the presence of flux from the white dwarf
  Sirius B at wavelengths between 950 and 1100 A. These observations are
  in good agreement with all previous ultraviolet observations of Sirius
  B, and in particular with the IUE observations of Boehm-Vitense,
  Dettmann, and Kapranidis. A joint analysis of the Voyager 2 and
  IUE observations yields a temperature range of 26,000-28,000 K. A
  reexamination of current ultraviolet, visible, and X-ray observations
  produces good general agreement, but no single, mutually consistent,
  temperature for Sirius B. The Voyager 2 observations can be used to
  place a firm upper limit of 28,000 K on the temperature of Sirius B.

Title: On the line profile coefficient for stimulated emission
Authors: Cooper, J.; Hubeny, I.; Oxenius, J.
Bibcode: 1983A&A...127..224C
Altcode:
  It is pointed out that the line profile coefficients for spontaneous and
  stimulated emission are identical in low-intensity radiation fields. In
  more intense radiation fields, however, the stimulated emission profiles
  in the radiative transfer equation and in the rate equations for the
  atomic level populations may differ from each other, owing to their
  different physical nature. A seeming discrepancy between the stimulated
  emission profiles of the usual semi-classical approach and a recent
  quantum mechanical approach by Cooper et al. (1982), which should
  also be valid for intense "broadband" fields, is discussed and shown
  to have negligible consequences for low-intensity radiation fields.

Title: Non-coherent scattering in subordinate lines:
    IV. Angle-averaged redistribution functions.
Authors: Heinzel, P.; Hubený, I.
Bibcode: 1983JQSRT..30...77H
Altcode:
  It is demonstrated that a simple Gaussian quadrature over the
  scattering angles provides a sufficiently accurate and stable method
  for evaluating all the angle-averaged redistribution functions
  R<SUB>i</SUB>(xarcmin,x) (i = I-V). The authors display graphically
  the functions R<SUB>II,III,V</SUB> and discuss in detail the behaviour
  of the newly calculated redistribution R<SUB>V</SUB>(xarcmin,x).

Title: Voyager 2 far-ultraviolet observations of Sirius B.
Authors: Holberg, J. B.; Wesemael, F.; Hubeny, I.; Forrester, W. T.;
   Barry, D. C.
Bibcode: 1983BAAS...15..879H
Altcode:
  No abstract at ADS

Title: Absorption and emission line profile coefficients of multilevel
    atoms - II. Velocity-averaged profile coefficients.
Authors: Hubený, I.; Oxenius, J.; Simonneau, E.
Bibcode: 1983JQSRT..29..495H
Altcode:
  Starting from the atomic profile coefficients of a multilevel atom
  derived in the previous first part of this paper, the authors consider
  the velocity-averaged line profile coefficients appearing in the
  radiative transfer equation for the important special case that the
  velocity distribution of atoms in the ground state is Maxwellian and
  that the streaming of excited atoms is negligible.

Title: Absorption and emission line profile coefficients of multilevel
    atoms - I. Atomic profile coefficients.
Authors: Hubeny, I.; Oxenius, J.; Simonneau, E.
Bibcode: 1983JQSRT..29..477H
Altcode:
  The line profile coefficients for absorption and emission appearing
  in the radiative transfer equation are formulated in terms of atomic
  line profile coefficients and velocity distribution functions.

Title: Voyager 2 far-ultraviolet observations of Sirius B.
Authors: Holberg, J. B.; Wesemael, F.; Hubený, I.; Forrester, W. T.;
   Barry, D. C.
Bibcode: 1983BAAS...15Q.879H
Altcode:
  No abstract at ADS

Title: Non-coherent scattering in subordinate lines: III. Generalized
    redistribution functions.
Authors: Hubený, I.
Bibcode: 1982JQSRT..27..593H
Altcode:
  No abstract at ADS

Title: Non-coherent scattering in subordinate lines: II. Collisional
    redistribution.
Authors: Heinzel, P.; Hubený, I.
Bibcode: 1982JQSRT..27....1H
Altcode:
  No abstract at ADS

Title: On the importance of convective transport of excited atoms
    in stellar atmospheres
Authors: Hubeny, I.
Bibcode: 1981A&A...100..314H
Altcode:
  The question of the importance of the convective or diffusion transport
  of excited atoms dur to their density gradients generated by non-LTE
  line transfer, is reconsidered. It is shown that such kinetic effects
  are practically never important under stellar atmospheric conditions,
  contrary to the previous study of Oxenius (1979). This different
  conclusion follows from the discussion of an explicit form of the
  coupled set of kinetic equation for excited atoms and the radiative
  transfer equation, as well as from the proper parameterization of the
  physical state of stellar atmospheres.

Title: Non-LTE analysis of the ultraviolet spectrum of A type
    stars. II Theoretical considerations and interpretation of the VEGA
    Lyman-alpha region
Authors: Hubeny, I.
Bibcode: 1981A&A....98...96H
Altcode:
  Main-sequence early A-type model stellar atmospheres are
  investigated. The intention is to clarify the interpretational
  significance of the various assumptions used in calculating model
  stellar atmospheres and the emergent radiative flux. Several non-LTE
  model atmospheres in radiative and hydrostatic equilibria for early
  A-type stars are constructed. The effects of departures from LTE
  for early A-type stars are found to be of primary importance for
  the far ultraviolet spectrum and significant in the ultraviolet
  spectrum. It is also found that the properties of the computed NLTE
  model atmospheres are sensitive to the assumptions of the treatment
  of the far ultraviolet opacity sources. A qualitative estimate reveals
  that the run of physical parameters of a realistic NLTE line-blanketed
  model atmosphere is bracketed by that of the NLTE model without
  line-blanketing from the one side and that of the LTE line-blanketed
  model from the other side. It is noted that at present there does not
  exist any theoretical model yielding a 'correct' ultraviolet flux,
  particularly that below 1520 A for A stars.

Title: A computer program for calculating non-LTE model stellar
    atmospheres.
Authors: Hubený, I.
Bibcode: 1981PAICz..57...32H
Altcode:
  No abstract at ADS

Title: Radiative transfer and model atmospheres of A and Ap stars.
Authors: Hubeny, I.
Bibcode: 1981SoSAO..32...23H
Altcode:
  No abstract at ADS

Title: Stellar spectra and their interpretation. Proceedings of
    the First Conference of the Subcommission No. 2 of the Committee
    of Multilateral Cooperation of the Academies of Sciences of the
    Socialist Countries "Physics and the Evolution of Stars", held at
    Brno, Czechoslovakia, June 8 - 12, 1981.
Authors: Hubený, I.; Onderlička, B.
Bibcode: 1981PAICz..57.....H
Altcode:
  No abstract at ADS

Title: Book-Review - Stellar Turbulence - I.A.U. Colloquium 51 -
    London Ontario, Canada - 1979AUG27-30
Authors: Gray, D. F.; Linsky, J. L.; Hubeny, I.
Bibcode: 1981BAICz..32..255G
Altcode:
  No abstract at ADS

Title: Non-LTE Line Transfer with Partial Redistribution. I. General
    Emission Profile
Authors: Hubený, I.
Bibcode: 1981BAICz..32..271H
Altcode:
  No abstract at ADS

Title: Stellar Spectra and Their Interpretation. 1st conference of
    the Subcommission No. 2
Authors: Hubeny, I.; Onderlicka, B.
Bibcode: 1981sspi.book.....H
Altcode:
  No abstract at ADS

Title: Line blanketing in the Lyman-alpha wings
Authors: Hubeny, I.
Bibcode: 1981LIACo..23..373H
Altcode: 1981cpsu.conf..373H
  A schematic study of the formation of lines in the Lyman-alpha wings
  in A and late B stars is presented. It is demonstrated that lines
  situated in the Lyman-alpha wings have very complex profiles, and in
  several cases they can appear strongly in emission. fitting the observed
  fluxes to those predicted by the model atmosphere calculation of Kurucz
  (1979). This emission tends to increase with increasing abundance and
  with decreasing distance from the Lyman-alpha center. It is tentatively
  suggested that this effect can explain the anomalous brightness
  variations in the Lyman-alpha wings of alpha-2 CVn and similar stars.

Title: The effect of Lyman-alpha on the non-LTE model atmospheres
    of A type stars
Authors: Hubeny, I.
Bibcode: 1980A&A....86..225H
Altcode:
  The importance of the Ly-alpha line in the calculation of non-LTE model
  atmospheres of A type stars is pointed out. It is shown that due to
  the specific conditions in the atmospheres of A type stars, even very
  far wings of Ly-alpha are important and produce considerable effects
  upon the atmospheric structure. The importance of a proper treatment
  of Stark broadening as well as redistribution in the Ly-alpha line is
  briefly discussed.

Title: Multidimensional radiative transfer in ultraviolet resonance
    lines of the chromospheric flash spectrum
Authors: Hubený, I.
Bibcode: 1976CoSka...6..383H
Altcode:
  No abstract at ADS

Title: Multidimensional radiative transfer in ultraviolet resonance
    lines of the chromospheric flash spectrum.
Authors: Hubený, I.
Bibcode: 1976str..book..383H
Altcode:
  No abstract at ADS

Title: Improved Complete-Linearization Method for the Solution of
    the Non-LTE Line Transfer Problem
Authors: Hubeny, I.
Bibcode: 1975BAICz..26...38H
Altcode:
  A numerical method is presented for the simultaneous solution of
  the radiative transport equation and the equations of statistical
  equilibrium of level populations in the investigation of non-LTE
  line blanketing in the atmospheres of early-type stars. This method
  allows integrals over frequencies in radiation rates to be replaced
  by quadrature sums of a significantly lower order than previously
  used. Errors in radiation rates are estimated explicitly by introducing
  an error matrix. The obtained estimates of the matrix elements are
  used for calculating corrections to the radiation field during each
  iteration of the complete linearization procedure. The basic matrix size
  for this procedures significantly reduced, and more atomic transitions
  can be treated explicitly.

Title: Diagnostic methods in astrophysics.
Authors: Hekela, J.; Hubeny, I.
Bibcode: 1974CCpFS..24..477H
Altcode:
  Two basic ways of the spectroscopic diagnostics of the astrophysical
  plasma are briefly described. In the synthetic approach the problems
  are illustrated namely on the stellar atmospheres theory. In the
  analytical approach we deal especially with the methods of solution
  and the problems of mathematical stability.

Title: Optically thick lines in an expanding medium - synthetic
    approach formulation.
Authors: Hubený, I.
Bibcode: 1973saa..conf...65H
Altcode:
  No abstract at ADS

Title: Spatial spectroscopic diagnostic of planetary
    nebulae. III. Numerical investigation of local absolute monochromatic
    energies and local absolute energies in spherically symmetric models
Authors: Hekela, J.; Hubený, I.
Bibcode: 1972BAICz..23..331H
Altcode:
  No abstract at ADS

