Author name code: fabbian
ADS astronomy entries on 2022-09-14
author:"Fabbian, Damian"
------------------------------------------------------------------------  

Title: Do MURaM and STAGGER Simulations of Solar Faculae Match
    Observational Signatures from Magnetic Structures?
Authors: Cubas Armas, Melania; Fabbian, Damian
Bibcode: 2021ApJ...923..207C
Altcode:
  We compare results of simulations of solar facular-like conditions
  performed using the numerical codes MURaM and STAGGER. Both simulation
  sets have a similar setup, including the initial condition of ≍200
  G vertical magnetic flux. After interpolating the output physical
  quantities to constant optical depth, we compare them and test
  them against inversion results from solar observations. From the
  snapshots, we compute the monochromatic continuum in the visible
  and infrared, and the full Stokes vector of the Fe I spectral line
  pair around 6301-6302 Å. We compare the predicted spectral lines
  (at the simulation resolution and after smearing to the HINODE SP/SOT
  resolution) in terms of their main parameters for the Stokes I line
  profiles, and of their area and amplitude asymmetry for the Stokes V
  profiles. The codes produce magnetoconvection with similar appearance
  and distribution in temperature and velocity. The results also closely
  match the values from recent relevant solar observations. Although
  the overall distribution of the magnetic field is similar in both
  radiation-magnetohydrodynamic (RMHD) simulation sets, a detailed
  analysis reveals substantial disagreement in the field orientation,
  which we attribute to the differing boundary conditions. The resulting
  differences in the synthetic spectra disappear after spatial smearing
  to the resolution of the observations. We conclude that the two sets
  of simulations provide robust models of solar faculae. Nevertheless,
  we also find differences that call for caution when using results from
  RMHD simulations to interpret solar observational data.

Title: The CARMENES search for exoplanets around M dwarfs. Not-so-fine
    hyperfine-split vanadium lines in cool star spectra
Authors: Shan, Y.; Reiners, A.; Fabbian, D.; Marfil, E.; Montes,
   D.; Tabernero, H. M.; Ribas, I.; Caballero, J. A.; Quirrenbach, A.;
   Amado, P. J.; Aceituno, J.; Béjar, V. J. S.; Cortés-Contreras, M.;
   Dreizler, S.; Hatzes, A. P.; Henning, Th.; Jeffers, S. V.; Kaminski,
   A.; Kürster, M.; Lafarga, M.; Morales, J. C.; Nagel, E.; Pallé, E.;
   Passegger, V. M.; Rodriguez-López, C.; Schweitzer, A.; Zechmeister, M.
Bibcode: 2021A&A...654A.118S
Altcode: 2021arXiv210812442S
  Context. M-dwarf spectra are complex and notoriously difficult to model,
  posing challenges to understanding their photospheric properties and
  compositions in depth. Vanadium (V) is an iron-group element whose
  abundance supposedly closely tracks that of iron, but has origins that
  are not completely understood. <BR /> Aims: Our aim is to characterize
  a series of neutral vanadium atomic absorption lines in the 800-910
  nm wavelength region of high signal-to-noise, high-resolution,
  telluric-corrected M-dwarf spectra from the CARMENES survey. Many
  of these lines are prominent and exhibit a distinctive broad and
  flat-bottom shape, which is a result of hyperfine structure (HFS). We
  investigate the potential and implications of these HFS split lines
  for abundance analysis of cool stars. <BR /> Methods: With standard
  spectral synthesis routines, as provided by the spectroscopy software
  iSpec and the latest atomic data (including HFS) available from the
  VALD3 database, we modeled these striking line profiles. We used them
  to measure V abundances of cool dwarfs. <BR /> Results: We determined
  V abundances for 135 early M dwarfs (M0.0 V to M3.5 V) in the CARMENES
  guaranteed time observations sample. They exhibit a [V/Fe]-[Fe/H]
  trend consistent with that derived from nearby FG dwarfs. The tight
  (±0.1 dex) correlation between [V/H] and [Fe/H] suggests the potential
  application of V as an alternative metallicity indicator in M dwarfs. We
  also show hints that neglecting to model HFS could partially explain
  the temperature correlation in V abundance measurements observed in
  previous studies of samples involving dwarf stars with T<SUB>eff</SUB>
  ≲ 5300 K. <BR /> Conclusions: Our work suggests that HFS can impact
  certain absorption lines in cool photospheres more severely than in
  Sun-like ones. Therefore, we advocate that HFS should be carefully
  treated in abundance studies in stars cooler than ~5000 K. On the other
  hand, strong HFS split lines in high-resolution spectra present an
  opportunity for precision chemical analyses of large samples of cool
  stars. The V-to-Fe trends exhibited by the local M dwarfs continue
  to challenge theoretical models of V production in the Galaxy. <P
  />Full Table A.1 is only available at the CDS via anonymous ftp to
  <A href="http://cdsarc.u-strasbg.fr">cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/654/A118">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/654/A118</A>

Title: VizieR Online Data Catalog: Vanadium measurements for 135 M
    dwarfs (Shan+, 2021)
Authors: Shan, Y.; Reiners, A.; Fabbian, D.; Marfil, E.; Montes,
   D.; Tabernero, H. M.; Ribas, I.; Caballero, J. A.; Quirrenbach, A.;
   Amado, P. J.; Aceituno, J.; Bejar, V. J. S.; Cortes-Contreras, M.;
   Dreizler, S.; Hatzes, A. P.; Henning, T.; Jeffers, S. V.; Kaminski,
   A.; Kuerster, M.; Lafarga, M.; Morales, J. C.; Nagel, E.; Palle, E.;
   Passegger, V. M.; Rodriguez-Lopez, C.; Schweitzer, A.; Zechmeister, M.
Bibcode: 2021yCat..36540118S
Altcode:
  Table A1 presents the measured V abundances ([V/H]) for 135
  nearby early-M dwarfs from the CARMENES GTO sample. Two sets
  of measurements are given, which are based on two independently
  measured sets of fundamental stellar parameters for this sample
  (Schweitzer et al., 2019A&amp;A...625A..68S, Cat. J/A+A/625/A68 and
  Marfil et al., submitted). Rotational velocities from Reiners et
  al. (2018A&amp;A...612A..49R, Cat. J/A+A/612/A49) and disk kinematic
  membership designations (Cortes-Contreras+ in prep) are also
  included. <P />(1 data file).

Title: The Lines are Not Fine: Measuring Vanadium Abundances in M
    dwarfs from Hyperfine-Split Lines
Authors: Shan, Yutong; Reiners, Ansgar; Fabbian, Damian; Marfil,
   Emilio; Montes, David; Tabernero, Hugo M.; Ribas, Ignasi; Caballero,
   Jose A.; Quirrenbach, Andreas; Amado, Pedro J.; Aceituno, J.; Bejar,
   Victor J. S.; Cortes-Contreras, Miriam; Dreizler, Stefan; Hatzes,
   Artie P.; Henning, Thomas; Jeffers, Sandra V.; Kaminski, Adrian;
   Kürster, Martin; Lafarga, Marina; Morales, Juan Carlos; Nagel,
   Evangelos; Rodriguez-Lopez, Cristina; Passegger, Vera M.; Schweitzer,
   Andreas; Zechmeister, Mathias
Bibcode: 2021csss.confE.160S
Altcode:
  Cool star atmospheres present challenges to chemical abundance
  studies. To date, only a handful of elements have been quantified for
  a handful of M dwarfs. In high-resolution spectra from the CARMENES
  survey, we identify a series of dramatically hyperfine-split vanadium
  features between 800 and 910 nm, which have strong and clean profiles
  throughout the early M-dwarf range. These 'bucket-shaped' line regions
  can be well-modeled with standard model atmospheres combined with
  the latest atomic data from VALD. From these line regions, we measure
  vanadium abundances for 140 nearby early M dwarfs in the CARMENES GTO
  sample and confirm that they follow the same trend with metallicity
  as the FG-type stars in the solar neighborhood, i.e., significantly
  above predictions from galactic chemical evolution models. Exhibiting
  a tight correlation with iron, vanadium abundances show promise
  as a potential metallicity indicator for M dwarfs. We also present
  evidence that several well-known chemical studies of K dwarfs have
  systematically overestimated their vanadium abundances largely as a
  result of neglecting to model hyperfine structure, a bias that worsens
  with decreasing temperature. Our work highlights opportunities for
  robust chemical analysis of cool stars afforded by high-quality spectra
  redward of visible.

Title: Accurate Short-Characteristics Radiative Transfer in A
    Numerical Tool for Astrophysical RESearch (ANTARES)
Authors: Kostogryz, Nadiia M.; Kupka, Friedrich; Piskunov, Nikolai;
   Fabbian, Damian; Krüger, Daniel; Gizon, Laurent
Bibcode: 2021SoPh..296...46K
Altcode:
  We aim to improve the accuracy of radiative energy transport in
  three-dimensional radiation hydrodynamical simulations in ANTARES
  (A Numerical Tool for Astrophysical RESearch). We implement in the
  ANTARES short-characteristics numerical schemes a modification of
  the Bézier interpolant solver. This method yields a smoother surface
  structure in simulations of solar convection and reduces the artifacts
  appearing due to the limited number of rays along which the integration
  is done. Reducing such artifacts leads to increased stability of the
  code. We show that our new implementation achieves a better agreement
  of the temperature structure and its gradient with a semi-empirical
  model derived from observations, as well as of synthetic spectral-line
  profiles with the observed solar spectrum.

Title: The ANTARES code: recent developments and applications
Authors: Kupka, Friedrich; Zaussinger, Florian; Fabbian, Damian;
   Krüger, Daniel
Bibcode: 2020JPhCS1623a2016K
Altcode:
  ANTARES (A Numerical Tool for Astrophysical RESearch) is a
  multi-purpose numerical tool to solve different variants of the
  equations of hydrodynamics as they appear in problems of astrophysics,
  geophysics, and engineering sciences and which require the construction
  of detailed numerical simulation models. A presentation of the current
  feature set of the code with a focus on recent add-ons is given here
  in addition to a summary on several results from recent applications of
  ANTARES to solar physics, the physics of planets, and basic convection
  studies including the damping of pressure modes (solar oscillations)
  in numerical simulations of convection at the solar surface and the
  coupling of layers in numerical simulations of sheared and non-sheared
  double-diffusive convection.

Title: Comparing Radiative Transfer Codes and Opacity Samplings for
    Solar Irradiance Reconstructions
Authors: Criscuoli, Serena; Rempel, Matthias; Haberreiter, Margit;
   Pereira, Tiago M. D.; Uitenbroek, Han; Fabbian, Damian
Bibcode: 2020SoPh..295...50C
Altcode:
  Some techniques developed to reproduce solar irradiance variations make
  use of synthetic radiative fluxes of quiet and magnetic features. The
  synthesis of radiative fluxes of astronomical objects is likely
  to be affected by uncertainties resulting from approximations and
  specific input employed for the synthesis. In this work we compare
  spectra obtained with three radiative transfer codes with the
  purpose of investigating differences in reproducing solar irradiance
  variations. Specifically, we compare spectral synthesis produced in
  non-local thermodynamic equilibrium obtained with COSI and RH using
  1-D atmosphere models. We also compare local thermodynamic equilibrium
  syntheses emerging from 3-D MURaM simulations of the solar atmosphere
  obtained with two sets of opacity tables generated with the ATLAS9
  package and with the RH code, and test the effects of opacity sampling
  on the emergent spectra. We find that, although the different codes
  and methodologies employed to synthesize the spectrum reproduce overall
  the observed solar spectrum with a similar degree of accuracy, subtle
  differences in quiet Sun spectra may translate into larger differences
  in the computation of the contrasts of magnetic features, which,
  in turn, critically affect the estimates of solar variability.

Title: On long-duration 3D simulations of stellar convection using
    ANTARES
Authors: Kupka, F.; Fabbian, D.; Krüger, D.; Kostogryz, N.; Gizon, L.
Bibcode: 2020IAUGA..30..373K
Altcode:
  We present initial results from three-dimensional (3-D) radiation
  hydrodynamical simulations for the Sun and targeted Sun-like stars. We
  plan to extend these simulations up to several stellar days to study
  p-mode excitation and damping processes. The level of variation of
  irradiance on the time scales spanned by our 3-D simulations will
  be studied too. Here we show results from a first analysis of the
  computational data we produced so far.

Title: Shine BRITE: shedding light on stellar variability through
    advanced models
Authors: Fabbian, D.; Kupka, F.; Krüger, D.; Kostogryz, N. M.;
   Piskunov, N.
Bibcode: 2020svos.conf..155F
Altcode: 2020arXiv200201560F
  The correct interpretation of the large amount of complex data from
  next-generation (in particular, space-based) observational facilities
  requires a very strong theoretical underpinning. One can predict
  that, in the near future, the use of atmospheric models obtained with
  three-dimensional (3-D) radiation magneto-hydrodynamics (RMHD) codes,
  coupled with advanced radiative transfer treatment including non-local
  thermodynamic equilibrium (non-LTE) effects and polarisation, will
  become the norm. In particular, stellar brightness variability in cool
  stars (i.e., spectral types F-- M) can be caused by several different
  effects besides pulsation. In this review we have briefly discussed
  some published results, and mentioned aspects of recent progress. It
  then attempted to peek into what the future may hold for understanding
  this important aspect of the lives of stars.

Title: On the Challenges of synthetizing solar and stellar spectra
    for Irradiance reconstructions
Authors: Criscuoli, Serena; Rempel, Matthias D.; Haberreiter, Margit;
   Pereira, Tiago; Uitenbroek, Han; Fabbian, Damian
Bibcode: 2019AAS...23421702C
Altcode:
  Syntheses of solar and stellar spectra strongly depend on the adopted
  approximations and atomic and molecular databases. We compare LTE and
  NLTE syntheses of solar spectra obtained with widely used radiative
  transfer codes, utilizing both 3D-MHD simulations and 1D-static
  atmosphere models. We show that although different codes reproduce
  reasonably well the observed spectrum, subtle differences may translate
  into discrepancies of several tens of percents in the estimate of
  solar and stellar spectral irradiance variability.

Title: Comparison of Parameters from Three-Dimensional
    Magnetoconvection Simulations of the Solar Photosphere
Authors: Cubas Armas, M.; Fabbian, D.; Vitas, N.
Bibcode: 2019ASPC..526..195C
Altcode:
  We present preliminary results from a comparison of parameters
  derived from three-dimensional magnetohydrodynamic simulations of a
  plage obtained with the MURaM and STAGGER codes. We first compared the
  computed atmospheric physical parameters stored in the output temporal
  snapshots. Subsequently, we used the same snapshots as input to perform
  spectral synthesis calculations using the NICOLE code. We compared
  the synthetic Fe I 630.1 nm and 630.2 nm spectral lines in terms
  of central intensity, equivalent width, full width at half maximum,
  as well as area and amplitude asymmetry of the Stokes V profile.

Title: Magnetic Flux Density in 3D MHD Simulations and Observations
Authors: Beck, C.; Fabbian, D.; Rezaei, R.; Puschmann, K. G.
Bibcode: 2019ASPC..526..191B
Altcode:
  We compare the polarization signals induced in three-dimensional (3D)
  magneto-hydrodynamical (MHD) simulations by the Zeeman effect in the
  presence of photospheric magnetic fields to those in observations
  at disc centre. We consider quantities determined from Stokes vector
  profiles of observations of photospheric spectral lines in the visible
  and near-infrared, and in corresponding synthetic spectra obtained
  from numerical 3D MHD simulations with an average magnetic flux
  density of 20-200 G. We match the spatial resolution of observations
  by degrading the spectra of the simulations. We find that the total
  unsigned vertical magnetic flux density in the simulation should
  be less than 50 G to reproduce the observed polarization signals in
  the quiet Sun internetwork. A value of ∼30 G best agrees with all
  observations we employed.

Title: The variability of magnetic activity in solar-type stars
Authors: Fabbian, D.; Simoniello, R.; Collet, R.; Criscuoli, S.;
   Korhonen, H.; Krivova, N. A.; Oláh, K.; Jouve, L.; Solanki, S. K.;
   Alvarado-Gómez, J. D.; Booth, R.; García, R. A.; Lehtinen, J.;
   See, V.
Bibcode: 2017AN....338..753F
Altcode:
  No abstract at ADS

Title: The Polarization Signature of Photospheric Magnetic Fields
    in 3D MHD Simulations and Observations at Disk Center
Authors: Beck, C.; Fabbian, D.; Rezaei, R.; Puschmann, K. G.
Bibcode: 2017ApJ...842...37B
Altcode: 2017arXiv170506812B
  Before using three-dimensional (3D) magnetohydrodynamical (MHD)
  simulations of the solar photosphere in the determination of elemental
  abundances, one has to ensure that the correct amount of magnetic
  flux is present in the simulations. The presence of magnetic flux
  modifies the thermal structure of the solar photosphere, which affects
  abundance determinations and the solar spectral irradiance. The amount
  of magnetic flux in the solar photosphere also constrains any possible
  heating in the outer solar atmosphere through magnetic reconnection. We
  compare the polarization signals in disk-center observations of the
  solar photosphere in quiet-Sun regions with those in Stokes spectra
  computed on the basis of 3D MHD simulations having average magnetic
  flux densities of about 20, 56, 112, and 224 G. This approach allows
  us to find the simulation run that best matches the observations. The
  observations were taken with the Hinode SpectroPolarimeter (SP),
  the Tenerife Infrared Polarimeter (TIP), the Polarimetric Littrow
  Spectrograph (POLIS), and the GREGOR Fabry-Pèrot Interferometer
  (GFPI), respectively. We determine characteristic quantities of full
  Stokes profiles in a few photospheric spectral lines in the visible
  (630 nm) and near-infrared (1083 and 1565 nm). We find that the
  appearance of abnormal granulation in intensity maps of degraded
  simulations can be traced back to an initially regular granulation
  pattern with numerous bright points in the intergranular lanes
  before the spatial degradation. The linear polarization signals in
  the simulations are almost exclusively related to canopies of strong
  magnetic flux concentrations and not to transient events of magnetic
  flux emergence. We find that the average vertical magnetic flux density
  in the simulation should be less than 50 G to reproduce the observed
  polarization signals in the quiet-Sun internetwork. A value of about 35
  G gives the best match across the SP, TIP, POLIS, and GFPI observations.

Title: The missing 'M' ingredient in 3D photospheric simulations
    for solar abundances
Authors: Fabbian, Damian
Bibcode: 2017psio.confE..28F
Altcode:
  No abstract at ADS

Title: Lower solar atmosphere and magnetism at ultra-high spatial
    resolution
Authors: Collet, Remo; Criscuoli, Serena; Ermolli, Ilaria; Fabbian,
   Damian; Guerreiro, Nuno; Haberreiter, Margit; Peck, Courtney; Pereira,
   Tiago M. D.; Rempel, Matthias; Solanki, Sami K.; Wedemeyer-Boehm, Sven
Bibcode: 2016arXiv161202348C
Altcode:
  We present the scientific case for a future space-based telescope
  aimed at very high spatial and temporal resolution imaging of the
  solar photosphere and chromosphere. Previous missions (e.g., HINODE,
  SUNRISE) have demonstrated the power of observing the solar photosphere
  and chromosphere at high spatial resolution without contamination from
  Earth's atmosphere. We argue here that increased spatial resolution
  (from currently 70 km to 25 km in the future) and high temporal cadence
  of the observations will vastly improve our understanding of the
  physical processes controlling solar magnetism and its characteristic
  scales. This is particularly important as the Sun's magnetic field
  drives solar activity and can significantly influence the Sun-Earth
  system. At the same time a better knowledge of solar magnetism can
  greatly improve our understanding of other astrophysical objects.

Title: Spectroscopy at the Solar Limb: II. Are Spicules Heated to
    Coronal Temperatures?
Authors: Beck, C.; Rezaei, R.; Puschmann, K. G.; Fabbian, D.
Bibcode: 2016SoPh..291.2281B
Altcode: 2016arXiv160606132B; 2016SoPh..tmp..132B
  Spicules of the so-called type II were suggested to be relevant for
  coronal heating because of their ubiquity on the solar surface and
  their eventual extension into the corona. We investigate whether solar
  spicules are heated to transition-region or coronal temperatures and
  reach coronal heights (≫6 Mm) using multiwavelength observations
  of limb spicules in different chromospheric spectral lines (Ca II H,
  Hε , Hα , Ca II IR at 854.2 nm, He I at 1083 nm) taken with slit
  spectrographs and imaging spectrometers. We determine the line width
  of spectrally resolved line profiles in individual spicules and
  throughout the field of view, and estimate the maximal height that
  different types of off-limb features reach. We derive estimates of
  the kinetic temperature and the non-thermal velocity from the line
  width of spectral lines from different chemical elements. We find that
  most regular, i.e. thin and elongated, spicules reach a height of at
  most about 6 Mm above the solar limb. The majority of features found
  at larger heights are irregularly shaped with a significantly larger
  lateral extension, of up to a few Mm, than spicules. Both individual and
  average line profiles in all spectral lines show a decrease in their
  line width with height above the limb with very few exceptions. The
  kinetic temperature and the non-thermal velocity decrease with height
  above the limb. We find no indications that the spicules in our data
  reach coronal heights or transition-region or coronal temperatures.

Title: How different are the Liège and Hamburg atlases of the
    solar spectrum?
Authors: Doerr, H. -P.; Vitas, N.; Fabbian, D.
Bibcode: 2016A&A...590A.118D
Altcode: 2016arXiv160403748D
  Context. The high-fidelity solar spectral atlas prepared by
  <A HREF="http://adsabs.harvard.edu/abs/1973apds.book.....D">
  http://adsabs.harvard.edu/abs/1973apds.book.....D</A>
  Delbouille et al. (Liège atlas, 1973) and the atlas by
  <A HREF="http://adsabs.harvard.edu/abs/1999SoPh..184..421N">
  http://adsabs.harvard.edu/abs/1999SoPh..184..421N</A> Neckel (Hamburg
  atlas, 1999, Sol. Phys., 184, 421) are widely recognised as the most
  important collection of reference spectra of the Sun at disc centre in
  the visible wavelength range. The two datasets serve as fundamental
  resources for many researchers, in particular for chemical abundance
  analyses. But despite their similar published specifications (spectral
  resolution and noise level), the shapes of the spectral lines in the
  two atlases differ significantly and systematically. <BR /> Aims:
  Knowledge of any instrumental degradations is imperative to fully
  exploit the information content of spectroscopic data. We seek to
  investigate the magnitude of these differences and explain the possible
  sources. We provide the wavelength-dependent correction parameters that
  need to be taken into account when the spectra are to be compared with
  synthetic data, for instance. <BR /> Methods: A parametrically degraded
  version of the Hamburg spectrum was fitted to the Liège spectrum. The
  parameters of the model (wavelength shift, broadening, intensity
  scaling, and intensity offset) represent the different characteristics
  of the respective instruments, observational strategies, and data
  processing. <BR /> Results: The wavelength scales of the Liège and
  Hamburg atlases differ on average by 0.5 mÅ with a standard deviation
  of ± 2 mÅ, except for a peculiar region around 5500 Å. The continuum
  levels are offset by up to 18% below 5000 Å, but remain stably at a
  0.8% difference towards the red. We find no evidence for spectral stray
  light in the Liège spectrum. Its resolving power is almost independent
  of wavelength but limited to about 216 000, which is between two to
  six times lower than specified. When accounting for the degradations
  determined in this work, the spectra of the two atlases agree to within
  a few parts in 10<SUP>3</SUP>. <P />The fit parameters displayed in
  Fig. 2 and derived data are only available at the CDS via anonymous ftp
  to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
  (<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/590/A118">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/590/A118</A>

Title: VizieR Online Data Catalog: Differences of atlases of solar
    spectrum (Doerr+, 2016)
Authors: Doerr, H. -P.; Vitas, N.; Fabbian, D.
Bibcode: 2016yCat..35900118D
Altcode:
  A parametrically degraded version of the Hamburg spectrum was fitted
  to the Liege spectrum. The parameters of the model (wavelength shift,
  broadening, intensity scaling, intensity offset) represent the different
  characteristics of the respective instruments, observational strategies,
  and data processing. The fits were carried out for all identified solar
  lines in the line list provided by Pierce and Breckinridge (1973, The
  Kitt-Peak Table of Solar Spectrum Wavelengths, Vol. Contribution No. 559
  (Kitt Peak National Observatory); hereafter PB73) for an interval of
  Â±15pm around the line cores. From an initial testrun we found that
  the offset parameter (stray-light) is compatible with zero. The final
  fits were carried out with only three free parameters. The results
  from that run are provided in the file 'fitres.dat'. <P />A second
  file (liegepar.dat) contains derived parameters (spectral resolving
  power, position of the continuum) for the Liege spectrum that can be
  used in studies that compare Liege data to other data (e.g. synthetic
  spectra). <P />For instance, synthetic spectra have to be degraded to
  match the spectral resolving power of the Liege spectrum for a valid
  comparison. Our analysis showed that a Gaussian convolution kernel with
  a full-width at half-maximum (FWHM) of lambda/R (lambda: wavelength; R:
  spectral resolving power) is a very good approximation to the actual
  instrumental profile of the Liege atlas. <P />Likewise, the continuum
  of the Liege atlas at a particular wavelength can be matched to the
  continuum of the Hamburg atlas by division with the parameter 'C'
  from liegepar.dat. The correction parameters in liegepar.dat should
  be interpolated to the desired wavelength range before being applied
  in any data analysis. <P />We want to stress that the parameters
  provided here result from the fitting-procedure as described in the
  paper, with no further consistency checks or corrections applied. Some
  fits are affected by nearby telluric blends. We recommend to apply an
  outlier-rejection (e.g. a median filter) and/or smoothing before using
  the data. The results need to be carefully checked. <P />(2 data files).

Title: Constraining Solar/Stellar Activity and Magnetically-Driven
    Variability
Authors: Fabbian, Damian; Simoniello, Rosaria
Bibcode: 2016IBVS.6161....1F
Altcode:
  No abstract at ADS

Title: Continuum Intensity and [O I] Spectral Line Profiles in Solar
3D Photospheric Models: The Effect of Magnetic Fields
Authors: Fabbian, D.; Moreno-Insertis, F.
Bibcode: 2015ApJ...802...96F
Altcode: 2015arXiv150106916F
  The importance of magnetic fields in three-dimensional (3D)
  magnetoconvection models of the Sun’s photosphere is investigated
  in terms of their influence on the continuum intensity at different
  viewing inclination angles and on the intensity profile of two [O i]
  spectral lines. We use the RH numerical radiative transfer code to
  perform a posteriori spectral synthesis on the same time series of
  magnetoconvection models used in our publications on the effect of
  magnetic fields on abundance determination. We obtain a good match of
  the synthetic disk-center continuum intensity to the absolute continuum
  values from the Fourier Transform Spectrometer (FTS) observational
  spectrum; the match of the center-to-limb variation synthetic data
  to observations is also good, thanks, in part, to the 3D radiation
  transfer capabilities of the RH code. The different levels of magnetic
  flux in the numerical time series do not modify the quality of the
  match. Concerning the targeted [O i] spectral lines, we find, instead,
  that magnetic fields lead to nonnegligible changes in the synthetic
  spectrum, with larger average magnetic flux causing both of the lines
  to become noticeably weaker. The photospheric oxygen abundance that
  one would derive if instead using nonmagnetic numerical models would
  thus be lower by a few to several centidex. The inclusion of magnetic
  fields is confirmed to be important for improving the current modeling
  of the Sun, here in particular in terms of spectral line formation
  and of deriving consistent chemical abundances. These results may shed
  further light on the still controversial issue regarding the precise
  value of the solar oxygen abundance.

Title: The Tenth Data Release of the Sloan Digital Sky Survey:
    First Spectroscopic Data from the SDSS-III Apache Point Observatory
    Galactic Evolution Experiment
Authors: Ahn, Christopher P.; Alexandroff, Rachael; Allende Prieto,
   Carlos; Anders, Friedrich; Anderson, Scott F.; Anderton, Timothy;
   Andrews, Brett H.; Aubourg, Éric; Bailey, Stephen; Bastien, Fabienne
   A.; Bautista, Julian E.; Beers, Timothy C.; Beifiori, Alessandra;
   Bender, Chad F.; Berlind, Andreas A.; Beutler, Florian; Bhardwaj,
   Vaishali; Bird, Jonathan C.; Bizyaev, Dmitry; Blake, Cullen H.;
   Blanton, Michael R.; Blomqvist, Michael; Bochanski, John J.; Bolton,
   Adam S.; Borde, Arnaud; Bovy, Jo; Shelden Bradley, Alaina; Brandt,
   W. N.; Brauer, Dorothée; Brinkmann, J.; Brownstein, Joel R.; Busca,
   Nicolás G.; Carithers, William; Carlberg, Joleen K.; Carnero, Aurelio
   R.; Carr, Michael A.; Chiappini, Cristina; Chojnowski, S. Drew; Chuang,
   Chia-Hsun; Comparat, Johan; Crepp, Justin R.; Cristiani, Stefano;
   Croft, Rupert A. C.; Cuesta, Antonio J.; Cunha, Katia; da Costa, Luiz
   N.; Dawson, Kyle S.; De Lee, Nathan; Dean, Janice D. R.; Delubac,
   Timothée; Deshpande, Rohit; Dhital, Saurav; Ealet, Anne; Ebelke,
   Garrett L.; Edmondson, Edward M.; Eisenstein, Daniel J.; Epstein,
   Courtney R.; Escoffier, Stephanie; Esposito, Massimiliano; Evans,
   Michael L.; Fabbian, D.; Fan, Xiaohui; Favole, Ginevra; Femenía
   Castellá, Bruno; Fernández Alvar, Emma; Feuillet, Diane; Filiz
   Ak, Nurten; Finley, Hayley; Fleming, Scott W.; Font-Ribera, Andreu;
   Frinchaboy, Peter M.; Galbraith-Frew, J. G.; García-Hernández, D. A.;
   García Pérez, Ana E.; Ge, Jian; Génova-Santos, R.; Gillespie, Bruce
   A.; Girardi, Léo; González Hernández, Jonay I.; Gott, J. Richard,
   III; Gunn, James E.; Guo, Hong; Halverson, Samuel; Harding, Paul;
   Harris, David W.; Hasselquist, Sten; Hawley, Suzanne L.; Hayden,
   Michael; Hearty, Frederick R.; Herrero Davó, Artemio; Ho, Shirley;
   Hogg, David W.; Holtzman, Jon A.; Honscheid, Klaus; Huehnerhoff,
   Joseph; Ivans, Inese I.; Jackson, Kelly M.; Jiang, Peng; Johnson,
   Jennifer A.; Kinemuchi, K.; Kirkby, David; Klaene, Mark A.; Kneib,
   Jean-Paul; Koesterke, Lars; Lan, Ting-Wen; Lang, Dustin; Le Goff,
   Jean-Marc; Leauthaud, Alexie; Lee, Khee-Gan; Lee, Young Sun; Long,
   Daniel C.; Loomis, Craig P.; Lucatello, Sara; Lupton, Robert H.;
   Ma, Bo; Mack, Claude E., III; Mahadevan, Suvrath; Maia, Marcio
   A. G.; Majewski, Steven R.; Malanushenko, Elena; Malanushenko,
   Viktor; Manchado, A.; Manera, Marc; Maraston, Claudia; Margala,
   Daniel; Martell, Sarah L.; Masters, Karen L.; McBride, Cameron K.;
   McGreer, Ian D.; McMahon, Richard G.; Ménard, Brice; Mészáros,
   Sz.; Miralda-Escudé, Jordi; Miyatake, Hironao; Montero-Dorta,
   Antonio D.; Montesano, Francesco; More, Surhud; Morrison, Heather
   L.; Muna, Demitri; Munn, Jeffrey A.; Myers, Adam D.; Nguyen, Duy
   Cuong; Nichol, Robert C.; Nidever, David L.; Noterdaeme, Pasquier;
   Nuza, Sebastián E.; O'Connell, Julia E.; O'Connell, Robert W.;
   O'Connell, Ross; Olmstead, Matthew D.; Oravetz, Daniel J.; Owen,
   Russell; Padmanabhan, Nikhil; Palanque-Delabrouille, Nathalie; Pan,
   Kaike; Parejko, John K.; Parihar, Prachi; Pâris, Isabelle; Pepper,
   Joshua; Percival, Will J.; Pérez-Ràfols, Ignasi; Dotto Perottoni,
   Hélio; Petitjean, Patrick; Pieri, Matthew M.; Pinsonneault, M. H.;
   Prada, Francisco; Price-Whelan, Adrian M.; Raddick, M. Jordan; Rahman,
   Mubdi; Rebolo, Rafael; Reid, Beth A.; Richards, Jonathan C.; Riffel,
   Rogério; Robin, Annie C.; Rocha-Pinto, H. J.; Rockosi, Constance
   M.; Roe, Natalie A.; Ross, Ashley J.; Ross, Nicholas P.; Rossi,
   Graziano; Roy, Arpita; Rubiño-Martin, J. A.; Sabiu, Cristiano G.;
   Sánchez, Ariel G.; Santiago, Basílio; Sayres, Conor; Schiavon,
   Ricardo P.; Schlegel, David J.; Schlesinger, Katharine J.; Schmidt,
   Sarah J.; Schneider, Donald P.; Schultheis, Mathias; Sellgren, Kris;
   Seo, Hee-Jong; Shen, Yue; Shetrone, Matthew; Shu, Yiping; Simmons,
   Audrey E.; Skrutskie, M. F.; Slosar, Anže; Smith, Verne V.; Snedden,
   Stephanie A.; Sobeck, Jennifer S.; Sobreira, Flavia; Stassun, Keivan
   G.; Steinmetz, Matthias; Strauss, Michael A.; Streblyanska, Alina;
   Suzuki, Nao; Swanson, Molly E. C.; Terrien, Ryan C.; Thakar, Aniruddha
   R.; Thomas, Daniel; Thompson, Benjamin A.; Tinker, Jeremy L.; Tojeiro,
   Rita; Troup, Nicholas W.; Vandenberg, Jan; Vargas Magaña, Mariana;
   Viel, Matteo; Vogt, Nicole P.; Wake, David A.; Weaver, Benjamin A.;
   Weinberg, David H.; Weiner, Benjamin J.; White, Martin; White, Simon
   D. M.; Wilson, John C.; Wisniewski, John P.; Wood-Vasey, W. M.;
   Yèche, Christophe; York, Donald G.; Zamora, O.; Zasowski, Gail;
   Zehavi, Idit; Zhao, Gong-Bo; Zheng, Zheng; Zhu, Guangtun
Bibcode: 2014ApJS..211...17A
Altcode: 2013arXiv1307.7735A
  The Sloan Digital Sky Survey (SDSS) has been in operation since 2000
  April. This paper presents the Tenth Public Data Release (DR10) from
  its current incarnation, SDSS-III. This data release includes the first
  spectroscopic data from the Apache Point Observatory Galaxy Evolution
  Experiment (APOGEE), along with spectroscopic data from the Baryon
  Oscillation Spectroscopic Survey (BOSS) taken through 2012 July. The
  APOGEE instrument is a near-infrared R ~ 22,500 300 fiber spectrograph
  covering 1.514-1.696 μm. The APOGEE survey is studying the chemical
  abundances and radial velocities of roughly 100,000 red giant star
  candidates in the bulge, bar, disk, and halo of the Milky Way. DR10
  includes 178,397 spectra of 57,454 stars, each typically observed three
  or more times, from APOGEE. Derived quantities from these spectra
  (radial velocities, effective temperatures, surface gravities, and
  metallicities) are also included. DR10 also roughly doubles the number
  of BOSS spectra over those included in the Ninth Data Release. DR10
  includes a total of 1,507,954 BOSS spectra comprising 927,844 galaxy
  spectra, 182,009 quasar spectra, and 159,327 stellar spectra selected
  over 6373.2 deg<SUP>2</SUP>.

Title: APOGEE-2: The Second Phase of the Apache Point Observatory
    Galactic Evolution Experiment in SDSS-IV
Authors: Sobeck, Jennifer; Majewski, S.; Hearty, F.; Schiavon, R. P.;
   Holtzman, J. A.; Johnson, J.; Frinchaboy, P. M.; Skrutskie, M. F.;
   Munoz, R.; Pinsonneault, M. H.; Nidever, D. L.; Zasowski, G.; Garcia
   Perez, A.; Fabbian, D.; Meza Cofre, A.; Cunha, K. M.; Smith, V. V.;
   Chiappini, C.; Beers, T. C.; Steinmetz, M.; Anders, F.; Bizyaev, D.;
   Roman, A.; Fleming, S. W.; Crane, J. D.; SDSS-IV/APOGEE-2 Collaboration
Bibcode: 2014AAS...22344006S
Altcode:
  The second phase of the Apache Point Observatory Galactic Evolution
  Experiment (APOGEE-2), a part of the Sloan Digital Sky Survey IV
  (SDSS-IV), will commence operations in 2014. APOGEE-2 represents a
  significant expansion over APOGEE-1, not only in the size of the stellar
  sample, but also in the coverage of the sky through observations in both
  the Northern and Southern Hemispheres. Observations on the 2.5m Sloan
  Foundation Telescope of the Apache Point Observatory (APOGEE-2N) will
  continue immediately after the conclusion of APOGEE-1, to be followed
  by observations with the 2.5m du Pont Telescope of the Las Campanas
  Observatory (APOGEE-2S) within three years. Over the six-year lifetime
  of the project, high resolution (R∼22,500), high signal-to-noise
  (≥100) spectroscopic data in the H-band wavelength regime (1.51-1.69
  μm) will be obtained for several hundred thousand stars, more than
  tripling the total APOGEE-1 sample. Accurate radial velocities and
  detailed chemical compositions will be generated for target stars in
  the main Galactic components (bulge, disk, and halo), open/globular
  clusters, and satellite dwarf galaxies. The spectroscopic follow-up
  program of Kepler targets with the APOGEE-2N instrument will be
  continued and expanded. APOGEE-2 will significantly extend and enhance
  the APOGEE-1 legacy of scientific contributions to understanding the
  origin and evolution of the elements, the assembly and formation history
  of galaxies like the Milky Way, and fundamental stellar astrophysics.

Title: DR10 SDSS-III release of APOGEE data
Authors: Shetrone, Matthew D.; Allende-Prieto, C.; Beers, T. C.;
   Cunha, K. M.; Fabbian, D.; Feuillet, D.; Frinchaboy, P. M.; Garcia
   Perez, A.; Johnson, J.; Majewski, S. R.; Nidever, D. L.; Pinsonneault,
   M. H.; Smith, V. V.; Zasowski, G.; SDSS-III/APOGEE Collaboration
Bibcode: 2014AAS...22344002S
Altcode:
  SDSS-III's newest release is Data Release 10 (DR10). DR10 contains the
  first spectra of the APO Galactic Evolution Experiment (APOGEE). APOGEE
  is the first high-resolution (R ~ 22,500), high signal-to-noise ratio
  (S/N &gt;= 100 per resolution element), H-band (1.51 - 1.70 um) survey
  of all Galactic stellar populations (bulge, bar, disks, halo) with a
  uniform set of stellar tracers and spectral diagnostics. This poster
  will briefly describe the stellar sample included in DR10, review the
  data made available in DR10, consisting of fully calibrated, 1-d spectra
  radial velocities and the by-products of the APOGEE Stellar Parameters
  and Chemical Abundance Pipeline (ASPCAP): effective temperature, surface
  gravity, metallicity, and alpha, carbon and nitrogen abundances. We
  will also present the web tools that are available to the public and
  highlight the most critical warning and bad data flags.

Title: Ages of Solar Neighborhood Stars Using APOGEE
Authors: Feuillet, Diane; Holtzman, J. A.; Girardi, L.; Allende-Prieto,
   C.; Beers, T. C.; Cunha, K. M.; Fabbian, D.; Frinchaboy, P. M.;
   Hayden, M. R.; Majewski, S.
Bibcode: 2014AAS...22315209F
Altcode:
  The SDSS-III Apache Point Observatory Galactic Evolution Experiment
  (APOGEE) is a high resolution (R ~23,000) near-IR (H-band) spectroscopic
  survey of 100,000 Milky Way stars designed to chemically trace the
  formation and evolution of Galactic stellar populations. In addition
  to the primary survey, the APOGEE spectrograph has been fitted with
  10 fibers from the robotically controlled NMSU 1 m telescope to
  maximize the use of this instrument when not on sky with the Sloan
  2.5 m telescope. This allows for single object observations with this
  high resolution NIR spectrograph. Using this new capability provided
  by the 1 m, we are conducting a survey of bright stars (H &lt; 8)
  with accurate Hipparcos parallax measurements (μ_err &lt; 10%),
  which are not accessible to the main APOGEE survey. These data can be
  reduced and analyzed in the same way as main survey data, resulting
  in detailed chemical information for hundreds of nearby stars. The
  atmospheric parameters combined with the Hipparcos distances allow
  for age estimates of these stars. We present initial age estimates
  from isochrone matching to Padova isochrones, and an age-metallicity
  relation for the current sample.

Title: Thermodynamic fluctuations in solar photospheric
    three-dimensional convection simulations and observations
    (Corrigendum)
Authors: Beck, C.; Fabbian, D.; Moreno-Insertis, F.; Puschmann, K. G.;
   Rezaei, R.
Bibcode: 2013A&A...559C...1B
Altcode:
  No abstract at ADS

Title: Target Selection for the Apache Point Observatory Galactic
    Evolution Experiment (APOGEE)
Authors: Zasowski, G.; Johnson, Jennifer A.; Frinchaboy, P. M.;
   Majewski, S. R.; Nidever, D. L.; Rocha Pinto, H. J.; Girardi, L.;
   Andrews, B.; Chojnowski, S. D.; Cudworth, K. M.; Jackson, K.; Munn, J.;
   Skrutskie, M. F.; Beaton, R. L.; Blake, C. H.; Covey, K.; Deshpande,
   R.; Epstein, C.; Fabbian, D.; Fleming, S. W.; Garcia Hernandez, D. A.;
   Herrero, A.; Mahadevan, S.; Mészáros, Sz.; Schultheis, M.; Sellgren,
   K.; Terrien, R.; van Saders, J.; Allende Prieto, C.; Bizyaev, D.;
   Burton, A.; Cunha, K.; da Costa, L. N.; Hasselquist, S.; Hearty,
   F.; Holtzman, J.; García Pérez, A. E.; Maia, M. A. G.; O'Connell,
   R. W.; O'Donnell, C.; Pinsonneault, M.; Santiago, B. X.; Schiavon,
   R. P.; Shetrone, M.; Smith, V.; Wilson, J. C.
Bibcode: 2013AJ....146...81Z
Altcode: 2013arXiv1308.0351Z
  The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is
  a high-resolution infrared spectroscopic survey spanning all Galactic
  environments (i.e., bulge, disk, and halo), with the principal goal
  of constraining dynamical and chemical evolution models of the Milky
  Way. APOGEE takes advantage of the reduced effects of extinction
  at infrared wavelengths to observe the inner Galaxy and bulge at
  an unprecedented level of detail. The survey's broad spatial and
  wavelength coverage enables users of APOGEE data to address numerous
  Galactic structure and stellar populations issues. In this paper
  we describe the APOGEE targeting scheme and document its various
  target classes to provide the necessary background and reference
  information to analyze samples of APOGEE data with awareness of the
  imposed selection criteria and resulting sample properties. APOGEE's
  primary sample consists of ~10<SUP>5</SUP> red giant stars, selected
  to minimize observational biases in age and metallicity. We present the
  methodology and considerations that drive the selection of this sample
  and evaluate the accuracy, efficiency, and caveats of the selection and
  sampling algorithms. We also describe additional target classes that
  contribute to the APOGEE sample, including numerous ancillary science
  programs, and we outline the targeting data that will be included in
  the public data releases.

Title: Thermodynamic fluctuations in solar photospheric
    three-dimensional convection simulations and observations
Authors: Beck, C.; Fabbian, D.; Moreno-Insertis, F.; Puschmann, K. G.;
   Rezaei, R.
Bibcode: 2013A&A...557A.109B
Altcode: 2013arXiv1306.6093B
  Context. Numerical three-dimensional (3D) radiative
  (magneto-)hydrodynamical [(M)HD] simulations of solar convection
  are nowadays used to understand the physical properties of the solar
  photosphere and convective envelope, and, in particular, to determine
  the Sun's photospheric chemical abundances. To validate this approach,
  it is important to check that no excessive thermodynamic fluctuations
  arise as a consequence of the partially incomplete treatment of
  radiative transfer causing radiative damping that is too modest. <BR
  /> Aims: We investigate the realism of the thermodynamics in recent
  state-of-the-art 3D convection simulations of the solar atmosphere
  carried out with the Stagger code. <BR /> Methods: We compared the
  characteristic properties of several Fe i lines (557.6 nm, 630 nm, 1565
  nm) and one Si i line at 1082.7 nm in solar disc-centre observations
  of different spatial resolution with spectra synthesized from 3D
  convection simulations. The observations were taken with ground-based
  (Echelle spectrograph, Göttingen Fabry-Pérot Interferometer (GFPI),
  POlarimetric LIttrow Spectrograph, Tenerife Infrared Polarimeter, all
  at the Vacuum Tower Telescope on Tenerife) and space-based instruments
  (Hinode/Spectropolarimeter). We degraded the synthetic spectra to
  the spatial resolution of the observations, based on the distribution
  of the continuum intensity I<SUB>c</SUB>. We estimated the spectral
  degradation to be applied to the simulation results by comparing atlas
  spectra with averaged observed spectra. In addition to deriving a set
  of line parameters directly from the intensity profiles, we used the
  SIR (Stokes Inversion based on Response functions) code to invert
  the spectra. <BR /> Results: The spatial degradation kernels yield
  a similar generic spatial stray-light contamination of about 30%
  for all instruments. The spectral stray light inside the different
  spectrometers is found to be between 2% and 20%. Most of the line
  parameters from the observational data are matched by the degraded
  HD simulation spectra. The inversions predict a macroturbulent
  velocity v<SUB>mac</SUB> below 10 m s<SUP>-1</SUP> for the HD
  simulation spectra at full spatial resolution, whereas they yield
  v<SUB>mac</SUB> ≲ 1000 m s<SUP>-1</SUP> at a spatial resolution of
  0.″3. The temperature fluctuations in the inversion of the degraded
  HD simulation spectra do not exceed those from the observational data
  (of the order of 100-200 K rms for -2 ⪉ log τ<SUB>500 nm</SUB>
  ⪉ -0.5). The comparison of line parameters in spatially averaged
  profiles with the averaged values of line parameters in spatially
  resolved profiles indicates a significant change in (average) line
  properties on a spatial scale between 0.″13 and 0.″3. <BR />
  Conclusions: Up to a spatial resolution of 0.″3 (GFPI spectra),
  we find no indications of excessive thermodynamic fluctuations
  in the 3D HD simulation. To definitely confirm that simulations
  without spatial degradation contain fully realistic thermodynamic
  fluctuations requires observations at even higher spatial resolution
  (i.e. &lt;0.″13). <P />Appendices A and B are available in electronic
  form at <A href="http://www.aanda.org">http://www.aanda.org</A>

Title: Solar Fe abundance and magnetic fields. Towards a consistent
    reference metallicity
Authors: Fabbian, D.; Moreno-Insertis, F.; Khomenko, E.; Nordlund, Å.
Bibcode: 2012A&A...548A..35F
Altcode: 2012arXiv1209.2771F
  <BR /> Aims: We investigate the impact on Fe abundance determination of
  including magnetic flux in series of 3D radiation-magnetohydrodynamics
  (MHD) simulations of solar convection, which we used to synthesize
  spectral intensity profiles corresponding to disc centre. <BR />
  Methods: A differential approach is used to quantify the changes
  in theoretical equivalent width of a set of 28 iron spectral lines
  spanning a wide range in wavelength, excitation potential, oscillator
  strength, Landé factor, and formation height. The lines were computed
  in local thermodynamic equilibrium (LTE) using the spectral synthesis
  code LILIA. We used input magnetoconvection snapshots covering 50 min
  of solar evolution and belonging to series having an average vertical
  magnetic flux density of ⟨ B<SUB>vert</SUB> ⟩ = 0,50,100, and
  200 G. For the relevant calculations we used the Copenhagen Stagger
  code. <BR /> Results: The presence of magnetic fields causes both a
  direct (Zeeman-broadening) effect on spectral lines with non-zero
  Landé factor and an indirect effect on temperature-sensitive
  lines via a change in the photospheric T - τ stratification. The
  corresponding correction in the estimated atomic abundance ranges
  from a few hundredths of a dex up to |Δlog ɛ(Fe)<SUB>⊙</SUB>|
  ~ 0.15 dex, depending on the spectral line and on the amount of
  average magnetic flux within the range of values we considered. The
  Zeeman-broadening effect gains relatively more importance in the
  IR. The largest modification to previous solar abundance determinations
  based on visible spectral lines is instead due to the indirect effect,
  i.e., the line-weakening caused by a warmer stratification as seen on
  an optical depth scale. Our results indicate that the average solar
  iron abundance obtained when using magnetoconvection models can be ~
  0.03-0.11 dex higher than when using the simpler hydrodynamics (HD)
  convection approach. <BR /> Conclusions: We demonstrate that accounting
  for magnetic flux is important in state-of-the-art solar photospheric
  abundance determinations based on 3D convection simulations.

Title: Stray-light contamination and spatial deconvolution of
    slit-spectrograph observations
Authors: Beck, C.; Rezaei, R.; Fabbian, D.
Bibcode: 2011A&A...535A.129B
Altcode: 2011arXiv1109.2421B
  Context. Stray light caused by scattering on optical surfaces
  and in the Earth's atmosphere degrades the spatial resolution
  of observations. Whereas post-facto reconstruction techniques
  are common for 2D imaging and spectroscopy, similar options for
  slit-spectrograph data are rarely applied. <BR /> Aims: We study the
  contribution of stray light to the two channels of the POlarimetric
  LIttrow Spectrograph (POLIS) at 396 nm and 630 nm as an example of
  a slit-spectrograph instrument. We test the performance of different
  methods of stray-light correction and spatial deconvolution to improve
  the spatial resolution post-facto. <BR /> Methods: We model the stray
  light as having two components: a spectrally dispersed component and
  a "parasitic" component of spectrally undispersed light caused by
  scattering inside the spectrograph. We used several measurements to
  estimate the two contributions: a) observations with a (partly) blocked
  field of view (FOV); b) a convolution of the FTS spectral atlas; c)
  imaging of the spider mounting in the pupil plane; d) umbral profiles;
  and e) spurious polarization signal in telluric spectral lines. The
  measurements with a partly blocked FOV in the focal plane allowed us
  to estimate the spatial point spread function (PSF) of POLIS and the
  main spectrograph of the German Vacuum Tower Telescope (VTT). We then
  used the obtained PSF for a deconvolution of both spectroscopic and
  spectropolarimetric data and investigated the effect on the spectra. <BR
  /> Results: The parasitic contribution can be directly and accurately
  determined for POLIS, amounting to about 5% (0.3%) of the (continuum)
  intensity at 396 nm (630 nm). The spectrally dispersed stray light is
  less accessible because of its many contributing sources. We estimate
  a lower limit of about 10% across the full FOV for the dispersed stray
  light from umbral profiles. In quiet Sun regions, the stray-light level
  from the close surroundings (d &lt; 2'') of a given spatial point is
  about 20%. The stray light reduces to below 2% at a distance of 20''
  from a lit area for both POLIS and the main spectrograph. The spatial
  deconvolution using the PSF obtained improves the spatial resolution
  and increases the contrast, with a minor amplification of noise. <BR
  /> Conclusions: A two-component model of the stray-light contributions
  seems to be sufficient for a basic correction of observed spectra. The
  instrumental PSF obtained can be used to model the off-limb stray light,
  to determine the stray-light contamination accurately for observation
  targets with large spatial intensity gradients such as sunspots,
  and also to improve the spatial resolution of observations post-facto.

Title: (1) The effect of magnetic fields on solar abundance
    determinations (2) The solar photosphere in 3D. This time from
    observations
Authors: Fabbian, D.; Socas-Navarro, H.
Bibcode: 2010iac..talk..232F
Altcode: 2010iac..talk..186F
  No abstract at ADS

Title: Solar Abundance Corrections Derived Through Three-dimensional
    Magnetoconvection Simulations
Authors: Fabbian, D.; Khomenko, E.; Moreno-Insertis, F.; Nordlund, Å.
Bibcode: 2010ApJ...724.1536F
Altcode: 2010arXiv1006.0231F
  We explore the effect of the magnetic field when using realistic
  three-dimensional convection experiments to determine solar element
  abundances. By carrying out magnetoconvection simulations with a
  radiation-hydro code (the Copenhagen stagger code) and through a
  posteriori spectral synthesis of three Fe I lines, we obtain evidence
  that moderate amounts of mean magnetic flux cause a noticeable
  change in the derived equivalent widths compared with those for a
  non-magnetic case. The corresponding Fe abundance correction for a
  mean flux density of 200 G reaches up to ~0.1 dex in magnitude. These
  results are based on space- and time-averaged line profiles over a time
  span of 2.5 solar hours in the statistically stationary regime of the
  convection. The main factors causing the change in equivalent widths,
  namely the Zeeman broadening and the modification of the temperature
  stratification, act in different amounts and, for the iron lines
  considered here, in opposite directions; yet, the resulting |Δlog
  epsilon<SUB>sun</SUB>(Fe)| coincides within a factor of 2 in all
  of them, even though the sign of the total abundance correction
  is different for the visible and infrared lines. We conclude that
  magnetic effects should be taken into account when discussing precise
  values of the solar and stellar abundances and that an extended study
  is warranted.

Title: HD 172189: another step in furnishing one of the best
    laboratories known for asteroseismic studies
Authors: Creevey, O. L.; Uytterhoeven, K.; Martín-Ruiz, S.; Amado,
   P. J.; Niemczura, E.; van Winckel, H.; Suárez, J. C.; Rolland,
   A.; Rodler, F.; Rodríguez-López, C.; Rodríguez, E.; Raskin, G.;
   Rainer, M.; Poretti, E.; Pallé, P.; Molina, R.; Moya, A.; Mathias,
   P.; Le Guillou, L.; Hadrava, P.; Fabbian, D.; Garrido, R.; Decin,
   L.; Cutispoto, G.; Casanova, V.; Broeders, E.; Arellano Ferro, A.;
   Aceituno, F.
Bibcode: 2009A&A...507..901C
Altcode: 2009arXiv0909.3435C
  HD 172189 is a spectroscopic eclipsing binary system with a
  rapidly-rotating pulsating δ Scuti component. It is also a member of
  the open cluster IC 4756. These combined characteristics make it an
  excellent laboratory for asteroseismic studies. To date, HD 172189 has
  been analysed in detail photometrically but not spectroscopically. For
  this reason we have compiled a set of spectroscopic data to determine
  the absolute and atmospheric parameters of the components. We
  determined the radial velocities (RV) of both components using four
  different techniques. We disentangled the binary spectra using KOREL,
  and performed the first abundance analysis on both disentangled
  spectra. By combining the spectroscopic results and the photometric
  data, we obtained the component masses, 1.8 and 1.7 M<SUB>⊙</SUB>,
  and radii, 4.0 and 2.4 R<SUB>⊙</SUB>, for inclination i = 73.2°,
  eccentricity e = 0.28, and orbital period Π = 5.70198 days. Effective
  temperatures of 7600 K and 8100 K were also determined. The measured v
  sin i are 78 and 74 km s<SUP>-1</SUP>, respectively, giving rotational
  periods of 2.50 and 1.55 days for the components. The abundance analysis
  shows [Fe/H] = -0.28 for the primary (pulsating) star, consistent with
  observations of IC 4756. We also present an assessment of the different
  analysis techniques used to obtain the RVs and the global parameters.

Title: The C/O ratio at low metallicity: constraints on early chemical
    evolution from observations of Galactic halo stars
Authors: Fabbian, D.; Nissen, P. E.; Asplund, M.; Pettini, M.;
   Akerman, C.
Bibcode: 2009A&A...500.1143F
Altcode: 2008arXiv0810.0281F
  Aims: We present new measurements of the abundances of carbon and
  oxygen derived from high-excitation C i and O i absorption lines in
  metal-poor halo stars, with the aim of clarifying the main sources
  of these two elements in the early stages of the chemical enrichment
  of the Galaxy. <BR />Methods: We target 15 new stars compared to our
  previous study, with an emphasis on additional C/O determinations
  in the crucial metallicity range -3 ⪉ [Fe/H]⪉ -2. The stellar
  effective temperatures were estimated from the profile of the Hβ
  line. Departures from local thermodynamic equilibrium were accounted
  for in the line formation for both carbon and oxygen. The non-LTE
  effects are very strong at the lowest metallicities but, contrary
  to what has sometimes been assumed in the past due to a simplified
  assessment, of different degrees for the two elements. In addition,
  for the 28 stars with [Fe/H] &lt; -1 previously analysed, stellar
  parameters were re-derived and non-LTE corrections applied in the same
  fashion as for the rest of our sample, giving consistent abundances
  for 43 halo stars in total. <BR />Results: The new observations and
  non-LTE calculations strengthen previous suggestions of an upturn in
  C/O towards lower metallicity (particularly for [O/H] ⪉ -2). The
  C/O values derived for these very metal-poor stars are, however,
  sensitive to excitation via the still poorly quantified inelastic
  H collisions. While these do not significantly affect the non-LTE
  results for C i, they greatly modify the O i outcome. Adopting the
  H collisional cross-sections estimated from the classical Drawin
  formula leads to [C/O] ≈ 0 at [O/H] ≈ -3. To remove the upturn
  in C/O, near-LTE formation for O i lines would be required, which
  could only happen if the H collisional efficiency with the Drawin
  recipe is underestimated by factors of up to several tens of times,
  a possibility which we consider unlikely. <BR />Conclusions: The high
  C/O values derived at the lowest metallicities may be revealing the
  fingerprints of Population III stars or may signal rotationally-aided
  nucleosynthesis in more normal Population II stars. <P />Based on data
  collected with the European Southern Observatory's Very Large Telescope
  (VLT) at the Paranal, Chile (programmes No. 67.D-0106 and 73.D-0024)
  and with the Magellan Telescope at Las Campanas Observatory, Chile.

Title: Neutral oxygen spectral line formation revisited with new
collisional data: large departures from LTE at low metallicity
Authors: Fabbian, D.; Asplund, M.; Barklem, P. S.; Carlsson, M.;
   Kiselman, D.
Bibcode: 2009A&A...500.1221F
Altcode: 2009arXiv0902.4472F
  Aims: A detailed study is presented, including estimates of the
  impact on elemental abundance analysis, of the non-local thermodynamic
  equilibrium (non-LTE) formation of the high-excitation neutral oxygen
  777 nm triplet in model atmospheres representative of stars with
  spectral types F to K. <BR />Methods: We have applied the statistical
  equilibrium code MULTI to a number of plane-parallel MARCS atmospheric
  models covering late-type stars (4500 ≤ T_eff ≤ 6500 K, 2 ≤ log
  g ≤ 5 [cgs], and -3.5 ≤ [Fe/H] ≤ 0). The atomic model employed
  includes, in particular, recent quantum-mechanical electron collision
  data. <BR />Results: We confirm that the O i triplet lines form under
  non-LTE conditions in late-type stars, suffering negative abundance
  corrections with respect to LTE. At solar metallicity, the non-LTE
  effect, mainly attributed in previous studies to photon losses in the
  triplet itself, is also driven by an additional significant contribution
  from line opacity. At low metallicity, the very pronounced departures
  from LTE are due to overpopulation of the lower level (3s ^5S^o) of the
  transition. Large line opacity stems from triplet-quintet intersystem
  electron collisions, a form of coupling previously not considered or
  seriously underestimated. The non-LTE effects generally become severe
  for models (both giants and dwarfs) with higher T_eff. Interestingly,
  in metal-poor turn-off stars, the negative non-LTE abundance corrections
  tend to rapidly become more severe towards lower metallicity. When
  neglecting H collisions, they amount to as much as |Δlog ɛ_O|
  ~ 0.9 dex and ~1.2 dex, respectively at [Fe/H] = -3 and [Fe/H]
  = -3.5. Even when such collisions are included, the LTE abundance
  remains a serious overestimate, correspondingly by |Δlog ɛ_O| ~ 0.5
  dex and ~0.9 dex at such low metallicities. Although the poorly known
  inelastic hydrogen collisions thus remain an important uncertainty,
  the large metallicity-dependent non-LTE effects seem to point to
  a resulting “low” (compared to LTE) [O/Fe] in metal-poor halo
  stars. <BR />Conclusions: Our results may be important in solving
  the long-standing [O/Fe] debate. When applying the derived non-LTE
  corrections, the LTE oxygen abundance inferred from the 777 nm permitted
  triplet will be decreased substantially at low metallicity. If the
  classical Drawin formula is employed for O+H collisions, the derived
  [O/Fe] trend becomes almost flat below [Fe/H] ~ -1, in better agreement
  with recent literature estimates generally obtained from other oxygen
  abundance indicators. A value of [O/Fe] ⪉ +0.5 may therefore be
  appropriate, as suggested by standard theoretical models of type II
  supernovae nucleosynthetic yields. If neglecting impacts with H atoms
  instead, [O/Fe] decreases towards lower [Fe/H], which would open new
  questions. Our tests using ATLAS model atmospheres show that, though
  non-LTE corrections for metal-poor dwarfs are smaller (by ~0.2 dex
  when adopting efficient H collisions) than in the MARCS case, our
  main conclusions are preserved, and that the LTE approach tends to
  seriously overestimate the O abundance at low metallicity. However,
  in order to finally reach consistency between oxygen abundances from
  the different available spectral features, it is of high priority to
  reduce the large uncertainty regarding H collisions, to undertake a
  full investigation of the interplay of non-LTE and 3D effects, and to
  clarify the issue of the temperature scale at low metallicity.

Title: Chemical compositions of stars in the light of non-LTE spectral
line formation: The evolution of carbon and oxygen in the Galaxy
Authors: Fabbian, Damian
Bibcode: 2008PhDT.......131F
Altcode:
  No abstract at ADS

Title: [C/O] Observations in Low-[Fe/H] Halo Stars
Authors: Fabbian, D.; Nissen, P. E.; Asplund, M.; Akerman, C. J.;
   Pettini, M.
Bibcode: 2008psa..conf...45F
Altcode:
  We have observed 15 halo stars to determine the [C/O] behaviour at low
  [Fe/H]. Making use of our recent non-LTE calculations, which show
  that the high excitation C and O lines used in previous studies in
  the literature are affected by very significant departures from LTE,
  we aim to obtain accurate [C/O] ratios down to [Fe/H]∼ —3.2, which
  will enable us to shed light on the possible presence of an upturn of
  [C/O] at low metallicities.

Title: Sulphur Abundances in Metal-poor Stars
Authors: Nissen, P. E.; Akerman, C.; Asplund, M.; Fabbian, D.;
   Pettini, M.
Bibcode: 2008psa..conf...51N
Altcode:
  We report on sulphur abundances in halo stars as derived from near-IR
  UVES spectra. The importance of removing telluric lines and residual
  CCD fringing patterns by using early B-type stars as calibrators is
  emphasized. Comparison of data from the weak λ8694.6 and the stronger
  λ9212.9, 9237.5 pair of S I lines provides important constraints on
  non-LTE effects. We do not confirm the high sulphur abundances reported
  by others for some metal-poor stars; our results instead indicate that
  sulphur behaves like other typical α-capture elements with a plateau at
  [S/Fe] ∼ +0.3 dex in the Galactic halo.

Title: Chemical compositions of stars in the light of non-LTE spectral
line formation: the evolution of carbon and oxygen in the Galaxy
Authors: Fabbian, D.
Bibcode: 2008PhDT........12F
Altcode:
  Non-LTE effects affect the formation of many spectral features
  in the spectra of late-type stars. This thesis investigates the
  effect on carbon and oxygen abundances. The non-LTE calculations
  have been performed with the code MULTI, using MARCS atmospheric
  models with 4500&lt;Teff&lt;6500 K, 2&lt;log g&lt;5 [cgs], and
  -3.5&lt;[Fe/H]&lt;0. The large negative non-LTE abundance corrections
  found for high-excitation IR lines of both C I and O I previously used
  in the literature, are due to dilution of the line source function (due
  to photon losses in the lines) at solar metallicity, and to increased
  line opacity in non-LTE for metal-poor stars. The tendency of the
  non-LTE abundance corrections to become more important when moving to
  very low metallicity has important implications in terms of galactic
  chemical evolution. The results are applied to high-quality observation
  for a sample of 43 turnoff halo stars with -3.24&lt;[Fe/H]&lt;-1.10. At
  low-metallicity, in particular due to decreasing Si background opacity,
  the non-LTE corrections affecting the 777 nm oxygen triplet are found to
  be more significant than those affecting the C I lines. The presence of
  a [C/O] upturn at low [Fe/H], here for the first time based on a solid
  non-LTE analysis, is confirmed, pointing to significant C yields from
  early generations of stars. This could be tracing the products of so-far
  elusive earlier Population III stars, or may signal rotationally-aided
  nucleosynthesis in more normal Population II stars.

Title: Sulphur and zinc abundances in Galactic halo stars revisited
Authors: Nissen, P. E.; Akerman, C.; Asplund, M.; Fabbian, D.; Kerber,
   F.; Kaufl, H. U.; Pettini, M.
Bibcode: 2007A&A...469..319N
Altcode: 2007astro.ph..2689N
  Aims:Based on a new set of sulphur abundances in very metal-poor stars
  and an improved analysis of previous data, we aim at resolving current
  discrepancies on the trend of S/Fe vs. Fe/H and thereby gain better
  insight into the nucleosynthesis of sulphur. The trends of Zn/Fe and
  S/Zn will also be studied. <BR />Methods: High resolution VLT/UVES
  spectra of 40 main-sequence stars with -3.3 &lt; [Fe/H] &lt; -1.0 are
  used to derive S abundances from the weak λ 8694.6 S I line and the
  stronger λ λ 9212.9,9237.5 pair of S I lines. For one star, the S
  abundance is also derived from the S I triplet at 1.046 μm recently
  observed with the VLT infrared echelle spectrograph CRIRES. Fe and
  Zn abundances are derived from lines in the blue part of the UVES
  spectra, and effective temperatures are obtained from the profile
  of the Hβ line. <BR />Results: Comparison of sulphur abundances
  from the weak and strong S I lines provides important constraints on
  non-LTE effects. The high sulphur abundances reported by others for
  some metal-poor stars are not confirmed; instead, when taking non-LTE
  corrections into account, the Galactic halo stars distribute around a
  plateau at [S/Fe] ~ +0.2 dex with a scatter of 0.07 dex only. [Zn/Fe]
  is close to zero for metallicities in the range -2.0 &lt; [Fe/H]
  &lt; -1.0 but increases to a level of [Zn/Fe] ~ +0.1 to +0.2 dex in
  the range -2.7 &lt; [Fe/H] &lt; -2.0. At still lower metallicities
  [Zn/Fe] rises steeply to a value of [Zn/Fe] ~ +0.5 dex at [Fe/H] =
  -3.2. <BR />Conclusions: The trend of S/Fe vs. Fe/H corresponds to
  the trends of Mg/Fe, Si/Fe, and Ca/Fe and indicates that sulphur in
  Galactic halo stars has been made by α-capture processes in massive
  SNe. The observed scatter in S/Fe is much smaller than predicted from
  current stochastic models of the chemical evolution of the early Galaxy,
  suggesting that either the models or the calculated yields of massive
  SNe should be revised. We also examine the behaviour of S/Zn and find
  that departures from the solar ratio are significantly reduced at
  all metallicities if non-LTE corrections to the abundances of these
  two elements are adopted. This effect, if confirmed, would reduce the
  usefulness of the S/Zn ratio as a diagnostic of past star-formation
  activity, but would bring closer together the values measured in damped
  Lyman-alpha systems and in Galactic stars. <P />Based on observations
  collected at the European Southern Observatory at Paranal, Chile
  (programmes No. 67.D-0106, 73.D-0024 and CRIRES science verification
  program 60.A-9072). Table 1 and Appendices are only available in
  electronic form at http://www.aanda.org

Title: Sulphur Abundances in Metal-Poor Stars   First Result from
    CRIRES Science Verification
Authors: Nissen, Poul Erik; Asplund, Martin; Fabbian, Damian; Kerber,
   Florian; Käufl, Hans Ulrich; Pettini, Max
Bibcode: 2007Msngr.128...38N
Altcode:
  Sulphur is the tenth most abundant element in the Universe and plays an
  im-portant role in studies of the chemical enrichment and star formation
  history of distant galaxies. Due to the lack of suitable sulphur lines
  in the visible part of stellar spectra there is, however, still no
  agreement on the abundance of sulphur in Galactic metal poor stars,
  and we are therefore uncertain about the nucleosynthetic origin of
  sulphur. New observations of infrared sulphur lines with the cryogenic
  high resolution infrared echelle spectrograph (CRIRES) at ESO's VLT
  are helping to solve this problem.

Title: The non-LTE line formation of neutral carbon in late-type stars
Authors: Fabbian, D.; Asplund, M.; Carlsson, M.; Kiselman, D.
Bibcode: 2006A&A...458..899F
Altcode: 2006astro.ph..8284F
  Aims.We investigate the non-Local Thermodynamic Equilibrium (non-LTE)
  line formation of neutral carbon in late-type stars in order to remove
  some of the potential systematic errors in stellar abundance analyses
  employing C i features.<BR /> Methods: .The statistical equilibrium
  code MULTI was used on a grid of plane-parallel 1D MARCS atmospheric
  models.<BR /> Results: .Within the parameter space explored, the
  high-excitation C i lines studied are stronger in non-LTE due to
  the combined effect of line source function drop and increased line
  opacity due to overpopulation of the lower level for the transitions
  considered; the relative importance of the two effects depends on
  the particular combination of T<SUB>{eff</SUB>}, log g, [Fe/H] and
  [C/Fe] and on the analysed C i line. As a consequence, the non-LTE
  abundance corrections are negative and can be substantially so,
  for example ∼ -0.4 dex in halo turn-off stars at [Fe/H]∼ -3. The
  magnitude of the non-LTE corrections is rather insensitive to whether
  inelastic H collisions are included or not.<BR /> Conclusions: .Our
  results have implications on studies of nucleosynthetic processes and
  on Galactic chemical evolution models. When applying our calculated
  corrections to recent observational data, the upturn in [C/O] at low
  metallicity might still be present (thus apparently still necessitating
  contributions from massive Pop. III stars for the carbon production),
  but at a lower level and possibly with a rather shallow trend of ∼
  -0.2 dex/dex below [O/H]∼ -1.

Title: Ci Non-LTE Spectral Line Formation in Late-Type Stars
Authors: Fabbian, D.; Asplund, M.; Carlsson, M.
Bibcode: 2006cams.book...52F
Altcode:
  We present the results from our non-LTE investigation for neutral
  carbon, which was carried out to remove potential systematic errors
  in stellar abundance analyses. The calculations were performed for
  late-type stars and give substantial negative non-LTE abundance
  corrections. When applied to observations of extremely metal-poor
  stars, which within the LTE framework seem to suggest a possible [C/O]
  uprise at low metallicities (Akerman et al. 2004), these improvements
  will have important implications, enabling us to understand if the
  standard chemical evolution model is adequate, with no need to invoke
  signatures by Pop. III stars for the carbon nucleosynthesis.

Title: Abundance Anomalies in Hot Horizontal Branch Stars of the
    Galactic Globular Cluster NGC 1904
Authors: Recio-Blanco, A.; Fabbian, D.; Gratton, R. G.
Bibcode: 2006cams.book..151R
Altcode:
  We present abundance measurements, based on high resolution optical
  spectroscopic data obtained with the UVES at VLT, for 10 stars in
  the blue horizontal branch (BHB) of the Galactic globular cluster NGC
  1904 (M79). In agreement with previous findings for other clusters,
  we obtain normal abundances for stars cooler than Te. ~ 11000 K, and
  largely anomalous abundances for hotter stars: large He depletions
  and overabundances of Fe, Ti, Cr, P and Mn. The abundances of Mg, Si
  and Ca are roughly normal, in the hot stars as well as in the cooler
  ones. This abundance pattern can be attributed to the onset of diffusion
  and to radiation pressure in the stable atmospheres of hot HB stars. A
  possibly related discontinuity in the stellar rotation rate seems also
  to occur at Te. ~ 11000 K.

Title: Abundance anomalies in hot horizontal branch stars of the
    galactic globular cluster NGC1904
Authors: Fabbian, D.; Recio-Blanco, A.; Gratton, R. G.; Piotto, G.
Bibcode: 2005A&A...434..235F
Altcode: 2005astro.ph..1321F
  We present abundance measurements, based on high-resolution optical
  spectroscopic data obtained with the Ultraviolet and Visual Echelle
  Spectrograph mounted on Kueyen (Very Large Telescope UT2), for ten
  stars in the extended blue horizontal branch of the Galactic globular
  cluster NGC 1904 (M79). In agreement with previous findings for other
  clusters, we obtain normal abundances for stars cooler than T_eff∼
  11 000 K, and largely anomalous abundances for hotter stars: large He
  depletions, and overabundances of Fe, Ti, Cr, P and Mn. The abundances
  of Mg, Si and Ca are roughly normal, in the hot stars as well as in the
  cooler ones. This abundance pattern can be attributed to the onset of
  diffusion and to radiation pressure in the stable atmospheres of hot
  horizontal branch stars.

Title: Effective temperatures and lithium abundances of halo
    turnoff stars
Authors: Nissen, P. E.; Akerman, C.; Asplund, M.; Fabbian, D.;
   Pettini, M.
Bibcode: 2005IAUS..228..101N
Altcode:
  Effective temperatures of 30 turnoff stars with -3.2 {[Fe/H]{
  have been derived from the profiles of Balmer lines in high S/N,
  VLT/UVES spectra. While the systematic error of T<SUB>eff</SUB> may
  be of the order of 100K, the differential values of T<SUB>eff</SUB>
  are determined with a one-sigma precision of ∼25K. These precise
  T<SUB>eff</SUB> values are used in a study of the slope and dispersion
  of the Li abundance as a function of [Fe/H]. A small, but significant
  cosmic dispersion in A(Li) appears to be present exemplified by the
  two very metal-poor stars G64-12 and G64-37.

Title: CI non LTE spectral line formation in late-type stars
Authors: Fabbian, D.; Asplund, M.; Carlsson, M.; Kiselman, D.
Bibcode: 2005IAUS..228..255F
Altcode: 2005astro.ph..8063F
  We present non-Local Thermodynamic Equilibrium (non-LTE) calculations
  for neutral carbon spectral line formation, carried out for a grid
  of model atmospheres covering the range of late-type stars. The
  results of our detailed calculations suggest that the carbon
  non-LTE corrections in these stars are higher than usually adopted,
  remaining substantial even at low metallicity. For the most metal-poor
  stars in the sample of Akerman et al (2004), the effects are of the
  order of Δlogɛ<SUB>C</SUB> ≃ -0.35ldots-0.45 (when neglecting H
  collisions). Applying our results to those observations, the apparent
  [C/O] upturn seen in their LTE analysis is no longer present, thus
  revealing no need to invoke contributions from Pop. III stars to the
  carbon nucleosynthesis.

Title: VizieR Online Data Catalog: Abundances of BHB stars in NGC 1904
    (Fabbian+, 2005)
Authors: Fabbian, D.; Recio-Blanco, A.; Gratton, R. G.; Piotto, G.
Bibcode: 2005yCat..34340235F
Altcode:
  The abundance measurements are based on high-resolution optical
  spectroscopical data, obtained during 2 observing runs with the
  Ultraviolet and Visual Echelle Spectrograph mounted on Kueyen
  (Very Large Telescope UT2). Ten target stars in the extended blue
  horizontal branch of the Galactic globular cluster NGC 1904 (M79)
  have been analysed. <P />(2 data files).

Title: Chemical and Rotational Properties of Cluster Hot HB Stars.
Authors: Recio-Blanco, Alejandra; Piotto, Giampaolo; Gratton, Raffaele;
   Fabbian, Damian; Aparicio, Antonio
Bibcode: 2003IAUJD...4E..11R
Altcode:
  In this contribution we analize the chemical and rotational properties
  of a sample of hot HB stars in the globular clusters M15 M79 M80 and
  NGC 2808 with effective temperatures T<SUB>eff</SUB> between 7000 K
  and 25000 K. To this purpose we have used high resolution spectroscopy
  with UVES+VLT. Our study reveals the existence of a discontinuity in
  the rotational rate distribution with temperature detected also by
  Behr et al. 1999 and 2000 in M13 and M15. Stars with Teff&lt; 11000
  K show a range of vsini values up to 30 km/s. All the stars with Teff
  &gt; 11000 K however are slow rotators with vsini &lt; 12 km/s. This
  discontinuity seems to coincide with the onset of diffusive processes
  in the stellar atmosphere which cause abundance anomalies in the hotter
  stars: overabundances of metals and helium depletion. This is confirmed
  also by the chemical analysis performed in 10 of the M79 targets in
  which we have found evidences of radiative levitation of metals and
  gravitational settling of helium for stars with temperatures hotter
  than 11000 K.

