Author name code: demarque
ADS astronomy entries on 2022-09-14
author:"Demarque, Pierre" 
------------------------------------------------------------------------  

Title: Discovery of strong progenitor age dependence of type Ia
    supernova luminosity standardization process and discordance in
    cosmology
Authors: Lee, Young-Wook; Chung, Chul; Demarque, Pierre; Park,
   Seunghyun; Son, Junhyuk; Kang, Yijung
Bibcode: 2021arXiv210706288L
Altcode:
  Supernova (SN) cosmology is based on the assumption that the
  width-luminosity relation (WLR) and the color-luminosity relation
  (CLR) in the type Ia SN luminosity standardization would not vary with
  progenitor age. Unlike this expectation, recent age datings of stellar
  populations in host galaxies have shown significant correlations between
  progenitor age and Hubble residual (HR). It was not clear, however, how
  this correlation arises from the SN luminosity standardization process,
  and how this would impact the cosmological result. Here we show that
  this correlation originates from a strong progenitor age dependence of
  the WLR and the CLR, in the sense that SNe from younger progenitors
  are fainter each at given light-curve parameters $x_1$ and $c$. This
  is reminiscent of Baade's discovery of two Cepheid period-luminosity
  relations, and, as such, causes a serious systematic bias with redshift
  in SN cosmology. Other host properties show substantially smaller and
  insignificant differences in the WLR and CLR for the same dataset. We
  illustrate that the differences between the high-$z$ and low-$z$ SNe
  in the WLR and CLR, and in HR after the standardization, are fully
  comparable to those between the correspondingly young and old SNe at
  intermediate redshift, indicating that the observed dimming of SNe
  with redshift is most likely an artifact of over-correction in the
  luminosity standardization. When this systematic bias with redshift
  is properly taken into account, there is no or little evidence left
  for an accelerating universe, posing a serious question to one of the
  cornerstones of the concordance model.

Title: Stellar evolution models with entropy-calibrated mixing-length
parameter: application to red giants
Authors: Spada, Federico; Demarque, Pierre; Kupka, Friedrich
Bibcode: 2021MNRAS.504.3128S
Altcode: 2021arXiv210408067S; 2021MNRAS.tmp.1089S
  We present evolutionary models for solar-like stars with an improved
  treatment of convection that results in a more accurate estimate of
  the radius and effective temperature. This is achieved by improving
  the calibration of the mixing-length parameter, which sets the length
  scale in the 1D convection model implemented in the stellar evolution
  code. Our calibration relies on the results of 2D and 3D radiation
  hydrodynamics simulations of convection to specify the value of the
  adiabatic specific entropy at the bottom of the convective envelope in
  stars as a function of their effective temperature, surface gravity, and
  metallicity. For the first time, this calibration is fully integrated
  within the flow of a stellar evolution code, with the mixing-length
  parameter being continuously updated at run-time. This approach replaces
  the more common, but questionable, procedure of calibrating the length
  scale parameter on the Sun, and then applying the solar-calibrated
  value in modelling other stars, regardless of their mass, composition,
  and evolutionary status. The internal consistency of our current
  implementation makes it suitable for application to evolved stars, in
  particular to red giants. We show that the entropy calibrated models
  yield a revised position of the red giant branch that is in better
  agreement with observational constraints than that of standard models.

Title: Testing the entropy calibration of the radii of cool stars:
    models of α Centauri A and B
Authors: Spada, Federico; Demarque, Pierre
Bibcode: 2019MNRAS.489.4712S
Altcode: 2019MNRAS.tmp.2125S; 2019arXiv190900701S
  We present models of α Centauri A and B implementing an entropy
  calibration of the mixing-length parameter α<SUB>MLT</SUB>, recently
  developed and successfully applied to the Sun (Spada et al. 2018, ApJ,
  869, 135). In this technique the value of α<SUB>MLT</SUB> in the 1D
  stellar evolution code is calibrated to match the adiabatic specific
  entropy derived from 3D radiation-hydrodynamics simulations of stellar
  convective envelopes, whose effective temperature, surface gravity, and
  metallicity are selected consistently along the evolutionary track. The
  customary treatment of convection in stellar evolution models relies
  on a constant, solar-calibrated α<SUB>MLT</SUB>. There is, however,
  mounting evidence that this procedure does not reproduce the observed
  radii of cool stars satisfactorily. For instance, modelling α Cen
  A and B requires an ad hoc tuning of α<SUB>MLT</SUB> to distinct,
  non-solar values. The entropy-calibrated models of α Cen A and B
  reproduce their observed radii within 1{{ per cent}} (or better) without
  externally adjusted parameters. The fit is of comparable quality to that
  of models with freely adjusted α<SUB>MLT</SUB> for α Cen B (within
  1σ), while it is less satisfactory for α Cen A (within 2.5σ). This
  level of accuracy is consistent with the intrinsic uncertainties of
  the method. Our results demonstrate the capability of the entropy
  calibration method to produce stellar models with radii accurate
  within 1{{ per cent}}. This is especially relevant in characterizing
  exoplanet-host stars and their planetary systems accurately.

Title: Improved Calibration of the Radii of Cool Stars Based on 3D
Simulations of Convection: Implications for the Solar Model
Authors: Spada, F.; Demarque, P.; Basu, S.; Tanner, J. D.
Bibcode: 2018ApJ...869..135S
Altcode: 2018arXiv181101817S
  Main-sequence, solar-like stars (M ≲ 1.5 M <SUB>⊙</SUB>)
  have outer convective envelopes that are sufficiently thick to
  affect significantly their overall structure. The radii of these
  stars, in particular, are sensitive to the details of inefficient,
  superadiabatic convection occurring in their outermost layers. The
  standard treatment of convection in stellar evolution models, based
  on the mixing-length theory (MLT), provides only a very approximate
  description of convection in the superadiabatic regime. Moreover, it
  contains a free parameter, α <SUB>MLT</SUB>, whose standard calibration
  is based on the Sun and is routinely applied to other stars, ignoring
  the differences in their global parameters (e.g., effective temperature,
  gravity, chemical composition) and previous evolutionary history. In
  this paper, we present a calibration of α <SUB>MLT</SUB> based on 3D
  radiation hydrodynamics (RHD) simulations of convection. The value of α
  <SUB>MLT</SUB> is adjusted to match the specific entropy in the deep,
  adiabatic layers of the convective envelope to the corresponding value
  obtained from the 3D RHD simulations, as a function of the position
  of the star in the ({log}g,{log}{T}<SUB>eff</SUB>}) plane and its
  chemical composition. We have constructed a model of the present-day
  Sun using such entropy-based calibration. We find that its past
  luminosity evolution is not affected by the entropy calibration. The
  predicted solar radius, however, exceeds that of the standard model
  during the past several billion years, resulting in a lower surface
  temperature. This illustrative calculation also demonstrates the
  viability of the entropy approach for calibrating the radii of other
  late-type stars.

Title: YaPSI: a new database of evolutionary tracks and isochrones
Authors: Spada, F.; Demarque, P.; Kim, Y. -C.; Boyajian, T. S.;
   Brewer, J. M.
Bibcode: 2018IAUS..334..362S
Altcode:
  The Yale-Potsdam Stellar Isochrones (YaPSI) cover the low and
  intermediate stellar mass regime (0.15 to 5.0 M<SUB>⊙</SUB>) for a
  wide range of solar-scaled chemical compositions (metallicity from
  -0.5 to +0.3; helium mass fraction from 0.25 to 0.37, assigned
  independently of each other). The tracks are finely spaced in
  mass, to allow for accurate interpolation. The models feature
  state-of-the-art input physics relevant to low-mass stars modeling
  (surface boundary conditions, equation of state), thus updating the
  faint end of the Yonsei-Yale (YY) isochrones. Utility codes, such
  as an isochrone interpolator in age, metallicity and helium content,
  are also provided. The YaPSI isochrones are in good agreement with the
  empirical mass-luminosity and mass-radius relations available to date,
  and provide satisfactory fitting of the color-magnitude diagrams of
  well-studied open clusters.

Title: Final Hubble Space Telescope Astrometry of the Procyon
    Binary System
Authors: Bond, Howard E.; Gilliland, Ronald L.; Schaefer, Gail
   H.; Barstow, Martin A.; Demarque, Pierre; Holberg, Jay B.;
   Kozhurina-Platais, Vera
Bibcode: 2018RNAAS...2..147B
Altcode: 2018RNAAS...2c.147B
  Not Available <P />Based on observations with the NASA/ESA Hubble Space
  Telescope obtained at Space Telescope Science Institute, operated by
  Association of Universities for Research in Astronomy, Inc., under
  NASA contract NAS5-26555.

Title: The Sirius System and Its Astrophysical Puzzles: Hubble Space
    Telescope and Ground-based Astrometry
Authors: Bond, Howard E.; Schaefer, Gail H.; Gilliland, Ronald L.;
   Holberg, Jay B.; Mason, Brian D.; Lindenblad, Irving W.; Seitz-McLeese,
   Miranda; Arnett, W. David; Demarque, Pierre; Spada, Federico; Young,
   Patrick A.; Barstow, Martin A.; Burleigh, Matthew R.; Gudehus, Donald
Bibcode: 2017ApJ...840...70B
Altcode: 2017arXiv170310625B
  Sirius, the seventh-nearest stellar system, is a visual binary
  containing the metallic-line A1 V star Sirius A, the brightest star
  in the sky, orbited in a 50.13 year period by Sirius B, the brightest
  and nearest white dwarf (WD). Using images obtained over nearly two
  decades with the Hubble Space Telescope (HST), along with photographic
  observations covering almost 20 years and nearly 2300 historical
  measurements dating back to the 19th century, we determine precise
  orbital elements for the visual binary. Combined with the parallax and
  the motion of the A component, these elements yield dynamical masses
  of 2.063+/- 0.023 {M}<SUB>⊙ </SUB> and 1.018+/- 0.011 {M}<SUB>⊙
  </SUB> for Sirius A and B, respectively. Our precise HST astrometry
  rules out third bodies orbiting either star in the system, down
  to masses of ∼15-25 {M}<SUB>{Jup</SUB>}. The location of Sirius
  B in the Hertzsprung-Russell diagram is in excellent agreement with
  theoretical cooling tracks for WDs of its dynamical mass, and implies a
  cooling age of ∼126 Myr. The position of Sirius B on the mass-radius
  plane is also consistent with WD theory, assuming a carbon-oxygen
  core. Including the pre-WD evolutionary timescale of the assumed
  progenitor, the total age of Sirius B is about 228 ± 10 Myr. We
  calculated evolutionary tracks for stars with the dynamical mass of
  Sirius A, using two independent codes. We find it necessary to assume
  a slightly subsolar metallicity, of about 0.85 {Z}<SUB>⊙ </SUB>, to
  fit its location on the luminosity-radius plane. The age of Sirius A
  based on these models is about 237-247 Myr, with uncertainties of ±15
  Myr, consistent with that of the WD companion. We discuss astrophysical
  puzzles presented by the Sirius system, including the probability that
  the two stars must have interacted in the past, even though there
  is no direct evidence for this and the orbital eccentricity remains
  high. <P />Based in part on observations with the NASA/ESA Hubble
  Space Telescope obtained at the Space Telescope Science Institute,
  and from the Mikulski Archive for Space Telescopes at STScI, which are
  operated by the Association of Universities for Research in Astronomy,
  Inc., under NASA contract NAS5-26555.

Title: VizieR Online Data Catalog: Historical and HST Astrometry of
    Sirius A,B (Bond+, 2017)
Authors: Bond, H. E.; Schaefer, G. H.; Gilliland, R. L.; Holberg,
   J. B.; Mason, B. D.; Lindenblad, I. W.; Seitz-McLeese, M.; Arnett,
   W. D.; Demarque, P.; Spada, F.; Young, P. A.; Barstow, M. A.; Burleigh,
   M. R.; Gudehus, D.
Bibcode: 2017yCat..18400070B
Altcode:
  We have assembled a compilation of published historical measurements of
  the position angle (PA) and the angular separation of Sirius B relative
  to Sirius A. Our tabulation is based on a critical review of measures
  contained in the Washington Double Star Catalog maintained at the USNO
  and from our additional literature searches. Notes included in the
  tabulation give extensive commentary on the historical observations. <P
  />Many early publications provided measures averaged over multiple
  nights or even an entire observing season for the purpose of reducing
  computational labor in subsequent analyses. With modern computers, there
  is no need for such averaging, so we opted to present the individual
  measures whenever available. However, if an observer reported more than
  one measurement on a given night, we did compute the mean position
  for that night. If the original publication only reported a mean
  across several nights, we tabulated that mean as reported. <P />The
  visual micrometer observations did not always include a contemporaneous
  measurement of both the PA and separation. These omissions are listed as
  -99.0 in the table. The measurement uncertainties were assigned through
  our orbital fitting method described in the paper. Measurements that
  were rejected from the orbital solution are identified in the Notes
  column and are listed with uncertainties of 0. <P />(3 data files).

Title: The Yale-Potsdam Stellar Isochrones
Authors: Spada, F.; Demarque, P.; Kim, Y. -C.; Boyajian, T. S.;
   Brewer, J. M.
Bibcode: 2017ApJ...838..161S
Altcode: 2017arXiv170303975S
  We introduce the Yale-Potsdam Stellar Isochrones (YaPSI), a new
  grid of stellar evolution tracks and isochrones of solar-scaled
  composition. In an effort to improve the Yonsei-Yale database, special
  emphasis is placed on the construction of accurate low-mass models
  ({M}<SUB>* </SUB>&lt; 0.6 {M}<SUB>⊙ </SUB>), and in particular on
  their mass-luminosity and mass-radius relations, both crucial for
  characterizing exoplanet-host stars, and, in turn, their planetary
  systems. The YaPSI models cover the mass range 0.15-5.0 {M}<SUB>⊙
  </SUB> densely enough to permit detailed interpolation in mass, and
  the metallicity and helium abundance ranges [Fe/H] = -1.5 to +0.3
  and Y <SUB>0</SUB> = 0.25-0.37 are specified independently of each
  other (i.e., no fixed {{Δ }}Y/{{Δ }}Z relation is assumed). The
  evolutionary tracks are calculated from the pre-main sequence up to
  the tip of the red giant branch. The isochrones, with ages between 1
  Myr and 20 Gyr, provide UBVRI colors in the Johnson-Cousins system,
  and JHK colors in the homogenized Bessell &amp; Brett system,
  derived from two different semi-empirical {T}<SUB>eff</SUB>}-color
  calibrations from the literature. We also provide utility codes,
  such as an isochrone interpolator, in age, metallicity, and helium
  content, and an interface of the tracks with an open-source Monte
  Carlo Markov-Chain tool for the analysis of individual stars. Finally,
  we present comparisons of the YaPSI models with the best empirical
  mass-luminosity and mass-radius relations available to date, as well
  as isochrone fitting of well-studied stellar clusters.

Title: HST Observations of Astrophysically Important Visual Binaries
Authors: Bond, Howard E.; Barstow, Martin; Burleigh, Matthew; Demarque,
   Pierre; Gilliland, Ronald L.; Girard, Terrence M.; Gudehus, Donald H.;
   Holberg, Jay B.; Nelan, Edmund; Schaefer, Gail
Bibcode: 2016hst..prop14342B
Altcode:
  We propose to continue our long-term program of astrometry of close
  visual binaries, with the primary goal of determining purely dynamical
  masses for 3 important main-sequence stars and 9 white dwarfs (WDs). A
  secondary aim is to set limits on third bodies in the systems down to
  planetary mass. Three of our targets are naked-eye stars with much
  fainter companions that are extremely difficult to image from the
  ground. Our other 2 targets are double WDs, whose small separations and
  faintness likewise make them difficult to measure using ground-based
  techniques. Observations have been completed for a 3rd double WD. <P
  />The bright stars, to be imaged with WFC3, are: (1) Procyon (P = 40.83
  yr), containing a bright F star and a much fainter WD companion. With
  the continued monitoring proposed here, we will obtain masses to an
  accuracy of better than 1%, providing a testbed for theories of both
  Sun-like stars and WDs. (2) Sirius (P = 50.14 yr), an A-type star also
  having a faint WD companion, Sirius B, the nearest and brightest of all
  WDs. (3) Mu Cas (P = 21.08 yr), a nearby metal-deficient G dwarf for
  which accurate masses will lead to the stars' helium contents, with
  cosmological implications. <P />The faint double WDs, to be observed
  with FGS, are: (1) G 107-70 (P = 18.84 yr), and (2) WD 1818+126 (P =
  12.19 yr). Our astrometry of these systems will add 4 accurate masses
  to the handful of WD masses that are directly known from dynamical
  measurements. The FGS measurements will also provide precise parallaxes
  for the systems, a necessary ingredient in the mass determinations.

Title: Entropy in Adiabatic Regions of Convection Simulations
Authors: Tanner, Joel D.; Basu, Sarbani; Demarque, Pierre
Bibcode: 2016ApJ...822L..17T
Altcode: 2016arXiv160407437T
  One of the largest sources of uncertainty in stellar models is caused
  by the treatment of convection in stellar envelopes. One-dimensional
  stellar models often make use of the mixing length or equivalent
  approximations to describe convection, all of which depend on various
  free parameters. There have been attempts to rectify this by using
  3D radiative-hydrodynamic simulations of stellar convection, and in
  trying to extract an equivalent mixing length from the simulations. In
  this Letter, we show that the entropy of the deeper, adiabatic layers
  in these simulations can be expressed as a simple function of {log}g
  and {log}{T}<SUB>{{eff</SUB>}}, which holds potential for calibrating
  stellar models in a simple and more general manner.

Title: Hubble Space Telescope Astrometry of the Procyon System
Authors: Bond, Howard E.; Gilliland, Ronald L.; Schaefer, Gail H.;
   Demarque, Pierre; Girard, Terrence M.; Holberg, Jay B.; Gudehus,
   Donald; Mason, Brian D.; Kozhurina-Platais, Vera; Burleigh, Matthew
   R.; Barstow, Martin A.; Nelan, Edmund P.
Bibcode: 2015ApJ...813..106B
Altcode: 2015arXiv151000485B
  The nearby star Procyon is a visual binary containing the F5 IV-V
  subgiant Procyon A, orbited in a 40.84-year period by the faint DQZ
  white dwarf (WD) Procyon B. Using images obtained over two decades with
  the Hubble Space Telescope, and historical measurements back to the
  19th century, we have determined precise orbital elements. Combined
  with measurements of the parallax and the motion of the A component,
  these elements yield dynamical masses of 1.478 ± 0.012 M<SUB>⊙</SUB>
  and 0.592 ± 0.006 M<SUB>⊙</SUB> for A and B, respectively. The
  mass of Procyon A agrees well with theoretical predictions based on
  asteroseismology and its temperature and luminosity. Use of a standard
  core-overshoot model agrees best for a surprisingly high amount of core
  overshoot. Under these modeling assumptions, Procyon A’s age is ∼2.7
  Gyr. Procyon B’s location in the H-R diagram is in excellent agreement
  with theoretical cooling tracks for WDs of its dynamical mass. Its
  position in the mass-radius plane is also consistent with theory,
  assuming a carbon-oxygen core and a helium-dominated atmosphere. Its
  progenitor’s mass was 1.9-2.2 M<SUB>⊙</SUB>, depending on its
  amount of core overshoot. Several astrophysical puzzles remain. In the
  progenitor system, the stars at periastron were separated by only ∼5
  AU, which might have led to tidal interactions and even mass transfer;
  yet there is no direct evidence that these have occurred. Moreover the
  orbital eccentricity has remained high (∼0.40). The mass of Procyon
  B is somewhat lower than anticipated from the initial-to-final-mass
  relation seen in open clusters. The presence of heavy elements in
  its atmosphere requires ongoing accretion, but the place of origin is
  uncertain. <P />Based on observations with the NASA/ESA Hubble Space
  Telescope obtained at the Space Telescope Science Institute, and from
  the Mikulski Archive for Space Telescopes at STScI, which are operated
  by the Association of Universities for Research in Astronomy, Inc.,
  under NASA contract NAS5-26555.

Title: Observations of Binary Stars with the Differential Speckle
    Survey Instrument. V. Toward an Empirical Metal-Poor Mass-Luminosity
    Relation
Authors: Horch, Elliott P.; van Altena, William F.; Demarque, Pierre;
   Howell, Steve B.; Everett, Mark E.; Ciardi, David R.; Teske, Johanna
   K.; Henry, Todd J.; Winters, Jennifer G.
Bibcode: 2015AJ....149..151H
Altcode: 2015arXiv150300363H
  In an effort to better understand the details of the stellar structure
  and evolution of metal-poor stars, the Gemini North telescope was used
  on two occasions to take speckle imaging data of a sample of known
  spectroscopic binary stars and other nearby stars in order to search for
  and resolve close companions. The observations were obtained using the
  Differential Speckle Survey Instrument, which takes data in two filters
  simultaneously. The results presented here are of 90 observations of
  23 systems in which one or more companions was detected, and six stars
  where no companion was detected to the limit of the camera capabilities
  at Gemini. In the case of the binary and multiple stars, these results
  are then further analyzed to make first orbit determinations in five
  cases, and orbit refinements in four other cases. The mass information
  is derived, and since the systems span a range in metallicity, a study
  is presented that compares our results with the expected trend in total
  mass as derived from the most recent Yale isochrones as a function
  of metal abundance. These data suggest that metal-poor main-sequence
  stars are less massive at a given color than their solar-metallicity
  analogues in a manner consistent with that predicted from the theory.

Title: Stellar diameters and temperatures - VI. High angular
    resolution measurements of the transiting exoplanet host stars HD
    189733 and HD 209458 and implications for models of cool dwarfs
Authors: Boyajian, Tabetha; von Braun, Kaspar; Feiden, Gregory A.;
   Huber, Daniel; Basu, Sarbani; Demarque, Pierre; Fischer, Debra A.;
   Schaefer, Gail; Mann, Andrew W.; White, Timothy R.; Maestro, Vicente;
   Brewer, John; Lamell, C. Brooke; Spada, Federico; López-Morales,
   Mercedes; Ireland, Michael; Farrington, Chris; van Belle, Gerard T.;
   Kane, Stephen R.; Jones, Jeremy; ten Brummelaar, Theo A.; Ciardi,
   David R.; McAlister, Harold A.; Ridgway, Stephen; Goldfinger, P. J.;
   Turner, Nils H.; Sturmann, Laszlo
Bibcode: 2015MNRAS.447..846B
Altcode: 2015MNRAS.447..850B; 2014arXiv1411.5638B
  We present direct radii measurements of the well-known transiting
  exoplanet host stars HD 189733 and HD 209458 using the CHARA Array
  interferometer. We find the limb-darkened angular diameters to be
  θ<SUB>LD</SUB> = 0.3848 ± 0.0055 and 0.2254 ± 0.0072 mas for
  HD 189733 and HD 209458, respectively. HD 189733 and HD 209458 are
  currently the only two transiting exoplanet systems where detection of
  the respective planetary companion's orbital motion from high-resolution
  spectroscopy has revealed absolute masses for both star and planet. We
  use our new measurements together with the orbital information
  from radial velocity and photometric time series data, Hipparcos
  distances, and newly measured bolometric fluxes to determine the stellar
  effective temperatures (T<SUB>eff</SUB> = 4875 ± 43, 6092 ± 103 K),
  stellar linear radii (R<SUB>*</SUB> = 0.805 ± 0.016, 1.203 ± 0.061
  R<SUB>⊙</SUB>), mean stellar densities (ρ<SUB>*</SUB> = 1.62 ± 0.11,
  0.58 ± 0.14 ρ<SUB>⊙</SUB>), planetary radii (R<SUB>p</SUB> = 1.216
  ± 0.024, 1.451 ± 0.074 R<SUB>Jup</SUB>), and mean planetary densities
  (ρ<SUB>p</SUB> = 0.605 ± 0.029, 0.196 ± 0.033 ρ<SUB>Jup</SUB>) for
  HD 189733b and HD 209458b, respectively. The stellar parameters for HD
  209458, an F9 dwarf, are consistent with indirect estimates derived from
  spectroscopic and evolutionary modelling. However, we find that models
  are unable to reproduce the observational results for the K2 dwarf,
  HD 189733. We show that, for stellar evolutionary models to match the
  observed stellar properties of HD 189733, adjustments lowering the
  solar-calibrated mixing-length parameter to α<SUB>MLT</SUB> =1.34
  need to be employed.

Title: Empirically determined properties of the K-dwarf HD 189733
    and implications for evolutionary models of low-mass stars
Authors: Boyajian, Tabetha S.; von Braun, Kaspar; Feiden, Gregory
   A.; Huber, Daniel; Basu, Sarbani; Demarque, Pierre; Fischer, Debra;
   Schaefer, Gail; White, Timothy; Maestro, Vicente; Brewer, John Michael;
   Lamell, Brooke; Spada, Federico; Mann, Andrew; Lopez-Morales, Mercedes;
   Ireland, Michael; Farrington, Christopher D.; van Belle, Gerard; Kane,
   Stephen R.; Jones, Jeremy; Ten Brummelaar, Theo; Ciardi, David R.;
   McAlister, Harold A.; Ridgway, Stephen T.; goldfinger, PJ
Bibcode: 2015AAS...22525703B
Altcode:
  We present direct measurements of the stellar radii and effective
  temperatures for HD189733 and HD209458 (see poster by von Braun
  et al.). We use the stellar radius and temperature along with the
  mass from the Keplerian orbital solution to explore deviations with
  model predictions. The stellar properties for HD209458, a F9 dwarf,
  are consistent with indirect estimates derived from spectroscopic
  and evolutionary modeling. However, we find that models are unable to
  reproduce the observational results for the K2 dwarf, HD 189733. We show
  that, for stellar evolutionary models to match the observed stellar
  properties of HD 189733, adjustments lowering the solar-calibrated
  mixing length parameter need to be employed.

Title: Fundamental Parameters of the Two Hall-of-Famers HD 189733
    and HD 209458
Authors: von Braun, Kaspar; Boyajian, Tabetha S.; Feiden, Gregory
   A.; Huber, Daniel; Basu, Sarbani; Demarque, Pierre; Fischer, Debra;
   Schaefer, Gail; White, Timothy; Maestro, Vicente; Brewer, John Michael;
   Lamell, Brooke; Spada, Federico; Mann, Andrew; Lopez-Morales, Mercedes;
   Ireland, Michael; Farrington, Christopher D.; van Belle, Gerard; Kane,
   Stephen R.; Jones, Jeremy; Ten Brummelaar, Theo; Ciardi, David R.;
   McAlister, Harold A.; Ridgway, Stephen T.; Goldfinger, PJ
Bibcode: 2015AAS...22525702V
Altcode:
  HD 189733 and HD 209458 are two of the most thoroughly studied exoplanet
  systems. They also represent the only transiting systems for which
  spectroscopy studies have produced radial velocity signatures of both
  the planets and the parent stars, yielding direct mass measurements. We
  present the results of our interferometric radius measurements and
  spectrophotometric observations of these two hall-of-fame exoplanet
  hosts. Our results, combined with trigonometric parallaxes and
  literature broad-band photometry, yield empirical values for
  stellar and planetary radii and stellar effective temperatures
  and luminosities. Using the directly determined component masses
  from previous studies, we calculate surface gravities and bulk
  densities for the parent stars and their exoplanets, creating a nearly
  model-independent set of fundamental astrophysical parameters for two
  of exoplanet science's most important stepping stones.

Title: Modeling Convective Core Overshoot and Diffusion in Procyon
    Constrained by Asteroseismic Data
Authors: Guenther, D. B.; Demarque, P.; Gruberbauer, M.
Bibcode: 2014ApJ...787..164G
Altcode: 2014arXiv1404.6153G
  We compare evolved stellar models, which match Procyon's mass and
  position in the HR diagram, to current ground-based asteroseismic
  observations. Diffusion of helium and metals along with two conventional
  core overshoot descriptions and the Kuhfuss nonlocal theory of
  convection are considered. We establish that one of the two published
  asteroseismic data reductions for Procyon, which mainly differ in their
  identification of even versus odd l values, is a significantly more
  probable and self-consistent match to our models than the other. The
  most probable models according to our Bayesian analysis have evolved to
  just short of turnoff, still retaining a hydrogen convective core. Our
  most probable models include Y and Z diffusion and have conventional
  core overshoot between 0.9 and 1.5 pressure scale heights, which
  increases the outer radius of the convective core by between 36% and
  43%, respectively. We discuss the significance of this comparatively
  higher than expected core overshoot amount in terms of internal mixing
  during evolution. The parameters of our most probable models are similar
  regardless of whether adiabatic or nonadiabatic model p-mode frequencies
  are compared to the observations, although, the Bayesian probabilities
  are greater when the nonadiabatic model frequencies are used. All the
  most probable models (with or without core overshoot, adiabatic or
  nonadiabatic model frequencies, diffusion or no diffusion, including
  priors for the observed HRD location and mass or not) have masses that
  are within 1σ of the observed mass 1.497 ± 0.037 M <SUB>⊙</SUB>.

Title: The Effect of Metallicity-dependent T-τ Relations on
    Calibrated Stellar Models
Authors: Tanner, Joel D.; Basu, Sarbani; Demarque, Pierre
Bibcode: 2014ApJ...785L..13T
Altcode: 2014arXiv1402.1182T
  Mixing length theory is the predominant treatment of convection in
  stellar models today. Usually described by a single free parameter, α,
  the common practice is to calibrate it using the properties of the Sun,
  and apply it to all other stellar models as well. Asteroseismic data
  from Kepler and CoRoT provide precise properties of other stars which
  can be used to determine α as well, and a recent study of stars in the
  Kepler field of view found α to vary with metallicity. Interpreting
  α obtained from calibrated stellar models, however, is complicated
  by the fact that the value for α depends on the surface boundary
  condition of the stellar model, or T-τ relation. Calibrated models
  that use typical T-τ relations, which are static and insensitive to
  chemical composition, do not include the complete effect of metallicity
  on α. We use three-dimensional radiation-hydrodynamic simulations to
  extract metallicity-dependent T-τ relations and use them in calibrated
  stellar models. We find the previously reported α-metallicity trend
  to be robust, and not significantly affected by the surface boundary
  condition of the stellar models.

Title: The Chemical Composition Dependence of Stellar Envelope
    Convection and Overshoot
Authors: Tanner, J. D.; Basu, S.; Demarque, P.
Bibcode: 2013ASPC..478..377T
Altcode:
  Using a grid of 3D hydrodynamic simulations in the outer layers of
  convection, we examine how properties of convection and overshoot
  are affected by the heavy element and helium abundance. We find that
  simulations with high-Z or low-Y exhibit larger mean and turbulent
  velocities throughout the superadiabatic region; they also have more
  overshoot than the low-Z or high-Y ones. Using the turbulent velocity
  field from simulations, we also find that helium-induced changes to
  the atmospheric dynamics results in different absolute Doppler shifts
  of weak spectral lines.

Title: Helium-abundance and Other Composition Effects on the
    Properties of Stellar Surface Convection in Solar-like Main-sequence
    Stars
Authors: Tanner, Joel D.; Basu, Sarbani; Demarque, Pierre
Bibcode: 2013ApJ...778..117T
Altcode: 2013arXiv1310.0475T
  We investigate the effect of helium abundance and α-element enhancement
  on the properties of convection in envelopes of solar-like main-sequence
  stars using a grid of three-dimensional radiation hydrodynamic
  simulations. Helium abundance increases the mean molecular weight of
  the gas and alters opacity by displacing hydrogen. Since the scale of
  the effect of helium may depend on the metallicity, the grid consists
  of simulations with three helium abundances (Y = 0.1, 0.2, 0.3),
  each with two metallicities (Z = 0.001, 0.020). We find that changing
  the helium mass fraction generally affects structure and convective
  dynamics in a way opposite to that of metallicity. Furthermore,
  the effect is considerably smaller than that of metallicity. The
  signature of helium differs from that of metallicity in the manner in
  which the photospheric velocity distribution is affected. We also find
  that helium abundance and surface gravity behave largely in similar
  ways, but differ in the way they affect the mean molecular weight. A
  simple model for spectral line formation suggests that the bisectors
  and absolute Doppler shifts of spectral lines depend on the helium
  abundance. We look at the effect of α-element enhancement and find
  that it has a considerably smaller effect on the convective dynamics
  in the superadiabatic layer compared to that of helium abundance.

Title: The Radius Discrepancy in Low-mass Stars: Single versus
    Binaries
Authors: Spada, F.; Demarque, P.; Kim, Y. -C.; Sills, A.
Bibcode: 2013ApJ...776...87S
Altcode: 2013arXiv1308.5558S
  A long-standing issue in the theory of low-mass stars is the discrepancy
  between predicted and observed radii and effective temperatures. In
  spite of the increasing availability of very precise radius
  determinations from eclipsing binaries and interferometric measurements
  of radii of single stars, there is no unanimous consensus on the extent
  (or even the existence) of the discrepancy and on its connection with
  other stellar properties (e.g., metallicity, magnetic activity). We
  investigate the radius discrepancy phenomenon using the best data
  currently available (accuracy &lt;~ 5%). We have constructed a grid of
  stellar models covering the entire range of low-mass stars (0.1-1.25
  M <SUB>⊙</SUB>) and various choices of the metallicity and mixing
  length parameter, α. We used an improved version of the Yale Rotational
  stellar Evolution Code, implementing surface boundary conditions based
  on the most up-to-date PHOENIX atmosphere models. Our models are in
  good agreement with others in the literature and improve and extend
  the low mass end of the Yale-Yonsei isochrones. Our calculations
  include rotation-related quantities, such as moments of inertia and
  convective turnover timescales, useful in studies of magnetic activity
  and rotational evolution of solar-like stars. Consistent with previous
  works, we find that both binaries and single stars have radii inflated
  by about 3% with respect to the theoretical models; among binaries,
  the components of short orbital period systems are found to be the
  most deviant. We conclude that both binaries and single stars are
  comparably affected by the radius discrepancy phenomenon.

Title: Variation of Stellar Envelope Convection and Overshoot with
    Metallicity
Authors: Tanner, Joel D.; Basu, Sarbani; Demarque, Pierre
Bibcode: 2013ApJ...767...78T
Altcode: 2013arXiv1302.5707T
  We examine how metallicity affects convection and overshoot in the
  superadiabatic layer of main sequence stars. We present results from
  a grid of three-dimensional radiation hydrodynamic simulations with
  four metallicities (Z = 0.040, 0.020, 0.010, 0.001), and spanning
  a range in effective temperature (4950 &lt; T <SUB>eff</SUB> &lt;
  6230). We show that changing the metallicity alters properties of
  the convective gas dynamics, and the structure of the superadiabatic
  layer and atmosphere. Our grid of simulations shows that the amount
  of superadiabaticity, which tracks the transition from efficient to
  inefficient convection, is sensitive to changes in metallicity. We find
  that increasing the metallicity forces the location of the transition
  region to lower densities and pressures, and results in larger mean
  and turbulent velocities throughout the superadiabatic region. We
  also quantify the degree of convective overshoot in the atmosphere,
  and show that it increases with metallicity as well.

Title: Comparing the Effect of Radiative Transfer Schemes on
    Convection Simulations
Authors: Tanner, Joel D.; Basu, Sarbani; Demarque, Pierre
Bibcode: 2012ApJ...759..120T
Altcode: 2012arXiv1209.3784T
  We examine the effect of different radiative transfer schemes on
  the properties of three-dimensional (3D) simulations of near-surface
  stellar convection in the superadiabatic layer, where energy transport
  transitions from fully convective to fully radiative. We employ two
  radiative transfer schemes that fundamentally differ in the way they
  cover the 3D domain. The first solver approximates domain coverage
  with moments, while the second solver samples the 3D domain with
  ray integrations. By comparing simulations that differ only in their
  respective radiative transfer methods, we are able to isolate the effect
  that radiative efficiency has on the structure of the superadiabatic
  layer. We find the simulations to be in good general agreement,
  but they show distinct differences in the thermal structure in the
  superadiabatic layer and atmosphere.

Title: Modelling fully convective stars in eclipsing binaries:
    KOI-126 and CM Draconis
Authors: Spada, F.; Demarque, P.
Bibcode: 2012MNRAS.422.2255S
Altcode: 2012arXiv1202.4468S
  We present models of the components of the systems KOI-126 and CM
  Draconis, the two eclipsing binary systems known to date to contain
  stars with masses low enough to have fully convective interiors. We are
  able to model satisfactorily the system KOI-126, finding consistent
  solutions for the radii and surface temperatures of all three
  components, using a solar-like value of the mixing-length parameter α
  in the convection zone and PHOENIX NextGen 1D model atmospheres for the
  surface boundary conditions. Depending on the chemical composition,
  we estimate the age of the system to be in the range 3-5 Gyr. For
  CM Draconis, on the other hand, we cannot reconcile our models with
  the observed radii and T<SUB>eff</SUB> using the current metal-poor
  composition estimate based on kinematics. Higher metallicities lessen
  but do not remove the discrepancy. We then explore the effect of varying
  the mixing-length parameter α. As previously noted in the literature,
  a reduced α can be used as a simple measure of the lower convective
  efficiency due to rotation and induced magnetic fields. Our models show
  a sensitivity to α (for α &lt; 1.0) sufficient to partially account
  for the radius discrepancies. It is, however, impossible to reconcile
  the models with the observations on the basis of the effect of the
  reduced α alone. We therefore suggest that the combined effects of
  high metallicity and α reduction could explain the observations of
  CM Draconis. For example, increasing the metallicity of the system
  towards super-solar values (i.e. Z= 2 Z<SUB>⊙</SUB>) yields an
  agreement within 2σ with α= 1.0.

Title: Modeling Kepler Observations of Solar-like Oscillations in
    the Red Giant Star HD 186355
Authors: Jiang, C.; Jiang, B. W.; Christensen-Dalsgaard, J.; Bedding,
   T. R.; Stello, D.; Huber, D.; Frandsen, S.; Kjeldsen, H.; Karoff, C.;
   Mosser, B.; Demarque, P.; Fanelli, M. N.; Kinemuchi, K.; Mullally, F.
Bibcode: 2011ApJ...742..120J
Altcode: 2011arXiv1109.0962J
  We have analyzed oscillations of the red giant star HD 186355
  observed by the NASA Kepler satellite. The data consist of the first
  five quarters of science operations of Kepler, which cover about 13
  months. The high-precision time-series data allow us to accurately
  extract the oscillation frequencies from the power spectrum. We find
  that the frequency of the maximum oscillation power, ν<SUB>max</SUB>,
  and the mean large frequency separation, Δν, are around 106 and
  9.4 μHz, respectively. A regular pattern of radial and non-radial
  oscillation modes is identified by stacking the power spectra
  in an echelle diagram. We use the scaling relations of Δν and
  ν<SUB>max</SUB> to estimate the preliminary asteroseismic mass,
  which is confirmed with the modeling result (M = 1.45 ± 0.05 M
  <SUB>⊙</SUB>) using the Yale Rotating stellar Evolution Code
  (YREC7). In addition, we constrain the effective temperature,
  luminosity, and radius from comparisons between observational
  constraints and models. A number of mixed l = 1 modes are also
  detected and taken into account in our model comparisons. We find
  a mean observational period spacing for these mixed modes of about
  58 s, suggesting that this red giant branch star is in the shell
  hydrogen-burning phase.

Title: Variation in convective properties across the HR diagram
Authors: Tanner, Joel; Basu, Sarbani; Demarque, Pierre; Robinson, Frank
Bibcode: 2011IAUS..271..401T
Altcode:
  We perform 3D radiative hydrodynamic simulations to study convection
  in low-mass main-sequence stars with the aim of improving stellar
  models. Comparing models from a 0.90 M<SUB>solar</SUB> evolutionary
  track with 3D simulations reveals distinct differences between
  simulations and mixing length theory. The simulations show obvious
  structural differences throughout the superadiabatic layer where
  convection is inefficient at transporting energy. The discrepancy
  between MLT and simulation changes as the star evolves and the dynamical
  effects of turbulence increase. Further, the simulations reveal a
  T-tau relation that is sensitive to the strength of the turbulence,
  which is in contrast to 1D stellar models that use the same T-tau
  relation across the HR diagram.

Title: Evolutionary scenarios and chemical inhomogeneities of extended
    horizontal branch stars
Authors: Esch, Lisa; Demarque, Pierre; Basu, Sarbani
Bibcode: 2011JPhCS.271a2039E
Altcode:
  Extended Horizontal Branch (EHB) stars are observed in many globular
  clusters and as field stars in the Galactic halo. They belong to old
  stellar populations of the halo and the old disk. Their evolutionary
  status is unclear, and still a current subject of debate. Current
  interest in these stars arise from their association with the
  discoveries of helium abundance inhomogeneities in the globular
  clusters ω Cen and NGC 2808. The origin of the inhomogeneities is not
  yet understood, but there are many interpretations. <P />In order to
  better understand EHB stars, we explore the evolution of standard
  blue Horizontal Branch (HB) models using up-to-date physics. We
  present several grids of post Zero Age Horizontal Branch (post-ZAHB)
  evolutionary models to include both canonical and non-canonical
  evolutionary scenarios, as well as to compare models that contain
  semi-convection to models without semi-convection. We follow the models
  to the termination of nuclear helium burning. The detailed properties of
  the models, including shell flashes and breathing pulses, are described.

Title: Characterizing Convection in Stellar Atmospheres
Authors: Tanner, Joel; Basu, Sarbani; Demarque, Pierre; Robinson, Frank
Bibcode: 2011JPhCS.271a2080T
Altcode:
  We perform 3D radiative hydrodynamic simulations to study the properties
  of convection in the superadiabatic layer of stars. The simulations
  show differences in both the stratification and turbulent quantities
  for different types of stars. We extract turbulent pressure and eddy
  sizes, as well as the T-τ relation for different stars and find that
  they are sensitive to the energy flux and gravity. We also show that
  contrary to what is usually assumed in the field of stellar atmospheres,
  the structure and gas dynamics of simulations of turbulent atmospheres
  cannot be parameterized with T<SUB>eff</SUB> and log(g) alone.

Title: Solar-like oscillations in cluster stars
Authors: Stello, D.; Basu, S.; Bedding, T. R.; Brogaard, K.; Bruntt,
   H.; Chaplin, W. J.; Christensen-Dalsgaard, J.; Demarque, P.; Elsworth,
   Y. P.; García, R. A.; Gilliland, R. L.; Hekker, S.; Huber, D.;
   Karoff, C.; Kjeldsen, H.; Lebreton, Y.; Mathur, S.; Meibom, S.;
   Molenda-Żakowicz, J.; Noels, A.; Roxburgh, I. W.; Silva Aguirre,
   V.; Sterken, C.; Szabó, R.
Bibcode: 2010AN....331..985S
Altcode: 2010arXiv1007.0009S
  This article summaries a talk given at the HELAS IV international
  meeting We present a brief overview of the history of attempts to
  obtain a clear detection of solar-like oscillations in cluster stars,
  and discuss the results on the first clear detection, which was made
  by the Kepler Asteroseismic Science Consortium (KASC) Working Group
  2. <P />Data from Kepler.

Title: 2D solar modeling
Authors: Ventura, P.; Penza, V.; Li, L.; Sofia, S.; Basu, S.;
   Demarque, P.
Bibcode: 2010Ap&SS.328..295V
Altcode: 2009Ap&SS.tmp..271V; 2009Ap&SS.tmp..283V; 2009arXiv0912.4998V
  Understanding the reasons of the cyclic variation of the total
  solar irradiance is one of the most challenging targets of modern
  astrophysics. These studies prove to be essential also for a more
  climatologic issue, associated to the global warming. Any attempt to
  determine the solar components of this phenomenon must include the
  effects of the magnetic field, whose strength and shape in the solar
  interior are far from being completely known. Modeling the presence
  and the effects of a magnetic field requires a 2D approach, since the
  assumption of radial symmetry is too limiting for this topic. We present
  the structure of a 2D evolution code that was purposely designed for
  this scope; rotation, magnetic field and turbulence can be taken into
  account. Some preliminary results are presented and commented.

Title: Detection of Solar-like Oscillations from Kepler Photometry
    of the Open Cluster NGC 6819
Authors: Stello, Dennis; Basu, Sarbani; Bruntt, Hans; Mosser, Benoît;
   Stevens, Ian R.; Brown, Timothy M.; Christensen-Dalsgaard, Jørgen;
   Gilliland, Ronald L.; Kjeldsen, Hans; Arentoft, Torben; Ballot,
   Jérôme; Barban, Caroline; Bedding, Timothy R.; Chaplin, William
   J.; Elsworth, Yvonne P.; García, Rafael A.; Goupil, Marie-Jo;
   Hekker, Saskia; Huber, Daniel; Mathur, Savita; Meibom, Søren;
   Sangaralingam, Vinothini; Baldner, Charles S.; Belkacem, Kevin;
   Biazzo, Katia; Brogaard, Karsten; Suárez, Juan Carlos; D'Antona,
   Francesca; Demarque, Pierre; Esch, Lisa; Gai, Ning; Grundahl, Frank;
   Lebreton, Yveline; Jiang, Biwei; Jevtic, Nada; Karoff, Christoffer;
   Miglio, Andrea; Molenda-Żakowicz, Joanna; Montalbán, Josefina; Noels,
   Arlette; Roca Cortés, Teodoro; Roxburgh, Ian W.; Serenelli, Aldo M.;
   Silva Aguirre, Victor; Sterken, Christiaan; Stine, Peter; Szabó,
   Robert; Weiss, Achim; Borucki, William J.; Koch, David; Jenkins, Jon M.
Bibcode: 2010ApJ...713L.182S
Altcode: 2010arXiv1001.0026S
  Asteroseismology of stars in clusters has been a long-sought goal
  because the assumption of a common age, distance, and initial chemical
  composition allows strong tests of the theory of stellar evolution. We
  report results from the first 34 days of science data from the Kepler
  Mission for the open cluster NGC 6819—one of the four clusters in
  the field of view. We obtain the first clear detections of solar-like
  oscillations in the cluster red giants and are able to measure
  the large frequency separation, Δν, and the frequency of maximum
  oscillation power, ν<SUB>max</SUB>. We find that the asteroseismic
  parameters allow us to test cluster membership of the stars, and
  even with the limited seismic data in hand, we can already identify
  four possible non-members despite their having a better than 80%
  membership probability from radial velocity measurements. We are also
  able to determine the oscillation amplitudes for stars that span about
  2 orders of magnitude in luminosity and find good agreement with the
  prediction that oscillation amplitudes scale as the luminosity to the
  power of 0.7. These early results demonstrate the unique potential of
  asteroseismology of the stellar clusters observed by Kepler.

Title: Calculation of Solar p-Mode Oscillation Frequency Splittings
    Based on a Two-Dimensional Solar Model
Authors: Li, L.; Basu, S.; Sofia, S.; Demarque, P.
Bibcode: 2009ASPC..416..321L
Altcode: 2008arXiv0810.4943L
  We compute the p-mode oscillation frequencies and frequency splittings
  that arise in a two-dimensional model of the Sun that contains toroidal
  magnetic fields in its interior.

Title: Direct Calculation of Turbulent Dissipation in Convective Zones
Authors: Penev, Kaloyan; Barranco, J.; Sasselov, D.; Robinson, F.;
   Demarque, P.
Bibcode: 2009AAS...21361205P
Altcode:
  The current understanding of the turbulent dissipation in stellar
  convective zones is based on the assumption that the turbulence
  follows Kolmogorov scaling. This assumption is valid for some cases
  in which the time frequency of the external shear is high (e.g. solar
  p-modes). However, for many cases of astrophysical interest (e.g. binary
  orbits, stellar pulsations e.t.c.) the timescales of interest
  lie outside the regime of applicability of Kolmogorov scaling. <P
  />We present direct calculations of the dissipation efficiency of
  the turbulent convective flow in this regime using simulations of
  anelastic convection with external forcing. We show that the effects
  of the turbulent flow are well represented by an effective viscosity
  coefficient and we provide the values of the effective viscosity as
  a function of the perturbation frequency. In addition we justify a
  perturbative method for finding the effective viscosity (proposed by
  Goodman and Oh 1997) and apply it to actual simulations of the surface
  convective zones of low mass stars.

Title: Comparing Properties of Convection in the Surface Layers of
    Stars With Different Masses and Evolutionary States
Authors: Robinson, F.; Tanner, J.; Basu, S.; Demarque, P.
Bibcode: 2009ASPC..416..357R
Altcode:
  By comparing convective properties computed from simulations derived
  from a series of G and K type stellar models, we find marked differences
  between simulations and mixing length theory. These differences
  increase with the strength of the turbulence (as measured by the size
  of the turbulent pressure). Two of the most obvious differences are
  in the run of the superadiabaticity versus depth and in the size of
  the convective eddies. Provided the turbulence is weak (i.e. the ratio
  of turbulent pressure to gas pressure is a few percent) the estimate
  of eddy size used in a stellar model eddy (i.e. αH<SUB>p</SUB>) is
  quite close to the mean size of the simulated eddies. However, as the
  strength of the turbulence is increased (as happens in more evolved
  or hotter or more massive stars) the mixing length estimate becomes a
  very poor approximation to the actual eddy size. We also show results
  of a comparison study between different simulation codes conducted by
  an independent collaborator. Despite significant differences in input
  physics, numerical methods and treatments of radiation, the resolved
  convective quantities differ by less than 10%.

Title: Dissipation Efficiency in Turbulent Convective Zones in
    Low-Mass Stars
Authors: Penev, K.; Sasselov, D.; Robinson, F.; Demarque, P.
Bibcode: 2009ApJ...704..930P
Altcode: 2008arXiv0810.5145P
  We extend the analysis of Penev et al. to calculate effective
  viscosities for the surface convective zones of three main-sequence
  stars of 0.775 M <SUB>sun</SUB>, 0.85 M <SUB>sun</SUB>, and the
  present day Sun. In addition, we also pay careful attention to all
  normalization factors and assumptions in order to derive actual
  numerical prescriptions for the effective viscosity as a function
  of the period and direction of the external shear. Our results are
  applicable for periods that are too long to correspond to eddies
  that fall within the inertial subrange of Kolmogorov scaling, but
  no larger than the convective turnover time, when the assumptions of
  the calculation break down. We find moderately anisotropic viscosity,
  scaling linearly with the period of the external perturbation, with
  its components having magnitudes between three and ten times smaller
  than the Zahn's prescription.

Title: Evolutionary Status of 85 Pegasi
Authors: Bach, K.; Lee, J.; Demarque, P.; Kim, Y. -C.
Bibcode: 2009ApJ...703..362B
Altcode:
  We have investigated the evolutionary status of the visual binary 85
  Peg (HD 224930) using a high-resolution spectroscopic analysis and
  the astrometric calibration of the stellar parameters. In spite of
  well-determined stellar parameters from HIPPARCOS astrometry and from
  spectroscopy, 85 Peg has for a long time revealed peculiar properties
  when attempts have been made to combine an evolutionary model with
  observation. There has been a chronic problem of the mass ratio of
  the two components when comparing 85 Peg's dynamical properties to the
  photometric magnitude difference. Moreover, 85 Peg has been suspected
  to have unique characteristics in its chemical composition. In order
  to determine accurate spectroscopic abundances, we have obtained
  high-resolution echelle spectra for 85 Peg. From our elemental analysis,
  we found that 85 Peg is α-enhanced with respect to the scaled solar
  abundance by a factor of 2. We then produced, within the framework of
  the standard stellar theory, grids of stellar model using the most
  recent observational results. To avoid many-fold degeneracy among
  physical quantities, a statistical minimization test was carried out
  between theoretical model grids. Enforcing consistency between the
  modeling and statistical constraints, we derived a reliable set of
  physical parameters and confirmed the trinarity of the system. In the
  context of asteroseismology, the theoretical frequency spectrum of 85
  Peg was calculated. 85 Peg A is expected to have a first order spacing
  Δν ~ 165 μHz at the reference frequency ν<SUB>0</SUB> = 790 μHz.

Title: Asteroseismology and interferometry of the red giant star
    ɛ Ophiuchi
Authors: Mazumdar, A.; Mérand, A.; Demarque, P.; Kervella, P.; Barban,
   C.; Baudin, F.; Coudé du Foresto, V.; Farrington, C.; Goldfinger,
   P. J.; Goupil, M. -J.; Josselin, E.; Kuschnig, R.; McAlister,
   H. A.; Matthews, J.; Ridgway, S. T.; Sturmann, J.; Sturmann, L.;
   ten Brummelaar, T. A.; Turner, N.
Bibcode: 2009A&A...503..521M
Altcode: 2009arXiv0906.3386M
  The GIII red giant star ɛ Oph has been found to exhibit several
  modes of oscillation by the MOST mission. We interpret the observed
  frequencies of oscillation in terms of theoretical radial p-mode
  frequencies of stellar models. Evolutionary models of this star,
  in both shell H-burning and core He-burning phases of evolution, are
  constructed using as constraints a combination of measurements from
  classical ground-based observations (for luminosity, temperature,
  and chemical composition) and seismic observations from MOST. Radial
  frequencies of models in either evolutionary phase can reproduce the
  observed frequency spectrum of ɛ Oph almost equally well. The best-fit
  models indicate a mass in the range of 1.85 ± 0.05 {M_⊙} with radius
  of 10.55 ± 0.15{R_⊙}. We also obtain an independent estimate of the
  radius of ɛ Oph with highly accurate interferometric observations in
  the infrared K' band, using the CHARA/FLUOR instrument. The measured
  limb-darkened disk angular diameter of ɛ Oph is 2.961 ± 0.007
  mas. Together with the Hipparcos parallax, this translates into a
  photospheric radius of R = 10.39 ± 0.07 {R_⊙}. The radius obtained
  from the asteroseismic analysis matches the interferometric value quite
  closely even though the radius was not constrained during the modelling.

Title: Isochrones for late-type stars
Authors: Demarque, Pierre
Bibcode: 2009IAUS..258..383D
Altcode:
  A brief summary of the history of stellar evolution theory and
  the use of isochrones is given. The present state of the subject
  is summarized. The major uncertainties in isochrone construction
  are considered: chemical abundances and color calibrations, and the
  treatment of turbulent convection in stellar interior and atmosphere
  models. The treatment of convection affects the modeling of stellar
  interiors principally in two ways: convective core overshoot which
  increases evolutionary lifetimes, and the depth of convection zones
  which determines theoretical radii. Turbulence also modifies atmospheric
  structure and dynamics, and the derivation of stellar abundances. The
  symbiosis of seismic techniques with increasingly more realistic
  three-dimensional radiation hydrodynamics simulations is transforming
  the study of late-type stars. The important case of very low mass stars,
  which are fully convective, is briefly visited.

Title: Two-Dimensional Stellar Evolution Code Including Arbitrary
    Magnetic Fields. II. Precision Improvement and Inclusion of Turbulence
    and Rotation
Authors: Li, Linghuai; Sofia, Sabatino; Ventura, Paolo; Penza,
   Valentina; Bi, Shaolan; Basu, Sarbani; Demarque, Pierre
Bibcode: 2009ApJS..182..584L
Altcode: 2008arXiv0810.4938L
  In the second paper of this series we pursue two objectives. First,
  in order to make the code more sensitive to small effects, we remove
  many approximations made in Paper I. Second, we include turbulence and
  rotation in the two-dimensional framework. The stellar equilibrium
  is described by means of a set of five differential equations, with
  the introduction of a new dependent variable, namely the perturbation
  to the radial gravity, that is found when the nonradial effects are
  considered in the solution of the Poisson equation. Following the
  scheme of the first paper, we write the equations in such a way that
  the two-dimensional effects can be easily disentangled. The key concept
  introduced in this series is the equipotential surface. We use the
  underlying cause-effect relation to develop a recurrence relation to
  calculate the equipotential surface functions for uniform rotation,
  differential rotation, rotation-like toroidal magnetic fields, and
  turbulence. We also develop a more precise code to numerically solve
  the two-dimensional stellar structure and evolution equations based on
  the equipotential surface calculations. We have shown that with this
  formulation we can achieve the precision required by observations by
  appropriately selecting the convergence criterion. Several examples are
  presented to show that the method works well. Since we are interested
  in modeling the effects of a dynamo-type field on the detailed envelope
  structure and global properties of the Sun, the code has been optimized
  for short timescales phenomena (down to 1 yr). The time dependence of
  the code has so far been tested exclusively to address such problems.

Title: VizieR Online Data Catalog: Velocities and photometry in NGC
    2112 (Carraro+, 2008)
Authors: Carraro, G.; Villanova, S.; Demarque, P.; Moni Bidin, C.;
   McSwain, M. V.
Bibcode: 2009yCat..73861625C
Altcode:
  U, B, V and I images centred on NGC 2112 were obtained at the Cerro
  Tololo Inter-American Observatory 1.0-m telescope, which is operated by
  the SMARTS1 consortium. The telescope is equipped with a new 4000x4000
  CCD camera having a pixel scale of 0.289arcsec/pixel, which allows
  one to cover a field of 20x20arcmin<SUP>2</SUP>. This allows us
  to cover the entire cluster, which has an estimated diameter of 18
  arcmin (Dias et al., 2002, Cat. &lt;VII/229&gt;). Observations were
  carried out on 2005 November 30. <P />Medium-resolution spectroscopic
  observations were carried out on the night of 2006 February 15 (Julian
  Date 2453783.57006) with the Hydra spectrograph onboard the Wisconsin
  Indiana Yale NOAO (WIYN) telescope at Kitt Peak National Observatory
  <P />Echelle spectrograms of stars 535, 261, 717, 304 and 836 were
  obtained on 2007 October 29 with the Magellan Inamori Kyocera Echelle
  (MIKE) spectrograph mounted on the Nasmyth focus of Landon Clay 6.5-m
  telescope at the Magellan Observatory. Data were obtained with both
  the blue and red arms. <P />(1 data file).

Title: Dissipation Efficiency of Turbulent Convection
Authors: Penev, Kaloyan; Sasselov, D.; Barranco, J.; Demarque, P.;
   Robinson, F.
Bibcode: 2009AAS...21431402P
Altcode:
  The turbulent flow in stellar convective zones is believed to be an
  important dissipation mechanism for phenomena like tides and stellar
  pulsations. The current understanding of this dissipation is based on
  the assumption that the turbulence follows Kolmogorov scaling. This
  assumption is reasonable for external shear with high time frequency
  (e.g. solar p-modes). However, for many cases of astrophysical interest
  (e.g. binary orbits, Cepheid pulsations etc.) the relevant timescales
  fall outside of the inertial subrange. We present direct calculations
  of the turbulent dissipation derived from simulations of stratified
  anelastic convection with external shear built directly into the
  equations of motion. We show that the observed dissipation is well
  parametrized as an effective viscosity coefficient and we derive the
  values of this coefficient as a function of the forcing period and
  the direction and amplitude of the shear. In addition we justify a
  perturbative method for finding the effective viscosity (proposed by
  Gooman and Oh. 1997) and use it to estimate the effective viscosity in
  the surface convective zones of low mass stars, using fully compressible
  numerical simulations with realistic physics specific to such stars.

Title: New Yonsei-Yale (Y <SUP>2</SUP>) Isochrones and
    Horizontal-Branch Evolutionary Tracks with Helium Enhancements
Authors: Han, S. -I.; Kim, Y. -C.; Lee, Y. -W.; Yi, S. K.; Kim,
   D. -G.; Demarque, P.
Bibcode: 2009gcgg.book...33H
Altcode:
  Recent studies [4,8,7,9,3] suggest that peculiar features observed
  in the horizontal-branch (HB) and main-squence (MS) of some Globular
  Clusters (GCs) are naturally reproduced by the presence of super-He-rich
  populations. However, there are no isochrones and self-consistent HB
  tracks available in the literature that are based on the up-to-date
  input physics and wide ranges of He and metal abundances. Here we
  present new sets of Y <SUP>2</SUP> isochrones and HB evolutionary
  tracks with the effects of He enhancements. The most up-to-date input
  physics are adopted, and the effects of α-enhancements ([α/Fe]=0.3)
  are also fully taken into account. These isochrones and tracks have been
  constructed for more realistic evolutionary population syntheses for
  old stellar populations, such as GCs and elliptical galaxies. The new
  isochrones and HB tracks well reproduce the observed color magnitude
  diagrams of Galactic GCs, including peculiar features observed in the
  HB and MS of ω Centauri and NGC 2808.

Title: The Nature of p-Modes and Granulation in Procyon: New MOST
    Photometry and New Yale Convection Models
Authors: Guenther, D. B.; Kallinger, T.; Gruberbauer, M.; Huber, D.;
   Weiss, W. W.; Kuschnig, R.; Demarque, P.; Robinson, F.; Matthews,
   J. M.; Moffat, A. F. J.; Rucinski, S. M.; Sasselov, D.; Walker,
   G. A. H.
Bibcode: 2008ApJ...687.1448G
Altcode:
  We present new photometry of Procyon, obtained by MOST during a 38
  day run in 2007, and frequency analyses of those data. The long time
  coverage and low point-to-point scatter of the light curve yield an
  average noise amplitude of about 1.5-2.0 ppm in the frequency range
  500-1500 μHz. This is half the noise level obtained from each of the
  previous two Procyon campaigns by MOST in 2004 and 2005. The 2007 MOST
  amplitude spectrum shows some evidence for p-mode signal: excess power
  centered near 1000 μHz and an autocorrelation signal near 55 μHz
  (suggestive of a mode spacing around that frequency), both consistent
  with p-mode model predictions. However, we do not see regularly spaced
  frequencies aligned in common l-valued ridges in echelle diagrams of
  the most significant peaks in the spectrum unless we select modes
  from the spectrum using a priori assumptions. The most significant
  peaks in the spectrum are scattered by more than ±5 μHz about the
  predicted l-valued ridges, a value that is consistent with the scatter
  among individually identified frequencies obtained from ground-based
  radial velocity (RV) observations. We argue that the observed scatter
  is intrinsic to the star, due to short lifetimes of the modes and
  the dynamic structure of Procyon's thin convection zone. We compare
  the MOST Procyon amplitude and power density spectra with preliminary
  results of three-dimensional numerical models of convection by the Yale
  group. These models show that, unlike in the Sun, Procyon's granulation
  signal in luminosity has a peak coinciding with the expected frequency
  region for p-modes near 1000 μHz. <P />Based on data from the MOST
  satellite, a Canadian Space Agency mission, jointly operated by Dynacon,
  Inc., the University of Toronto Institute of Aerospace Studies, and the
  University of British Columbia, with the assistance of the University
  of Vienna.

Title: The Y<SUP>2</SUP> Isochrones Getting an Extra Dimension
Authors: Yi, Sukyoung K.; Kim, Yong-Cheol; Demarque, Pierre; Lee,
   Young-Wook; Han, Sang-Il; Kim, Do Gyun
Bibcode: 2008IAUS..252..413Y
Altcode:
  The Yonsei-Yale Isochrones have been widely used since its birth
  in 2001. We announce a major upgrade mainly making varieties of
  helium values available. The recent works on the globular clusters
  with extreme helium abundances have called for such a need. The new
  version of the Y<SUP>2</SUP> Isochrones are available for [α/Fe] = 0
  through 0.6, ΔY/ΔZ = 1.5 through 3.0, and extreme helium abundances
  (Y = normal 0.05, 0.1, 0.15, 0.2), and for 11 metallicity grids, with
  full capability of interpolation. The database will be powerful for
  making population models. Besides, the accuracy of the models on the
  lower main sequence has been substantially improved. We illustrate
  the major upgrades and demonstrate the power of the new grids.

Title: YREC: the Yale rotating stellar evolution code. Non-rotating
    version, seismology applications
Authors: Demarque, P.; Guenther, D. B.; Li, L. H.; Mazumdar, A.;
   Straka, C. W.
Bibcode: 2008Ap&SS.316...31D
Altcode: 2007Ap&SS.tmp..447D; 2007arXiv0710.4003D
  The stellar evolution code YREC is outlined with emphasis on its
  applications to helio- and asteroseismology. The procedure for
  calculating calibrated solar and stellar models is described. Other
  features of the code such as a non-local treatment of convective
  core overshoot, and the implementation of a parametrized description
  of turbulence in stellar models, are considered in some detail. The
  code has been extensively used for other astrophysical applications,
  some of which are briefly mentioned at the end of the paper.

Title: The old open cluster NGC 2112: updated estimates of fundamental
    parameters based on a membership analysis†
Authors: Carraro, G.; Villanova, S.; Demarque, P.; Moni Bidin, C.;
   McSwain, M. V.
Bibcode: 2008MNRAS.386.1625C
Altcode: 2008arXiv0802.3243C; 2008MNRAS.tmp..416C
  We report on a new, wide-field (20 × 20 arcmin<SUP>2</SUP>),
  multicolour (UBVI), photometric campaign in the area of the nearby old
  open cluster NGC 2112. At the same time, we provide medium-resolution
  spectroscopy of 35 (and high-resolution of additional 5) red giant and
  turn-off stars. This material is analysed with the aim to update the
  fundamental parameters of this traditionally difficult cluster, which
  is very sparse and suffers from heavy field star contamination. Among
  the 40 stars with spectra, we identified 21 bona fide radial velocity
  members which allow us to put more solid constraints on the cluster's
  metal abundance, long suggested to be as low as the metallicity of
  globulars. As indicated earlier by us on a purely photometric basis,
  the cluster [Fe/H] abundance is slightly supersolar ([Fe/H] = 0.16
  +/- 0.03) and close to the Hyades value, as inferred from a detailed
  abundance analysis of three of the five stars with higher resolution
  spectra. Abundance ratios are also marginally supersolar. <P />Based on
  this result, we revise the properties of NGC 2112 using stellar models
  from the Padova and Yale-Yonsei groups. <P />For this metal abundance,
  we find that the cluster's age, reddening and distance values are 1.8
  Gyr, 0.60 mag and 940 pc, respectively. Both the Yale-Yonsei and Padova
  models predict the same values for the fundamental parameters within
  the errors. <P />Overall, NGC 2112 is a typical solar neighbourhood,
  thin-disc star cluster, sharing the same chemical properties of F-G
  stars and open clusters close to the Sun. <P />This investigation
  outlines the importance of a detailed membership analysis in the study
  of disc star clusters. <P />This paper includes data gathered with
  the 6.5 Magellan Telescopes, located at Las Campanas Observatory,
  Chile. <P />The data discussed in this paper will be made available
  at the WEBDA open cluster data base http://www.univie.ac.at/webda,
  which is maintained by E. Paunzen and J.-C. Mermilliod. ‡
  <P />E-mail: gcarraro@eso.org (GC); sandro.villanova@unipd.it
  (SV); demarque@astro.yale.edu (PD); mbidin@das.uchile.cl (CMB);
  mcswain@lehigh.edu(MVM)

Title: Effects of Chemical Abundances on the Structure and Dynamics
    of the Solar Atmosphere
Authors: Demarque, Pierre; Basu, S.; Robinson, F.; Hunter, C.;
   Kallinger, T.
Bibcode: 2008AAS...212.1707D
Altcode: 2008BAAS...40..211D
  This paper presents a comparison between two three-dimensional
  radiative hydrodynamical (3D RHD) simulations of the solar outer
  layers using the Grevesse &amp; Sauval (1998; GS98) and the Asplund,
  Grevesse &amp; Sauval (2005; AGS05) mixtures, respectively. <P />The
  AGS05 mixture is a revision of the solar abundance mixture using
  a model atmosphere based on the stratification and dynamics of a
  solar 3D RHD simulation performed with the GS98 mixture, using the
  code of Stein &amp; Nordlund (1989, 1998). Our simulations use the
  same code, and physically realistic treatment of radiative opacities
  and equation of state as Robinson et al. (2003). <P />A comparison
  between our GS98 and AGS05 3D simulations shows differences both in
  the mean vertical temperature gradient and in the turbulent velocity
  field in the line forming region of the solar atmosphere. The whole
  superadiabatic layer (SAL) in the AGS05 simulation, including its peak,
  is shifted outward with respect to the GS98 SAL. Turbulent velocities,
  critical for absorption line profile calculations, are larger in the
  AGS05 simulation by about 10%. Since opacities for the AGS05 mixture
  are lower than those for the GS98 mixture, the T-τ relations derived
  from the two simulations are different. At 5000K, τ obtained from the
  GS98 simulation is about 30% larger than that obtained from the AGS05
  simulation. <P />These results show the importance of preserving self
  consistency in the chemical abundances between the model atmosphere
  and the 3D HRD simulation. When deriving the solar abundances,
  one must iterate the chemical composition in the model atmosphere,
  and hence in the 3D simulation on which the atmosphere is based. <P
  />This research was supported in part by NASA/ATP grant NAG5-13299
  (PD and FR) and NSF grant ATM 0348837 to SB.

Title: A cgi synthetic CMD calculator for the YY Isochrones
Authors: Demarque, P.; Virani, S. N.; Murphy, E. J.; Woo, J. -H.;
   Kim, Y. -C.; Yi, S. K.
Bibcode: 2008arXiv0801.0451D
Altcode:
  We describe a web-based cgi calculator for constructing synthetic
  color-magnitude diagrams for a simple stellar population (SSP) using
  the Yonsei-Yale (YY) isochrone data base. This calculator is designed
  to be used interactively. It creates quick look CMD displays in (B-V)
  and (V-I) colors. Stochastic effects on the CMDs are included. Output
  in tabular form is also provided for special purpose displays, or for
  combining the CMDs of different stellar populations. This research
  tool has applications in studies of the stellar content of our Galaxy
  and external systems. It provides an easy way to interpret the CMDs
  in resolved stellar populations. It offers the means to explore the
  dependence of the integrated properties of unresolved stellar systems
  on stellar parameters (ages, chemical composition, binarity) and on the
  characteristics of their parent population (IMF slope and mass range).

Title: Turbulent Convection in Stars: Some Recent Advances
Authors: Demarque, P.; Robinson, F. J.; Straka, C. W.
Bibcode: 2007ASPC..374...27D
Altcode:
  Advances are discussed in two areas in which improved numerical
  treatments of radiation hydrodynamics, coupled with advances in helio-
  and asteroseismology, provide stringent tests of stellar interior
  models. Stellar evolution data are fundamental building blocks
  in population studies. The first area is convective core overshoot
  which affects evolutionary timescales and the evolution of integrated
  spectral energy distributions in stellar systems. The second area is the
  treatment of radiation hydrodynamics in the outer layers of cool stars
  with convection zones, with the aim of removing the shortcomings of the
  canonical mixing-length theory. A realistic physical description is also
  needed to calculate p-mode excitation and amplitudes, tidal dissipation
  in convection zones, and to derive accurate chemical abundances.

Title: Surface Convection in Sun and a Population II Star
Authors: Jung, Y. K.; Kim, Y. -C.; Robinson, F. J.; Demarque, P.;
   Chan, K. L.
Bibcode: 2007ASPC..362..306J
Altcode:
  Three-dimensional hydrodynamic simulations including radiative energy
  transfer were performed to study the characteristics of surface
  convection in Sun and a population II star. To compare convection
  phenomenon of a Pop II star with that of the Sun, we have constructed
  a Pop II star whose mass is 0.7 solar mass and metallicity is z =
  0.0004. The domain of simulation is a rectangular box containing
  a convection-radiation transition region with an impenetrable
  boundary. The mass and the momentum are conserved. <P />The thermal and
  dynamic variables of each layer, including overshoot, were explored. We
  found that the effect of turbulence in a Pop II star is lower than
  that of Sun. The vertical and horizontal sizes of granules, dominantly
  affected by the turbulence, are also smaller in a Pop II star. These
  results indicate that a Pop II star has fewer turbulent structures
  than Sun because of its higher density and surface gravity.

Title: Probing turbulence with seismic observations of α Centauri
Authors: Straka, C. W.; Demarque, P.; Robinson, F. J.
Bibcode: 2007IAUS..239..388S
Altcode:
  No abstract at ADS

Title: Comparing convection in the Sun with Procyon A
Authors: Robinson, Frank; Demarque, Pierre
Bibcode: 2007IAUS..239..358R
Altcode:
  No abstract at ADS

Title: Calibration of Stellar Parameters of 85 Peg System
Authors: Bach, Kiehunn; Kim, Yong-Cheol; Demarque, Pierre
Bibcode: 2007JASS...24...31B
Altcode:
  We have investigated the evolutionary status of 85 Peg within the
  framework of standard evolutionary theory. 85 Peg has been known to be
  a visual and spectroscopic binary system in the solar neighborhood. In
  spite of the accurate information of the total mass (∼ 1.5 M_{⊙})
  and the distance (∼12pc) from the HIPPARCOS upshape parallax, it has
  been undetermined an individual mass, therefore the evolved status of
  the system. Moreover, the coupled uncertainties of chemical composition
  and age, make matters worse in predicting an evolutionary status of the
  system. Nevertheless, we computed the various possible models for 85
  Peg, and then calibrated stellar parameters by adjusting to the recent
  observational data. Our modelling computation has included recently
  updated input physics and stellar theory such as opacity, equation
  of state, and chemical diffusion. Through a statistical assessment,
  we have derived a confident parameter set as the best solution which
  minimized χ^2 within the observational error domain. Most of all, we
  found that 85 Peg is not a binary system but a triple system with an
  unseen companion 85 Peg B_{b}∼0.16M_{⊙}. The aim of the present
  paper is (1) to provide a complete modelling of the stellar system
  based on the evolutionary theory, and (2) to constrain the physical
  dimensions such as mass, metallicity and age.

Title: On Dissipation inside Turbulent Convection Zones from
    Three-dimensional Simulations of Solar Convection
Authors: Penev, Kaloyan; Sasselov, Dimitar; Robinson, Frank; Demarque,
   Pierre
Bibcode: 2007ApJ...655.1166P
Altcode: 2006astro.ph..7016P
  The development of two-dimensional and three-dimensional simulations of
  solar convection has lead to a picture of convection quite unlike the
  usually assumed Kolmogorov spectrum turbulent flow. We investigate the
  impact of this changed structure on the dissipation properties of the
  convection zone, parameterized by an effective viscosity coefficient. We
  use an expansion treatment developed by Goodman &amp; Oh, applied to a
  numerical model of solar convection, to calculate effective viscosity
  as a function of frequency and compare this to currently existing
  prescriptions based on the assumption of Kolmogorov turbulence. The
  results quite closely match a linear scaling with period, even though
  this same formalism applied to a Kolmogorov spectrum of eddies gives
  a scaling with a power-law index of 5/3.

Title: Short-Period Variables in the Local Group Dwarf Galaxies
    Tucana and LGS3
Authors: Bernard, E. J.; Monelli, M.; Gallart, C.; Aparicio, A.;
   Bertelli, G.; Cassisi, S.; Cole, A. A.; Demarque, P.; Dolphin, A. E.;
   Drozdovsky, I.; Ferguson, H. C.; Hidalgo, S.; Mateo, M.; Mayer, L.;
   Navarro, J.; Pont, F.; Skillman, E. D.; Stetson, P. B.; Tolstoy, E.
Bibcode: 2007astro.ph..1729B
Altcode:
  We present preliminary results concerning the search for short-period
  variable stars in Tucana and LGS3 based on very deep HST/ACS imaging. In
  the fraction of the observed field we studied in each galaxy, a total of
  133 and 30 variables were found, respectively. For Tucana, we identified
  76 of them as RR Lyrae (RRL) stars pulsating in the fundamental mode
  (RRab) and 32 in the first-overtone mode (RRc), as well as 2 anomalous
  Cepheids (AC). The mean period of the RRab and RRc is 0.59 and 0.35
  days, respectively. In the case of LGS3, we found 24 RRab and 4 RRc,
  with mean periods 0.61and 0.39 days, respectively, plus two candidate
  ACs. These values place both galaxies in the Oosterhoff gap.

Title: The hot stars in orbit around the M 31 central supermassive
black hole: are they young or old?
Authors: Demarque, P.; Virani, S.
Bibcode: 2007A&A...461..651D
Altcode: 2006astro.ph..3326D
  Aims:The cluster of hot stars observed in orbit around the central black
  hole of M 31 has been interpreted as a 200 Myr starburst. The formation
  of a population of young stars in close proximity to a massive black
  hole presents a difficult challenge to star formation theory. We point
  out that in a high stellar density environment, the course of stellar
  evolution is modified by frequent collisions and mergers. <BR />Methods:
  Blue stragglers, which are the results of mergers in globular clusters,
  occupy the same position in the color-magnitude diagram as the observed
  hot stars in M 31. For confirmation, the integrated spectrum of P3
  is shown to be compatible with the spectral energy distribution of
  a blue horizontal branch field star. <BR />Results: We suggest an
  old stellar population of evolved blue horizontal-branch stars and
  of merger products cannot be ruled out on the basis of the available
  data. Observations are suggested that would help distinguish between a
  "young" and "old" stellar population interpretation of the observations.

Title: Asteroseismic diagnostics of stellar convective cores
Authors: Mazumdar, A.; Basu, S.; Collier, B. L.; Demarque, P.
Bibcode: 2006ESASP.624E.109M
Altcode: 2006soho...18E.109M
  No abstract at ADS

Title: Asteroseismic diagnostics of stellar convective cores
Authors: Mazumdar, Anwesh; Basu, Sarbani; Collier, Braxton L.;
   Demarque, Pierre
Bibcode: 2006MNRAS.372..949M
Altcode: 2006astro.ph..8331M; 2006MNRAS.tmp.1010M
  We present a detailed study of the small frequency separations as
  diagnostics of the mass of the convective core and evolutionary stage
  of solar-type stars. We demonstrate how the small separations can be
  combined to provide sensitive tests for the presence of convective
  overshoot at the edge of the core. These studies are focused on
  low-degree oscillation modes, the only modes expected to be detected
  in distant stars. Using simulated data with realistic errors, we find
  that the mass of the convective core can be estimated to within 5 per
  cent if the total stellar mass is known. Systematic errors arising due
  to uncertainty in the mass could be up to 20 per cent. The evolutionary
  stage of the star, determined in terms of the central hydrogen abundance
  using our proposed technique, however, is much less sensitive to the
  mass estimate.

Title: NGC 6791: An Exotic Open Cluster or the Nucleus of a Tidally
    Disrupted Galaxy?
Authors: Carraro, Giovanni; Villanova, Sandro; Demarque, Pierre;
   McSwain, M. Virginia; Piotto, Giampaolo; Bedin, Luigi R.
Bibcode: 2006ApJ...643.1151C
Altcode: 2005astro.ph.12650C
  We report on high-resolution echelle spectroscopy of 20 giant stars
  in the Galactic old open cluster NGC 6791, obtained with Hydra at the
  WIYN telescope. High-precision radial velocity allows us to isolate
  15 bona fide cluster members. From 10 of them we derive a global
  [M/H]=+0.39+/-0.05. We therefore confirm that NGC 6791 is extremely
  metal-rich, exhibits a few marginally subsolar abundance ratios,
  and within the resolution of our spectra does not show evidence
  of spread in metal abundance. With these new data we rederive the
  fundamental cluster parameters, suggesting that it is about 8 Gyr old
  and 4.3 kpc from the Sun. The combination of its chemical properties,
  age, position, and Galactic orbit hardly makes NGC 6791 a genuine
  Population I open cluster. We discuss possible interpretations of
  the cluster peculiarities, suggesting that the cluster might be what
  remains of a much larger system whose initial potential well could
  have been sufficient to produce high-metallicity stars and which has
  been depopulated by the tidal field of the Galaxy. Alternatively,
  its current properties may be explained by the perturbation of the
  Galactic bar on an object that originated well inside the solar ring,
  where the metal enrichment was very fast.

Title: Dynamical Characteristics Of Surface Convection In The Sun
    And A Population II Star
Authors: Bach, Kiehunn; Jung, Y. K.; Kim, Y. C.; Robinson, F. J.;
   Demarque, P.; Chan, K. L.
Bibcode: 2006AAS...208.0602B
Altcode: 2006BAAS...38...84B
  We present the results of the 3 dimensional radiative hydrodynamic
  numerical large eddy simulations of the outer layers of stars. The
  goal of this study is to compare convection phenomenon of a Pop II star
  with the Sun. We have constructed a Pop II star of 0.7 solar mass and
  metallicity &lt;i&gt;z&lt;/i&gt;=0.0004. The results are compared to
  a similar simulation performed for the Sun using the same detailed
  physics input and numerical code. The domains of simulations extend
  from the observable atmospheric layers in radiative equilibrium and
  the outer layers of the convection zones, down to a depth at which
  the temperature gradient exceeds the adiabatic value by only a very
  small amount. Each simulation has been made for 32 and 24 minutes for
  the Sun and a Pop II star, respectively, and the thermal and dynamical
  structures of each star including overshoot are explored. The vertical
  and horizontal sizes of granules, dominantly affected by the turbulence,
  are smaller in a Pop II star. These results indicate that a Pop II
  star has less turbulent structures than that of the Sun because of
  its higher density distribution and surface gravity.

Title: Two-dimensional Stellar Evolution Code Including Arbitrary
    Magnetic Fields. I. Mathematical Techniques and Test Cases
Authors: Li, L. H.; Ventura, P.; Basu, S.; Sofia, S.; Demarque, P.
Bibcode: 2006ApJS..164..215L
Altcode: 2005astro.ph.11238L
  A high-precision two-dimensional stellar evolution code has
  been developed for studying solar variability due to structural
  changes produced by varying internal magnetic fields of arbitrary
  configurations. Specifically, we are interested in modeling the
  effects of a dynamo-type field on the detailed internal structure and
  on the global parameters of the Sun. The high precision is required to
  model both very small solar changes (of the order of 10<SUP>-4</SUP>)
  and short timescales (of the order of 1 yr). It is accomplished by
  using the mass coordinate to replace the radial coordinate, by using
  fixed and adjustable time steps, a realistic stellar atmosphere, and
  element diffusion, and by adjusting the grid points. We have also
  built into the code the potential to subsequently include rotation
  and turbulence. The current code has been tested for several cases,
  including its ability to reproduce the one-dimensional results.

Title: Turbulence in models of a star other than Sun: matching η
    Bootis observed p-modes
Authors: Straka, C. W.; Demarque, P.; Guenther, D. B.; Li, L.;
   Robinson, F. J.
Bibcode: 2006MmSAI..77..421S
Altcode:
  Standard stellar models for η Boo fail to reproduce the newly
  observed low frequency p-modes from space and the high frequency
  p-modes observed from the ground, simultaneously. This discrepancy
  can be removed by including turbulence in the modeling of the outer
  layers of η Boo. We include turbulence by applying the effects of
  turbulent pressure and turbulent kinetic energy -- extracted from a
  hydrodynamical 3D convection simulation for the Sun -- at the correct
  depth in the 1D models of η Boo.

Title: Space- and Ground-based Pulsation Data of η Bootis Explained
    with Stellar Models Including Turbulence
Authors: Straka, Christian W.; Demarque, Pierre; Guenther, D. B.;
   Li, Linghuai; Robinson, Frank J.
Bibcode: 2006ApJ...636.1078S
Altcode: 2005astro.ph..9403S
  The space telescope MOST is now providing us with extremely accurate
  low-frequency p-mode oscillation data for the star η Boo. We
  demonstrate in this paper that these data, when combined with
  ground-based measurements of the high-frequency p-mode spectrum,
  can be reproduced with stellar models that include the effects of
  turbulence in their outer layers. Without turbulence, the l=0 modes
  of our models deviate from either the ground-based or the space data
  by about 1.5-4 μHz. This discrepancy can be completely removed by
  including turbulence in the models, and we can exactly match 12 out
  of 13 MOST frequencies that we identified as l=0 modes, in addition
  to 13 out of 21 ground-based frequencies within their observational
  2 σ tolerances. The better agreement between model frequencies and
  observed frequencies depends for the most part on the turbulent kinetic
  energy that was taken from a three-dimensional convection simulation
  for the Sun.

Title: Turbulence in η  Bootis outer layers as derived from 3D
    convection simulations to explain its observed p-mode spectrum
Authors: Straka, C. W.; Demarque, P.; Robinson, F. J.; Guenther,
   D. B.; Li, L.
Bibcode: 2005AAS...207.6913S
Altcode: 2005BAAS...37Q1272S
  Standard stellar models for η Boo fail to reproduce the observed low
  frequency p-modes from space and the high frequency p-modes observed
  from ground, simultaneously. This discrepancy can be mitigated by
  including turbulence in the modeling of the outer layers of η Boo. We
  present new results of our full 3D turbulent convection simulation of
  η Boo's outer layers. With these simulations we are able to answer
  the question whether the discrepancy between models and observations
  can be fully attributed to the effects of turbulence. <P />This
  research was supported by NASA grant NAG5-13299, and in part by the
  NASA EOS/IDS program.

Title: Asteroseismic Diagnostics of Stellar Convective Cores
Authors: Mazumdar, A.; Collier, B. L.; Basu, S.; Demarque, P.
Bibcode: 2005AAS...207.6912M
Altcode: 2005BAAS...37.1272M
  The extent of the central convective region is one of the crucial
  factors that govern the structure and evolution of massive stars. It
  has been suggested that observations of seismic waves that penetrate
  the deepest layers of a star might be used to estimate the size
  of such convective cores. This would allow a rigorous test of the
  current theories of convection and stellar evolution. We investigate
  whether suitable diagnostics can be constructed from the frequencies
  of low degree modes of oscillation which are sensitive to the size and
  evolution of the stellar core. <P />SB and BC are partially supported
  in this research by grant ATM-0348837 from NSF. PD is supported by
  NASA grant NAG5-13299.

Title: The Nonhomologous Nature of Solar Diameter Variations
Authors: Sofia, Sabatino; Basu, Sarbani; Demarque, Pierre; Li,
   Linghuai; Thuillier, Gerard
Bibcode: 2005ApJ...632L.147S
Altcode: 2005astro.ph..9816S
  We show in this Letter that the changes of the solar diameter in
  response to variations of large-scale magnetic fields and turbulence
  are not homologous. For the best current model, the variation at
  the photospheric level is over 1000 times larger than the variation
  at a depth of 5 Mm, which is about the level at which f-mode solar
  oscillations determine diameter variations. This model is supported
  by observations that indicate larger diameter changes for high-degree
  f-modes than for low-degree f-modes, since the energy of the former
  is concentrated at shallower layers than the latter.

Title: Simulating the outer layers of Procyon A: a comparison with
    the Sun
Authors: Robinson, F. J.; Demarque, P.; Guenther, D. B.; Kim, Y. -C.;
   Chan, K. L.
Bibcode: 2005MNRAS.362.1031R
Altcode: 2005astro.ph..7005R; 2005MNRAS.tmp..730R
  We compare a new 3D radiative hydrodynamical simulation of the surface
  layers of Procyon A to a similar 3D simulation of the surface layers
  of the Sun. Both simulations include realistic input physics and are
  performed using the same numerical techniques and computer codes. <P
  />Convection in the surface layers of Procyon A is very different from
  the Sun. Compared with the Sun, the atmospheric structure and convective
  flow in Procyon A exhibit the following characteristics. (i) The highly
  superadiabatic transition layer (SAL) is located at a much shallower
  optical depth; it is in a dynamically active region and its outer
  region is sometimes located in the optically thin atmosphere. (ii)
  The outer region of the SAL moves from an optically thin region to
  a thick region and back again over a time of 20-30 min. This motion,
  which is driven by the granulation, takes place in a time approximately
  half the turnover time of the largest granules. (iii) The peak rms
  velocity in the vertical direction is much larger in Procyon A. The
  main reason for the radically different radiative-convective behaviour
  in Procyon A compared with the Sun is the role played by turbulent
  eddies in determining the overall flow/thermal structure. The turbulent
  pressure and turbulent kinetic energy can exceed 50 per cent of the
  local gas pressure (compared with about 10-20 per cent in the Sun). In
  such regions, the mixing lengthy theory is a poor approximation. <P
  />The Procyon A simulation thus reveals two distinct time-scales: the
  autocorrelation time of the vertical velocity and the characteristic
  time-scale of the SAL, which is tied to granulation. Just below the
  surface, the autocorrelation decay time is about 5 min in Procyon A
  and the SAL motion time-scale is 20-30 min. In the simulations, the
  peak value of the superadiabaticity varies between 0.5 and 3. When
  the SAL penetrates the optically thin region, there are efficient
  radiative losses and the peak of the SAL is low. We speculate that these
  losses damp out the relative amplitudes in luminosity (temperature
  fluctuations) compared with velocity (Doppler). Although this will
  not affect the frequencies of the peaks in the power spectrum, it
  will probably lower the average amplitude of the peaks relative to
  the noise background.

Title: Core Overshoot: An Improved Treatment and Constraints from
    Seismic Data
Authors: Straka, Christian W.; Demarque, Pierre; Guenther, D. B.
Bibcode: 2005ApJ...629.1075S
Altcode: 2005astro.ph..5009S
  We present a comprehensive set of stellar evolution models for Procyon A
  in an effort to guide future measurements of both traditional stellar
  parameters and seismic frequencies toward constraining the amount
  of core overshoot in Procyon A and possibly other stars. Current
  observational measurements of Procyon A when combined with traditional
  stellar modeling only place a large upper limit on overshoot of
  α<SUB>OV</SUB>&lt;1.1. By carrying out a detailed pulsation analysis,
  we further demonstrate how p- and g-mode averaged spacings can be used
  to gain better estimates of the core size. For both p- and g-modes, the
  frequency spacings for models without overshoot are clearly separated
  from the models with overshoot. In addition, measurements of the l=0
  averaged small p-mode spacings could be used to establish Procyon A's
  evolutionary stage. For a fixed implementation of overshoot and under
  favorable circumstances, the g-mode spacings can be used to determine
  the overshoot extent to an accuracy of +/-0.05H<SUB>P</SUB>. However,
  we stress that considerable confusion is added due to the unknown
  treatment of the overshoot region. This ambiguity might be removed by
  analyzing many different stars. A simple nonlocal convection theory
  developed by Kuhfuss is implemented in our stellar evolution code and
  contrasted with the traditional approaches. We show that this theory
  supports a moderate increase of the amount of convective overshoot
  with stellar mass of Δα<SUB>OV</SUB>~=+0.10 between 1.5 and 15
  M<SUB>solar</SUB>. This theory places an upper limit on Procyon A's
  core overshoot extent of ~0.4H<SUB>P</SUB>, which matches the limit
  imposed by Roxburgh's integral criterion.

Title: Numerical Simulation of the Outer Layers of Procyon A:
    a Comparison with the Sun
Authors: Demarque, P.; Robinson, F. J.; Guenther, D. B.; Kim, Y. -C.;
   Chan, K. L.
Bibcode: 2005AAS...206.3501D
Altcode: 2005BAAS...37..486D
  We present a 3D radiative-hydrodynamical simulation of the surface
  layers of Procyon A, and compare it to a similar simulation for the
  Sun. Procyon has a thin outer convection zone, and its atmosphere,
  like the solar atmosphere, is characterized by granulation. Procyon
  granules are much larger than in the Sun, with a mean diameter near
  10,000 km, in comparison with 1,200 km for a solar granule. The dynamics
  of the Procyon atmosphere differ from the solar atmosphere dynamics
  in fundamental ways: (1) the ratio of turbulent to gas pressure
  is larger in the Procyon atmosphere (2) the highly superadiabatic
  transition layer (SAL) is located at much shallower optical depth (3)
  the location of the SAL maximum moves back and forth in the atmosphere,
  from an optically thin to optically thick region in a quasi-periodic
  manner. This motion is driven by the penetration of granules into the
  outermost atmospheric layers while they overturn. The timescale of this
  phenomenon is roughly half the full granule lifetime (which is typically
  in the range of 40 to 60 minutes); (3) the maximum temperature contrast
  at a given optical depth varies rapidly on a short timescale resulting
  in locally large radiative losses and strong intensity contrasts (hot
  spots). The simulation also shows that the autocorrelation timescale
  in Procyon's atmosphere is favorable to the stochastic excitation of
  p-modes by turbulence. However highly efficient radiative damping
  in Procyon's atmosphere is likely to result in much shorter p-mode
  coherence lifetimes than in the Sun. <P />This research was supported
  in part by NASA grant NAG5-13299 (PD), the NASA EOS/IDS Program
  (FJR), NSERC of Canada (DBG) and the Korea Research Foundation grant
  KRF-2003-015-C00249 (YCK).

Title: Super-Helium-rich Populations and the Origin of Extreme
    Horizontal-Branch Stars in Globular Clusters
Authors: Lee, Young-Wook; Joo, Seok-Joo; Han, Sang-Il; Chung, Chul;
   Ree, Chang H.; Sohn, Young-Jong; Kim, Yong-Cheol; Yoon, Suk-Jin; Yi,
   Sukyoung K.; Demarque, Pierre
Bibcode: 2005ApJ...621L..57L
Altcode: 2005astro.ph..1500L
  Recent observations for the color-magnitude diagrams (CMDs) of
  the massive globular cluster ω Centauri have shown that it has a
  striking double main sequence (MS), with a minority population of
  bluer and fainter MS stars well separated from a majority population
  of MS stars. Here we confirm, with the most up-to-date Y<SUP>2</SUP>
  isochrones, that this special feature can only be reproduced by
  assuming a large variation (ΔY=0.15) of primordial helium abundance
  among several distinct populations in this cluster. We further show
  that the same helium enhancement required for this special feature on
  the MS can by itself reproduce the extreme horizontal-branch (HB) stars
  observed in ω Cen, which are hotter than normal HB stars. Similarly,
  the complex features on the HBs of other globular clusters, such
  as NGC 2808, are explained by large internal variations of helium
  abundance. Supporting evidence for the helium-rich population is
  also provided by the far-UV (FUV) observations of extreme HB stars in
  these clusters, where the enhancement of helium can naturally explain
  the observed fainter FUV luminosity for these stars. The presence of
  super-helium-rich populations in some globular clusters suggests that
  a third parameter, other than metallicity and age, also influences
  the CMD morphology of these clusters.

Title: Y<SUP>2</SUP> Isochrones with an Improved Core Overshoot
    Treatment
Authors: Demarque, Pierre; Woo, Jong-Hak; Kim, Yong-Cheol; Yi,
   Sukyoung K.
Bibcode: 2004ApJS..155..667D
Altcode:
  Convective core overshoot affects stellar evolution rates and the
  dating of stellar populations. In this paper, we provide a patch to
  the Y<SUP>2</SUP> isochrones with an improved treatment of convective
  core overshoot. The new tracks cover the transition mass range from no
  convective core to a fully developed convective core. We compare the
  improved isochrones to CMDs of a few well-observed open star clusters
  in the Galaxy and the Large Magellanic Cloud. Finally, we discuss
  future prospects for improving the treatment of core overshoot with
  the help of asteroseismology.

Title: a 2-D Stellar Evolution Code Including Arbitrary Magnetic
    Fields
Authors: Li, L.; Basu, S.; Sofia, S.; Demarque, P.
Bibcode: 2004ESASP.559..536L
Altcode: 2004soho...14..536L
  No abstract at ADS

Title: Solar Luminosity Variations may Occur on Short Time Scales
Authors: Li, L.; Basu, S.; Sofia, S.; Demarque, P.
Bibcode: 2004ESASP.559..544L
Altcode: 2004soho...14..544L
  No abstract at ADS

Title: a Radiation-Hydrodynamical Simulation of the Envelope of
    Procyon a
Authors: Robinson, F. J.; Demarque, P.; Kim, Y. -C.
Bibcode: 2004ESASP.559..602R
Altcode: 2004soho...14..602R
  No abstract at ADS

Title: Asteroseismic Determination of Helium Abundance in Solar-Type
    Stars
Authors: Basu, S.; Mazumdar, A.; Antia, H. M.; Demarque, P.
Bibcode: 2004ESASP.559..313B
Altcode: 2004soho...14..313B
  No abstract at ADS

Title: The Y <SUP>2</SUP> Isochrones
Authors: Yi, Sukyoung K.; Demarque, Pierre; Kim, Yong-Cheol
Bibcode: 2004Ap&SS.291..261Y
Altcode: 2004astro.ph..9024D
  We present a new set of isochrones in which the effect of the α-element
  enhancement is fully incorporated. The isochrone tables, together with
  interpolation routines in age and chemical composition, and in [α/Fe]
  are available on request as well as from the electronic version of
  our ApJ papers. Newly derived ages of Galactic globular clusters using
  these isochrones are 20 to 30% smaller than previous estimates.

Title: Convection in the envelope of Procyon A
Authors: Demarque, P.; Basu, S.; Guenther, D. B.; Li, L. H.; Robinson,
   F. J.
Bibcode: 2004AAS...204.0706D
Altcode: 2004BAAS...36R.785D
  Theoretical models are presented for the envelope of Procyon A. Procyon
  A is known to have a shallow convection zone. We investigate the
  depth of the convection zone, the efficiency of convection in the
  convection region, convective velocities and uncertainties in the
  efficiency of diffusion from the convection zone into the adjacent
  radiative layers. The effects of turbulent pressure and turbulent
  kinetic energy are included in the models, based on a parameterization
  of 3D simulations of radiative hydrodynamics. The conditions for
  the stochastic excitation of acoustic non-radial oscillations are
  investigated. <P />This work is supported in part by grants from NASA
  (PD, SB, FJR), NSF (SB, LHL) and NSERC (DBG).

Title: Asteroseismic determination of helium abundance in stellar
    envelopes
Authors: Basu, Sarbani; Mazumdar, Anwesh; Antia, H. M.; Demarque,
   Pierre
Bibcode: 2004MNRAS.350..277B
Altcode: 2004astro.ph..2360B
  Intermediate degree modes of the solar oscillations have previously
  been used to determine the solar helium abundance to a high degree of
  precision. However, we cannot expect to observe such modes in other
  stars. In this work we investigate whether low degree modes that
  should be available from space-based asteroseismology missions can
  be used to determine the helium abundance, Y, in stellar envelopes
  with sufficient precision. We find that the oscillatory signal in the
  frequencies caused by the depression in Γ<SUB>1</SUB> in the second
  helium ionization zone can be used to determine the envelope helium
  abundance of low-mass main-sequence stars. For frequency errors of one
  part in 10<SUP>4</SUP>, we expect errors σ<SUB>Y</SUB> in the estimated
  helium abundance to range from 0.03 for 0.8-M<SUB>solar</SUB> stars to
  0.01 for 1.2-M<SUB>solar</SUB> stars. The task is more complicated in
  evolved stars, such as subgiants, but is still feasible if the relative
  errors in the frequencies are less than 10<SUP>-4</SUP>.

Title: A Preliminary Seismic Analysis of 51 Pegasi: Large and Small
    Spacings from Standard Models
Authors: Murphy, Eric J.; Demarque, Pierre; Guenther, D. B.
Bibcode: 2004ApJ...605..472M
Altcode: 2003astro.ph.12554M
  We present a preliminary theoretical seismic study of the astronomically
  famous star 51 Peg. This is done by first performing a detailed analysis
  within the Hertzsprung-Russell diagram (HRD). Using the Yale stellar
  evolution code (YREC), a grid of stellar evolutionary tracks has been
  constructed for the masses 1.00, 1.05, and 1.10 M<SUB>solar</SUB>, in
  the metallicity range Z=0.024-0.044, and for values of the Galactic
  helium enrichment ratio (ΔY/ΔZ) in the range 0-2.5. Along these
  evolutionary tracks, we select 75 stellar model candidates that fall
  within the 51 Peg observational error box in the HRD (all turn out
  to have masses of 1.05 and 1.10M<SUB>solar</SUB>). The corresponding
  allowable age range for these models, which depends sensitively on the
  parameters of the model, is relatively large, ~2.5-5.5 Gyr. For each of
  the 75 models, a nonradial pulsation analysis is carried out and the
  large- and small-frequency spacings are calculated. The results show
  that just measuring the large- and small-frequency spacings will greatly
  reduce the present uncertainties in the derived physical parameters
  and in the age of 51 Peg. Finally, we briefly discuss refinements in
  the physics of the models and in the method of analysis, which will
  have to be included in future models to make the best of the precise
  frequency determinations expected from space observations.

Title: Three-dimensional simulations of the upper radiation-convection
    transition layer in subgiant stars
Authors: Robinson, F. J.; Demarque, P.; Li, L. H.; Sofia, S.; Kim,
   Y. -C.; Chan, K. L.; Guenther, D. B.
Bibcode: 2004MNRAS.347.1208R
Altcode:
  This paper describes three-dimensional (3D) large eddy simulations
  of stellar surface convection using realistic model physics. The
  simulations include the present Sun, a subgiant of one solar mass
  and a lower-gravity subgiant, also of one solar mass. We examine
  the thermal structure (superadiabaticity) after modification by 3D
  turbulence, the overshoot of convective motions into the radiative
  atmosphere and the range of convection cell sizes. Differences between
  models based on the mixing length theory (MLT) and the simulations
  are found to increase significantly in the more evolved stages as the
  surface gravity decreases. We find that the full width at half maximum
  (FWHM) of the turbulent vertical velocity correlation provides a good
  objective measure of the vertical size of the convective cells. Just
  below the convection surface, the FWHM is close to the mean vertical
  size of the granules and 2 × FWHM is close to the mean horizontal
  diameter of the granules. For the Sun, 2 × FWHM = 1200 km, a value
  close to the observed mean granule size. For all the simulations, the
  mean horizontal diameter is close to 10 times the pressure scaleheight
  at the photospheric surface, in agreement with previous work.

Title: Determining the helium abundance of stellar envelopes
Authors: Basu, S.; Antia, H. M.; Demarque, P.
Bibcode: 2004ESASP.538..273B
Altcode: 2004sshp.conf..273B
  Intermediate-degree mode solar oscillation have been used to determine
  the solar helium abundance to a high degree of precision. However, we
  cannot expect to observe these modes in other stars. We investigate
  whether low degree modes that should be available from space-based
  asteroseismology missions can be used to determine the helium abundance
  with sufficient precision. We find that the oscillatory signal in the
  frequencies caused by the depression in Γ<SUB>1</SUB> in the second
  helium ionisation zone can be used to determine the envelope helium
  abundance of low mass stars.

Title: The Production of Elements in Low-Mass Stars
Authors: Demarque, Pierre
Bibcode: 2003APS..DNP4WB002D
Altcode:
  A major source of many of the light elements, including carbon and
  nitrogen, as well as many of the s-process elements, is low-mass
  stars. In this context, not only are nuclear rates important, but so
  to is the astrophysics of convective dredge-up and rotation. In this
  talk, I will review the major processes that result in the ejection
  from low-mass stars of an important complement of the elements of
  the universe.

Title: Global Parameter and Helioseismic Tests of Solar Variability
    Models
Authors: Li, L. H.; Basu, S.; Sofia, S.; Robinson, F. J.; Demarque,
   P.; Guenther, D. B.
Bibcode: 2003ApJ...591.1267L
Altcode:
  We construct models of the structure and evolution of the Sun which
  include variable magnetic fields and turbulence. The magnetic
  effects are (1) magnetic pressure, (2) magnetic energy, and (3)
  magnetic modulation to turbulence. The effects of turbulence are (1)
  turbulent pressure, (2) turbulent kinetic energy, and (3) turbulent
  inhibition of the radiative energy loss of a convective eddy, and
  (4) turbulent generation of magnetic fields. Using these ingredients
  we construct five types of solar variability models (including the
  standard solar model) with magnetic effects. These models are in part
  based on three-dimensional numerical simulations of the superadiabatic
  layers near the surface of the Sun. The models are tested with several
  sets of observational data, namely, the changes of (1) the total solar
  irradiance, (2) the photospheric temperature, (3) radius, (4) the
  position of the convection zone base, and (5) low- and medium-degree
  solar oscillation frequencies. We find that turbulence plays a major
  role in solar variability, and only a model that includes a magnetically
  modulated turbulent mechanism can agree with all the current available
  observational data. We find that because of the somewhat poor quality
  of all observations (other than the helioseismological ones), we need
  all data sets in order to restrict the range of models.

Title: WOCS: Astrometry and Membership to V=21 in NGC 188
Authors: Platais, I.; Kozhurina-Platais, V.; Mathieu, R. D.; Demarque,
   P.; Girard, T. M.; van Altena, W. F.
Bibcode: 2003AAS...202.2705P
Altcode: 2003BAAS...35..734P
  The old open cluster NGC 188 is a cornerstone cluster for the WIYN
  Open Cluster Study (WOCS). In 2000 we presented first results of deep
  BV photometry and proper motions of NGC 188. In the meantime, the
  astrometric properties of the NOAO CCD Mosaic Imager have become better
  understood. Also, to the existing measurements of KPNO 4-m telescope
  plates we have added Mt. Wilson 60-in and Palomar 5-m telescope plates
  taken in the nineteen fifties. As a result, the precision of proper
  motions has improved by a factor of three, reaching 0.15 mas/yr for
  the best measured stars. These high-quality proper motions allow us to
  separate field stars from the cluster members with confidence. Some
  1,100 bona fide cluster members are found over the one-degree area
  down to V=21. We discuss essential properties of NGC 188 in light of
  the new astrometry, photometry and radial velocities. <P />This study
  is supported by NSF grant AST-0196075 to The Johns Hopkins University
  and NSF grant AST-9731302 to the University of Wisconsin - Madison

Title: Convection cells in a red giant atmosphere from 3D numerical
    simulations
Authors: Demarque, P.; Robinson, F. J.; Sofia, S.; Kim, Y. -C.; Chan,
   K. L.; Guenther, D. B.
Bibcode: 2003AAS...202.3208D
Altcode: 2003BAAS...35..744D
  Results of a 3D radiative hydrodynamical simulation of atmospheric
  convection, applicable to a red giant star of one solar mass with
  log g = 2.6, are presented, with special emphasis on the scale of the
  convective cells. Since the work of Schwarzschild (1975), it has been
  expected, by analogy with the Sun, that convective cell size scales
  with the atmospheric scale height H<SUB>p</SUB> and the width of the
  highly superadiabatic transition layer (SAL). Based on his estimate
  of the SAL, Schwarzschild (1975) predicted a few hundred cells on
  a giant and fewer (possibly even just a few) cells on a supergiant
  like Betelgeuse, in contrast with the two million cells observed on
  the solar surface. Freytag et al (1999)'s 10H<SUB>p</SUB> scaling
  law, based on 2D numerical simulations, suggests a few hundred cells
  on a supergiant. <P />This work is an extension to a lower surface
  gravity of earlier 3D simulations for the Sun (Robinson et al. 2003a)
  and subgiant stars (Robinson et al. 2003b). Preliminary extrapolation
  from these simulations predicts that the surface of a giant with log
  g = 2.6 has approximately 40,000 cells. Betelgeuse, with log g = -0.5,
  would have approximately 300 cells. This number of cells is compatible
  with Gray's (2001) spectroscopic observations of Betelgeuse, although
  other observations of its surface brightness have been interpreted
  as due to fewer giant cells. <P />The convection scale size from
  the giant simulation is compared to previous extrapolations and to
  observation. <P />This work was supported in part by research grants
  from NASA (NAG5-8406), Yonsei University and NSERC of Canada.

Title: Three-dimensional convection simulations of the outer layers
    of the Sun using realistic physics
Authors: Robinson, F. J.; Demarque, P.; Li, L. H.; Sofia, S.; Kim,
   Y. -C.; Chan, K. L.; Guenther, D. B.
Bibcode: 2003MNRAS.340..923R
Altcode: 2002astro.ph.12296R
  This paper describes a series of three-dimensional simulations of
  shallow inefficient convection in the outer layers of the Sun. The
  computational domain is a closed box containing the convection-radiation
  transition layer, located at the top of the solar convection zone. The
  most salient features of the simulations are that: (i) the position
  of the lower boundary can have a major effect on the characteristics
  of solar surface convection (thermal structure, kinetic energy and
  turbulent pressure); (ii) the width of the box has only a minor
  effect on the thermal structure, but a more significant effect on
  the dynamics (rms velocities); (iii) between the surface and a depth
  of 1 Mm, even though the density and pressure increase by an order
  of magnitude, the vertical correlation length of vertical velocity
  is always close to 600 km; (iv) in this region the vertical velocity
  cannot be scaled by the pressure or the density scaleheight; this casts
  doubt on the applicability of the mixing length theory, not only in
  the superadiabatic layer, but also in the adjacent underlying layers;
  (v) the final statistically steady state is not strictly dependent on
  the initial atmospheric stratification.

Title: Helioseismic tests of solar variability models
Authors: Li, L. H.; Basu, S.; Sofia, S.; Robinson, F. J.; Demarque,
   P.; Guenther, D. B.
Bibcode: 2003ESASP.517..329L
Altcode: 2003soho...12..329L
  We construct models of the structure and evolution of the Sun which
  includes variable magnetic fields and turbulence. The magnetic effects
  included are: (1) magnetic pressure, (2) magnetic energy, and (3)
  magnetic modulation of turbulence. The effects of turbulence are:
  (1) turbulent pressure, (2) turbulent kinetic energy, (3) inhibition
  of radiative losses from a convective eddy, and (4) generation of
  magnetic fields. Using these ingredients we construct various types
  of solar models and test them against helioseismic data. We find that
  only a solar variability model which includes a magnetically-modulated
  mechanism to generate turbulence can agree with all the current
  available observational data.

Title: The Y<SUP>2</SUP> Stellar Evolutionary Tracks
Authors: Yi, Sukyoung K.; Kim, Yong-Cheol; Demarque, Pierre
Bibcode: 2003ApJS..144..259Y
Altcode: 2002astro.ph.10201Y
  We present a database of the latest stellar models of the Y<SUP>2</SUP>
  (Yonsei-Yale) collaboration. This database contains the stellar
  evolutionary tracks from the pre-main-sequence birthline to the
  helium core flash that were used to construct the Y<SUP>2</SUP>
  isochrones. We also provide a simple interpolation routine that
  generates stellar tracks for given sets of parameters (metallicity,
  mass, and α-enhancement).

Title: Testing Intermediate-Age Stellar Evolution Models with VLT
    Photometry of Large Magellanic Cloud Clusters. I. The Data
Authors: Gallart, Carme; Zoccali, Manuela; Bertelli, Gianpaolo;
   Chiosi, Cesare; Demarque, Pierre; Girardi, Leo; Nasi, Emma; Woo,
   Jong-Hak; Yi, Sukyoung
Bibcode: 2003AJ....125..742G
Altcode: 2002astro.ph..8188G
  This is the first of a series of three papers devoted to the calibration
  of a few parameters of crucial importance in the modeling of the
  evolution of intermediate-mass stars, giving special attention to the
  amount of convective core overshoot. To this end we acquired deep V
  and R photometry for three globular clusters of the Large Magellanic
  Cloud, namely, NGC 2173, SL 556, and NGC 2155, in the age interval 1-3
  Gyr. In this first paper, we describe the aim of the project and Very
  Large Telescope observations and data reduction and we make preliminary
  comparisons of the color-magnitude diagrams with both the Padova and
  Yonsei-Yale isochrones. Two following papers in this series present the
  results of a detailed analysis of these data, independently carried
  out by members of the Yale and Padova stellar evolution groups. This
  allows us to compare both sets of models and discuss their main
  differences, as well as the systematic effects that they would have on
  the determination of the ages and metallicities of intermediate-age
  single-stellar populations. <P />Based on observations collected at
  the European Southern Observatory, Paranal, Chile (ESO 64.L-0385).

Title: Testing Intermediate-Age Stellar Evolution Models with VLT
    Photometry of Large Magellanic Cloud Clusters. II. Analysis with
    the Yale Models
Authors: Woo, Jong-Hak; Gallart, Carme; Demarque, Pierre; Yi, Sukyoung;
   Zoccali, Manuela
Bibcode: 2003AJ....125..754W
Altcode: 2002astro.ph..8142W
  Using Yale stellar evolution models, we present an analysis of the
  color-magnitude diagrams (CMDs) of three intermediate-age LMC clusters,
  namely, NGC 2173, SL 556, and NGC 2155, obtained with the Very Large
  Telescope. The main goal of our project is to investigate the amount of
  convective core overshoot necessary to reproduce the CMDs of relatively
  metal-poor, intermediate-age stellar populations, to check whether the
  extrapolation that is usually made from solar metallicity is valid. In
  the process, we obtained values for the binary fraction of each cluster,
  together with refined age estimates. Our method involved the comparison
  of the observed CMDs with synthetic CMDs computed using various values
  of the overshoot parameter and binary fraction. We conclude that a
  moderate amount of overshoot and some fraction of binary stars are
  essential for reproducing the observed shapes around the turnoff in
  the CMDs of all three clusters: unresolved binary stars fill in the
  expected core contraction gap and make a unique sequence near the
  gap, which cannot be reproduced by single stars alone, even with a
  larger amount of overshoot. We utilize ratios of the number of stars
  in different areas around the core contraction gap to constrain the
  binary fraction, which is around 10%-20% (for primary-to-secondary mass
  ratio &gt;=0.7) in all three clusters. Even if binary stars contaminate
  the core contraction gap, it is shown that the overshoot parameter
  can be inferred from the color dispersion of the stars around the
  contraction gap, regardless of the assumed binary fraction. From
  our overall analysis such as shape of isochrones, star counts,
  color distribution, and synthetic CMD comparisons, we conclude that
  overshoot ~20% of the local pressure scale height best reproduces the
  CMD properties of all three clusters. The best age estimates are 1.5,
  2.1, and 2.9 Gyr for NGC 2173, SL 556, and NGC 2155, respectively. <P
  />Based on observations collected at the European Southern Observatory,
  Paranal, Chile (ESO 64.L-0385).

Title: The Y<SUP>2</SUP> Isochrones
Authors: Yi, S.; Demarque, P.; Kim, Y. C.
Bibcode: 2003ASPC..296..240Y
Altcode: 2003nhgc.conf..240Y
  No abstract at ADS

Title: The Y <SUP>2</SUP> Isochrones and Stellar Evolution Tracks
Authors: Yi, Sukyoung K.; Demarque, Pierre; Kim, Yong-Cheol
Bibcode: 2003egcs.conf..255Y
Altcode:
  We present a new set of isochrones in which the effect of the α-element
  enhancement is fully incorporated. The isochrone tables, together with
  interpolation routines in age and chemical composition, and in [α/Fe]
  are available on request as well as from the electronic version of
  our ApJ papers. Newly-derived ages of Galactic globular clusters using
  these isochrones are 20 to 30% smaller than previous estimates. This
  is a summary of our upcoming papers (Kim et al. 2002; Yi et al. 2003).

Title: Radiative Hydrodynamical Simulations of Granulation in the
    Sun at Different Stages Along the Evolutionary Track
Authors: Robinson, F. J.; Demarque, P.; Li, L. H.; Sofia, S.; Kim,
   Y. -C.; Guenther, D. B.
Bibcode: 2003ASPC..293..221R
Altcode: 2003tdse.conf..221R
  Realistic solar surface simulations in 3 dimensions have been primarily
  done for the Sun. This is a logical first step as there is much more
  accurate observational data available for the Sun than for any other
  star. After reproducing observed characteristics of solar surface
  convection, we apply our 3D model to the Sun at later evolutionary
  stages. We find that while the superadiabatic layer (SAL) in the
  subgiant is similar to the Sun, the red giant has a much broader and
  lower SAL. The maximum turbulent pressure and maximum turbulent kinetic
  energy in the giant are almost double that of the other models. The
  asymmetry between upflow and downflow seems to decrease as the Sun
  evolves. This will reduce the size of the kinetic energy flux. We find
  a linear relationship between the depth of the granules and the surface
  gravity of the model. Extrapolating to log g = -0.5 (estimated surface
  gravity of Betelgeuse) suggests about 1000 granules would be required
  to cover the entire surface of Betelgeuse.

Title: Three-Dimensional Radiative Hydrodynamical Simulations of
    the Outer Layers of Sun-Like Stars
Authors: Demarque, P.; Li, L. H.; Robinson, F. J.; Sofia, S.; Guenther,
   D. B.
Bibcode: 2003aahd.conf..509D
Altcode:
  No abstract at ADS

Title: Stellar Convection
Authors: Demarque, Pierre; Robinson, Francis J.
Bibcode: 2003Ap&SS.284..193D
Altcode:
  Seismology provides powerful tests of convection deep in stellar
  interiors. First, the role of convective overshoot and low efficiency
  convection, two areas of uncertainty with important astrophysical
  implications, are reviewed briefly. In the rest of the talk, a critical
  introduction to numerical simulations of radiative hydrodynamics will
  be given. The basic underlying assumptions and challenges are explained,
  and some recent results are presented.

Title: Effects of Domain Size on Surface Simulations of the Sun
Authors: Robinson, F. J.; Li, L. H.; Demarque, P.; Sofia, S.; Kim,
   Y. -C.; Guenther, D. B.
Bibcode: 2003IAUS..210P..C3R
Altcode:
  No abstract at ADS

Title: The Scale of Granulation in Red Giant Atmospheres
Authors: Demarque, P.; Robinson, F. J.; Chan, K. L.; Kim, Y. -C.;
   Guenther, D. B.; Sofia, S.
Bibcode: 2002AAS...20111506D
Altcode: 2002BAAS...34Q1291D
  The scale of photospheric convection in red giants is generally
  associated, by analogy with the Sun, with the atmospheric pressure scale
  height and the thickness of the superadiabatic transition layer. As
  pointed out by Schwarzschild (1975), both of these quantities are
  relatively much larger in terms of the stellar radius in a red giant
  than in the Sun. On these grounds, Schwarzschild concluded that only
  a few cells must be present on a red giant surface, in contrast with
  two millions cells observed on the solar surface. Observations of
  brightness variations in the TiO band on Betelgeuse (Gaustad 1986) and
  direct imaging of Betelgeuse (Gilliland &amp; Dupree 1996) with HST
  have yielded results that are compatible with giant cells, although
  other interpretations (e.g. pulsation) are possible. 2D numerical
  simulations (Freytag et al. 2001) also claim compatibility with the
  giant cell interpretation. On the other hand, Gray (2001) has pointed
  out that his extensive spectroscopic observations of Betelgeuse are more
  easily interpreted in terms of many convection cells per hemisphere. We
  present preliminary results of 3D radiative hydrodynamical simulations
  which corroborate Gray's interpretation. This work is supported in
  part by NASA grant NAG5-8406

Title: The Y<SUP>2</SUP> Isochrones for α-Element Enhanced Mixtures
Authors: Kim, Yong-Cheol; Demarque, Pierre; Yi, Sukyoung K.; Alexander,
   David R.
Bibcode: 2002ApJS..143..499K
Altcode: 2002astro.ph..8175.; 2002astro.ph..8175C; 2002astro.ph..8175K
  We present a new set of isochrones in which the effect of the
  α-element enhancement is fully incorporated. These isochrones are an
  extension of the already published set of Y<SUP>2</SUP> Isochrones
  (our Paper I), constructed for the scaled-solar mixture. As in
  Paper I, helium diffusion and convective core overshoot have been
  taken into account. The range of chemical compositions covered
  is 0.00001&lt;=Z&lt;=0.08. The models were evolved from the
  pre-main-sequence stellar birthline to the onset of helium burning
  in the core. The age range of the full isochrone set is 0.1-20 Gyr,
  while younger isochrones of age 1-80 Myr are also presented up to
  the main-sequence turn-off. Combining this set with that of Paper I
  for scaled-solar mixture isochrones, we provide a consistent set of
  isochrones that can be used to investigate populations of any value of
  α-enhancement. We confirm the earlier results of Paper I that inclusion
  of α-enhancement effects further reduces the age estimates of globular
  clusters by approximately 8% if [α/Fe]=+0.3. It is important to note
  the metallicity dependence of the change in age estimates (larger age
  reductions in lower metallicities). This reduces the age gap between
  the oldest metal-rich and metal-poor Galactic stellar populations and
  between the halo and the disk populations. We also investigate whether
  the effects of α-enhancement can be mimicked by increasing the total
  metal abundance in the manner proposed by Salaris and collaborators. We
  find such simple scaling formulae are valid at low metallicities but
  not at all at high metallicities near and above solar. Thus, it is
  essential to use the isochrones rigorously computed for α-enhancement
  when modeling metal-rich populations, such as bright galaxies. The
  isochrone tables, together with interpolation routines have been made
  available via internet.

Title: Seismic Test of Solar Models, Solar Neutrinos, and Implications
    for Metal-rich Accretion
Authors: Winnick, R. A.; Demarque, Pierre; Basu, Sarbani; Guenther,
   D. B.
Bibcode: 2002ApJ...576.1075W
Altcode: 2001astro.ph.11096W
  The Sun is believed to have been the recipient of a substantial amount
  of metal-rich material over the course of its evolution, particularly
  in the early stages of the solar system. With a long diffusion
  timescale, the majority of this accreted matter should still exist in
  the solar convection zone, enhancing its observed surface abundance,
  and implying a lower abundance core. While helioseismology rules out
  solar models with near-zero metallicity cores, some solar models with
  enhanced metallicity in the convection zone might be viable, as small
  perturbations to the standard model. Because of the reduced interior
  opacity and core temperature, the neutrino flux predicted for such
  models is lower than that predicted by the standard solar model. This
  paper examines how compatible inhomogeneous solar models of this kind
  are with the observed low and intermediate degree p-mode oscillation
  data, and with the solar neutrino data from the Sudbury Neutrino
  Observatory Collaboration. We set an upper limit on how much metal-rich
  accretion took place during the early evolution of the Sun at ~2
  M<SUB>⊕</SUB> of iron (or ~40 M<SUB>⊕</SUB> of meteoric material).

Title: High-Amplitude δ Scuti and SX Phoenicis Stars: The Effects of
    Chemical Composition on Pulsations and the Period-Luminosity Relation
Authors: Templeton, Matthew; Basu, Sarbani; Demarque, Pierre
Bibcode: 2002ApJ...576..963T
Altcode:
  We present a theoretical study of the radially pulsating δ Scuti
  and SX Phoenicis variables, concentrating on the blue straggler SX
  Phoenicis variables found in globular clusters. We have evolved a grid
  of stellar models with the metal abundance of the globular cluster M55,
  including models with alpha-enhanced metal abundances, and tested these
  models for radial pulsations observed in the high-amplitude δ Scuti
  and SX Phoenicis stars. Our grid includes models with globally enriched
  helium content to simulate the effects of stellar collisions and global
  mixing possible in blue stragglers. We find that global enrichment of
  helium strongly affects the temperature and luminosity of a given star,
  but the location of the instability strip blue edge and the slope of
  the period-luminosity (PL) relation are unchanged. This suggests that
  the PL relation is not affected by blue straggler formation if blue
  stragglers are fully mixed stellar mergers. Our blue edges and PL
  relations are in agreement with other theoretical determinations and
  also with the observational PL relation of M55, but they are not in
  agreement with the PL relation previously derived for high-amplitude
  δ Scuti stars in the field. Analysis of the double-mode variable,
  V41, suggests either that the star may not be pulsating in the first
  and second overtones as claimed or that normal stellar models may not
  be accurate models of blue straggler stars.

Title: Helioseismic tests of a new category of solar models
Authors: Li, L. H.; Basu, Sarbani; Sofia, S.; Demarque, Pierre
Bibcode: 2002ESASP.508...83L
Altcode: 2002soho...11...83L
  We have constructed a series of solar models that unlike others which
  treat the effects of magnetic fields as a perturbation, incorporate the
  effect of magnetic fields into the stellar structure equations. Such
  models can reproduce the observed irradiance and effective temperature
  variations of the Sun. We study the helioseismic properties of
  these models representing different epochs of the solar cycle. In
  particular we examine whether the frequency differences between the
  models reproduce the observed solar-cycle related change of solar
  oscillation frequencies.

Title: Inclusion of Turbulence in Solar Modeling
Authors: Li, L. H.; Robinson, F. J.; Demarque, P.; Sofia, S.; Guenther,
   D. B.
Bibcode: 2002ApJ...567.1192L
Altcode: 2001astro.ph..9078L
  The general consensus is that in order to reproduce the observed solar
  p-mode oscillation frequencies, turbulence should be included in solar
  models. However, until now there has not been any well-tested efficient
  method to incorporate turbulence into solar modeling. We present here
  two methods to include turbulence in solar modeling within the framework
  of the mixing length theory, using the turbulent velocity obtained
  from numerical simulations of the highly superadiabatic layer (SAL)
  of the Sun at three stages of its evolution. The first approach is to
  include the turbulent pressure alone, and the second is to include
  both the turbulent pressure and the turbulent kinetic energy. The
  latter is achieved by introducing two variables: the turbulent kinetic
  energy per unit mass and the effective ratio of specific heats owing
  to the turbulent perturbation. These are treated as additions to the
  standard thermodynamic coordinates (e.g., pressure and temperature). We
  investigate the effects of both treatments of turbulence on the
  structure variables, the adiabatic sound speed, the structure of
  the highly superadiabatic layer, and the p-mode frequencies. We
  find that the second method reproduces the SAL structure obtained in
  three-dimensional simulations and produces a p-mode frequency correction
  an order of magnitude better than the first method.

Title: Testing Overshoot with Intermediate-age Magellanic Cloud
    Clusters
Authors: Woo, J. -H.; Gallart, C.; Demarque, P.; Yi, S.; Zoccali, M.
Bibcode: 2002ASPC..274..377W
Altcode: 2002ohds.conf..377W
  No abstract at ADS

Title: Modification of the Core Overshoot Treatment
Authors: Woo, Jong-Hak; Demarque, Pierre; Yi, Sukyoung
Bibcode: 2002IAUS..207..736W
Altcode:
  Following Roxburgh's integral constraint, we implemented an upper
  limit of overshoot in the conventional method of α parameterization
  in order to remove an overly large overshoot effect for low-mass
  stars. The erroneously large effect of overshoot due to the failure
  of α parameterization can be effectively corrected by limiting the
  amount of overshoot to 15 % of the core radius.

Title: The Y<SUP>2</SUP> Isochrones
Authors: Yi, S. K.; Demarque, P.; Kim, Y. -C.; Lee, Y. -W.; Ree,
   C. H.; Lejeune, T.
Bibcode: 2002ASPC..274...45Y
Altcode: 2002ohds.conf...45Y
  No abstract at ADS

Title: Testing Intermediate-age Stellar Evolution with Magellanic
    Cloud Clusters
Authors: Gallart, Carme; Zoccali, Manuela; Bertelli, Giampaolo;
   Chiosi, Cesare; Demarque, Pierre; Girardi, Leo; Yi, Sukyoung
Bibcode: 2002IAUS..207..713G
Altcode:
  We present new deep VLT color-magnitude diagrams of three
  intermediate-age populous star clusters in the LMC. These data will
  be used independently by the Padova and Yale stellar evolution Groups
  to address issues relevant to the evolution of intermediate-mass
  stars: mainly the extent of the core convective overshoot, as well as
  other poorly determined parameters, such as mass loss during stellar
  evolution, internal rotation, and He content.

Title: VizieR Online Data Catalog: NGC 2451A proper motions and
    membership (Platais+, 2001)
Authors: Platais, I.; Kozhurina-Platais, V.; Barnes, S.; Girard,
   T. M.; Demarque, P.; van Altena, W. F.; Deliyannis, C. P.; Horch, E.
Bibcode: 2002yCat..51221486P
Altcode:
  We provide new evidence that NGC 2451A is undoubtedly a young open
  cluster, although sparsely populated. New cluster membership has been
  derived from relative proper motions of 5868 stars. In total, 136
  stars down to V~15 5 have membership probability Pμ&gt;=2%. New CCD
  BV photometry indicates that about 70 stars are indeed main-sequence
  stars of NGC 2451A. This is also supported by our measurements
  of radial velocities. A total of 34 very likely cluster members
  yield a mean heliocentric radial velocity for NGC 2451A equal to
  +22.9km/s. The high quality of our BV photometry, a confirmation of
  cluster membership from proper motions and radial velocities, and
  a recently obtained metallicity estimate for several cluster stars
  allow us to perform a precise isochrone fit. The Yale isochrones,
  updated by the latest available input physics, have been fitted to
  the cluster's color-magnitude diagram, yielding a distance modulus
  V<SUB>0</SUB>-M<SUB>V</SUB> in the range 6.35 to 6.38, which is in
  excellent agreement with the distance modulus (m-M)<SUB>0</SUB>=6.38
  derived from the Hipparcos data recently by van Leeuwen and
  Robichon et al. (1998, Cat. &lt;J/A+AS/130/157&gt;). We have used
  the high-resolution spectra acquired using the Hydra multiobject
  spectrograph at the WIYN telescope (Kitt Peak, Arizona) in 1997 November
  and 1998 October. <P />(4 data files).

Title: Towards Better Age Estimates for Stellar Populations: The
    Y<SUP>2</SUP> Isochrones
Authors: Demarque, Pierre; Yi, Sukyoung; Kim, Yong-Cheol
Bibcode: 2002IAUS..207..711D
Altcode:
  New theoretical isochrones are presented and compared to the
  observational data.

Title: Asteroseismology of Delta Scuti Stars - A Parameter Study
Authors: Templeton, M.; Basu, S.; Demarque, P.
Bibcode: 2002ASPC..259..600T
Altcode: 2002rnpp.conf..600T; 2002IAUCo.185..600T
  No abstract at ADS

Title: Update on globular cluster ages
Authors: Demarque, Pierre; Kim, Young-Cheo; Yi, Sukyoung
Bibcode: 2002ASSL..274..111D
Altcode:
  We update globular cluster age estimates and discuss their implications
  in the context of present knowledge in cosmology. On the basis of
  the best information now available, the ages of the oldest globular
  clusters are estimated at 13.0±1.5 Gyr. If this result, whose main
  uncertainty is primarily in the distance scale, continues to hold,
  the long standing discrepancy between the stellar evolution timescale
  and the universal expansion timescale will have been resolved.

Title: Asteroseismology of δ Scuti Stars: A Parameter Study and
    Application to Seismology of FG Virginis
Authors: Templeton, Matthew; Basu, Sarbani; Demarque, Pierre
Bibcode: 2001ApJ...563..999T
Altcode: 2001astro.ph..8458T
  We assess the potential of asteroseismology for determining the
  fundamental properties of individual δ Scuti stars. We computed a grid
  of evolution and adiabatic pulsation models using the Yale Rotating
  Evolution Code to study the systematic changes in low-order (l=0, 1, 2,
  and 3) modes as functions of fundamental stellar properties. Changes to
  the stellar mass, chemical composition, and convective core overshooting
  length change the observable pulsation spectrum significantly. In
  general, mass has the strongest effect on evolution and on pulsation
  followed by the metal abundance. Changes to the helium content have
  very little effect on the frequencies until near the end of the main
  sequence. Changes to each of the four parameters change the p-mode
  frequencies more, in both absolute and relative terms, than they do
  the g- and mixed-mode frequencies, suggesting that these parameters
  have a greater effect on the outer layers of the star. We also
  present evolution and pulsation models of the well-studied star FG
  Virginis, outlining a possible method of locating favorable models
  in the stellar parameter space based on a definitive identification
  of only two modes. Specifically, we plot evolution models on the
  (period-period ratio) and (temperature-period ratio) planes to select
  candidate models and modify the core overshooting parameter to fit the
  observed star. For these tests, we adjusted only the mass, helium and
  metal abundances, and core overshooting parameter, but this method can
  be extended to include the effects of first-order rotational splitting
  and second-order rotational distortion of pulsation spectra.

Title: Toward Better Age Estimates for Stellar Populations: The
    Y<SUP>2</SUP> Isochrones for Solar Mixture
Authors: Yi, Sukyoung; Demarque, Pierre; Kim, Yong-Cheol; Lee,
   Young-Wook; Ree, Chang H.; Lejeune, Thibault; Barnes, Sydney
Bibcode: 2001ApJS..136..417Y
Altcode: 2001astro.ph..4292Y
  We have constructed a new set of isochrones, called the Y<SUP>2</SUP>
  Isochrones, that represent an update of the Revised Yale Isochrones
  (RYI), using improved opacities and equations of state. Helium
  diffusion and convective core overshoot have also been taken into
  consideration. This first set of isochrones is for the scaled solar
  mixture. A subsequent paper will consider the effects of α-element
  enhancement, believed to be relevant in many stellar systems. Two
  additionally significant features of these isochrones are that (1)
  the stellar models start their evolution from the pre-main-sequence
  birthline instead of from the zero-age main sequence and (2)
  the color transformation has been performed using both the latest
  table of Lejeune et al., and the older, but now modified, Green et
  al. table. The isochrones have performed well under the tests conducted
  thus far. The reduction in the age of the Galactic globular clusters
  caused by this update in stellar models alone is approximately 15%
  relative to RYI-based studies. When the suggested modification for the
  α-element enhancement is made as well, the total age reduction becomes
  approximately 20%. When post-RGB evolutionary stages are included,
  we find that the ages of globular clusters derived from integrated
  colors are consistent with the isochrone fitting ages.

Title: Empirical Constraints on Convective Core Overshoot
Authors: Woo, Jong-Hak; Demarque, Pierre
Bibcode: 2001AJ....122.1602W
Altcode: 2001astro.ph..6061W
  In stellar evolution calculations, the local pressure scale height
  is often used to empirically constrain the amount of convective core
  overshoot. However, this method brings unsatisfactory results for
  low-mass stars (&lt;=1.1-1.2 M<SUB>solar</SUB> for Z=Z<SUB>solar</SUB>),
  which have very small cores or no convective core at all. Following
  Roxburgh's integral constraint, we implemented an upper limit of
  overshoot within the conventional method of α parameterization
  to remove an overly large overshoot effect on low-mass stars. The
  erroneously large effect of core overshoot due to the failure of α
  parameterization can be effectively corrected by limiting the amount of
  overshoot to &lt;=15% of the core radius; 15% of the core radius would
  be a proper limit of overshoot, which can be implemented in a stellar
  evolution code for intermediate- to low-mass stars. The temperature
  structure of the overshoot region does not play a crucial role in
  stellar evolution since this transition region is very thin.

Title: WIYN Open Cluster Study. VII. NGC 2451A and the Hipparcos
    Distance Scale
Authors: Platais, Imants; Kozhurina-Platais, Vera; Barnes, Sydney;
   Girard, Terrence M.; Demarque, Pierre; van Altena, William F.;
   Deliyannis, Constantine P.; Horch, Elliott
Bibcode: 2001AJ....122.1486P
Altcode:
  We provide new evidence that NGC 2451A is undoubtedly a young open
  cluster, although sparsely populated. New cluster membership has been
  derived from relative proper motions of 5868 stars. In total, 136 stars
  down to V~15 have membership probability P<SUB>μ</SUB>&gt;=2%. New CCD
  BV photometry indicates that about 70 stars are indeed main-sequence
  stars of NGC 2451A. This is also supported by our measurements of
  radial velocities. A total of 34 very likely cluster members yield
  a mean heliocentric radial velocity for NGC 2451A equal to +22.9 km
  s<SUP>-1</SUP>. The high quality of our BV photometry, a confirmation
  of cluster membership from proper motions and radial velocities, and
  a recently obtained metallicity estimate for several cluster stars
  allow us to perform a precise isochrone fit. The Yale isochrones,
  updated by the latest available input physics, have been fitted to
  the cluster's color-magnitude diagram, yielding a distance modulus
  V<SUB>0</SUB>-M<SUB>V</SUB> in the range 6.35 to 6.38, which is in
  excellent agreement with the distance modulus (m-M)<SUB>0</SUB>=6.38
  derived from the Hipparcos data recently by van Leeuwen and Robichon
  et al. For NGC 2451A the isochrone fit yields an age of 60+/-20 Myr;
  hence, the cluster appears to be somewhat younger than the Pleiades. We
  also present alternative evidence suggesting that the cluster could
  be slightly older than the Pleiades. The most important result of
  this study is an excellent match between the main-sequence fitting and
  Hipparcos distances to NGC 2451A. If we consider noticeable similarities
  between NGC 2451A and Pleiades, then the Hipparcos distance anomaly
  for Pleiades may not require an explanation of astrophysical nature.

Title: Yonsei-Yale Isochrones: the status report
Authors: Kim, Y. -C.; Yi, S. K.; Demarque, P.
Bibcode: 2001AAS...198.4301K
Altcode: 2001BAAS...33..844K
  This poster is the first major progress report of the Yonsei-Yale
  Isochrone Project. The use of isochrones has grown steadily. The
  isochrone fitting technique has been a corner stone in the study
  of formation and evolution of the Milky Way. Thanks to the recent
  improvement in the input physics (opacities and EOS, etc.), we now boast
  of knowing the age of the Milky Way within 20% uncertainty. Recently,
  various population synthesis studies have shown that isochrones
  can be of great power in understanding the evolution of external
  galaxies as well, by matching their colors and spectra. Numerous
  studies demonstrated that isochrones can even help us to select a more
  likely cosmology model, not just the age of the universe. Those also
  showed only carefully constructed isochrones can provide the required
  accuracy. Therefore, there have been demands for an updated full-set
  of isochrones. The Yonsei-Yale Isochrone Project has been designed
  and carried out to fulfill such needs. This new isochrones would
  create particularly positive impacts to the astronomical community in
  general. In this poster, we report the availability of the Yonsei-Yale
  Isochrone standard set, and the current status of the project will
  be reported.

Title: Radiative hydrodynamics in the highly super adiabatic layer
    of stellar evolution models
Authors: Robinson, F. J.; Demarque, P.; Sofia, S.; Chan, K. L.; Kim,
   Y. -C.; Guenther, D. B.
Bibcode: 2001ESASP.464..443R
Altcode: 2000astro.ph.11065R; 2001soho...10..443R
  We present results of three dimensional simulations of the
  uppermost part of the sun, at 3 stages of its evolution. Each model
  includes physically realistic radiative-hydrodynamics (the Eddington
  approximation is used in the optically thin region), varying opacities
  and a realistic equation of state (full treatment of the ionization
  of H and He). In each evolution model, we investigate a domain,
  which starts at the top of the photosphere and ends just inside the
  convection zone (about 2400 km in the sun model). This includes all
  of the super-adiabatic layer (SAL). Due to the different positions
  of the three models in the log(g) vs logT<SUB>eff</SUB> plane, the
  more evolved models haved lower density atmospheres. The reduction
  in density causes the extent of overshoot into the radiation layer,
  to be greater in the more evolved models.

Title: The effect of turbulent pressure on the p-mode frequencies
    in stellar models
Authors: Demarque, P.; Li, L. H.; Robinson, F. J.; Sofia, S.; Kim,
   Y. -C.; Chan, K. L.; Guenther, D. B.
Bibcode: 2001ESASP.464..423D
Altcode: 2000astro.ph.11064D; 2001soho...10..423D
  We have constructed models for the sun at three stages of its evolution:
  a zero-age main sequence model, the present sun, and a subgiant
  model. For each model, the turbulent pressure and turbulent kinetic
  energy were calculated from 3-d radiative hydrodynamical simulations
  (described in the poster by Robinson et al.), and inserted into the
  1-d stellar models. We note that in these simulations, the turbulent
  pressure is not a free parameter, but can be computed from the resulting
  velocity field. We show the calculated p-mode frequencies for the model
  of the present sun, with and without turbulent pressure, and compare
  them to the observed solar frequencies. When the turbulent pressure is
  included in the models, the calculated frequencies are brought closer
  to the observed frequencies in the sun by up to two μHz, strictly
  from structural effects. The effect of including turbulent pressure
  on p-mode frequencies is also shown for the zero-age main sequence
  model. Our models also suggest that the importance of turbulent pressure
  increases as the star evolves into the subgiant region. We discuss the
  importance of also including realistic turbulence as well as radiation
  in the non-adiabatic calculation of oscillation frequencies.

Title: Convection, Angular Momentum Transfer and Mixing Mechanisms
in Late-Type Stars (CD-ROM Directory: contribs/demarque)
Authors: Demarque, P.
Bibcode: 2001ASPC..223..179D
Altcode: 2001csss...11..179D
  No abstract at ADS

Title: Hubble Space Telescope Photometry of the Metal-rich Globular
    Clusters NGC 6624 and NGC 6637
Authors: Heasley, J. N.; Janes, K. A.; Zinn, Robert; Demarque, Pierre;
   Da Costa, Gary S.; Christian, Carol A.
Bibcode: 2000AJ....120..879H
Altcode:
  We have observed the metal-rich globular clusters NGC 6624 and NGC
  6637 (M69) using the planetary camera of the WFPC2 on the Hubble Space
  Telescope (HST). Observations of the Ca II triplet lines in giant stars
  in these clusters show that NGC 6624 and NGC 6637 have metallicities
  on the Zinn and West scale of [Fe/H]=-0.63+/-0.09 and -0.65+/-0.09,
  only slightly more metal rich than 47 Tuc [Fe/H]=-0.71+/-0.07. For
  clusters of identical (or nearly so) metallicity, one can make a direct
  comparison of the color-magnitude diagrams to derive the relative ages
  of the clusters. From the color-magnitude diagrams derived from the HST
  photometry, we find that NGC 6624 and NGC 6637 differ in age by less
  than 0.5 Gyr. Their color-magnitude diagrams are also compared with
  those of 47 Tuc and NGC 6352, and while these latter diagrams are of
  somewhat lower quality, they are consistent with all of these clusters
  having the same ages. Adopting an apparent distance modulus of 13.40 and
  reddening E(B-V)=0.04 for 47 Tuc, the new Yale isochrones yield an age
  for the clusters of 14 Gyr. The positions of NGC 6624 and NGC 6637 in
  the Galaxy suggest that they belong to the bulge population of globular
  clusters. The only other bulge clusters that have been dated so far are
  the more metal rich clusters NGC 6528 and NGC 6553, which also appear
  to be very old. Consequently, the age-metallicity relation of the bulge
  may be very steep. The close similarity of the ages and metallicities
  of NGC 6624 and NGC 6637 to the thick-disk globular clusters 47 Tuc
  and NGC 6352 indicates that the age-metallicity relations of these
  populations intersect. We briefly discuss the possibility that these
  populations had a common origin. Based on observations made with the
  Anglo-Australian Telescope, Canada-France-Hawaii Telescope, and the
  NASA/ESA Hubble Space Telescope. The observations from the Hubble Space
  Telescope were obtained 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: Mass Loss on the Horizontal Branch: An Application to NGC 6791
Authors: Yong, Hwanjong; Demarque, Pierre; Yi, Sukyoung
Bibcode: 2000ApJ...539..928Y
Altcode: 2000astro.ph..3425Y
  The presence of a substantial number of hot stars in the extremely
  metal-rich open cluster NGC 6791 has been a mystery. If these hot stars
  are in their core helium-burning phase, they are significantly bluer
  (hotter) than predicted by canonical stellar evolution theory. No
  obvious explanation is available yet. We consider the effects of
  mass loss during the evolution of horizontal-branch (HB) stars as
  their possible origin. We find that the addition of mass loss causes
  HB stars to evolve to be hotter and fainter. Mass loss has a more
  pronounced effect for less massive stars and thus naturally widens the
  temperature (and color) distribution on the HB. If mass-loss rates are
  higher for more metal-rich stars, this phenomenon would be even more
  pronounced in the metal-rich populations, such as NGC 6791. We find
  that mass loss on the HB may be a viable method of forming subdwarf B
  (sdB) stars both in the field and in clusters, especially when the
  metallicity is high. WIYN Open Cluster Study. IV.

Title: WOCS: Pushing the Astrometric Envelope of the Open Cluster
    NGC 188
Authors: Platais, I.; Kozhurina-Platais, V.; Demarque, P.; Girard,
   T. M.; van Altena, W. F.; Klemola, A. R.; WOCS Collaboration
Bibcode: 2000AAS...196.4203P
Altcode: 2000BAAS...32..741P
  The well-known 7-Gyr-old open cluster NGC 188 has been a subject of
  numerous studies. It is also a cornerstone cluster for the WIYN Open
  Cluster Study (WOCS) project which aims to produce a comprehensive
  photometric, astrometric, and spectroscopic database for selected
  fundamental open clusters. The astrometric aspects of WOCS benefit from
  deep KPNO and CTIO 4m telescope old material in combination with the
  NOAO CCD Mosaic Imager frames. The latter presents a certain challenge
  to obtain astrometric grade positions (see accompanying poster on the
  CCD Mosaic's geometry). As an example of WOCS potential we present
  the first results of BV photometry and new proper motions of NGC 188
  down to V=21 mag. We show that there are some cluster members, mostly
  faint ones, beyond the adopted tidal radius and that the Present Day
  Mass Function (PDMF) strongly differs from the traditionally accepted
  shape of the IMF. Hopefully, the WOCS results will trigger more work
  on N-body simulations from which the IMF can be reconstructed using the
  observed PDMF. This study is supported in part by NSF grant AST9819777
  to Yale University and NSF grant AST9530632 to UCO/Lick Observatory.

Title: α Centauri AB
Authors: Guenther, D. B.; Demarque, P.
Bibcode: 2000ApJ...531..503G
Altcode:
  Detailed models of α Centauri A and B based on the Hipparcos, Yale,
  and Söderhjelm parallaxes are compared. The consequences of the
  uncertainty in mass, luminosity, surface temperature, and composition
  on the structure and the p-mode pulsation spectrum of the models
  are presented. All of the models were constructed using the most
  current stellar structure physics available to us, including helium
  and heavy-element diffusion, OPAL (Lawrence Livermore Opacity Library)
  equation of state, and OPAL and Alexander opacities. Self-consistent
  models of α Cen A and B that satisfy the observational constraints have
  an initial helium mass fraction Y<SUB>ZAMS</SUB>=~0.28. The age of the
  system depends critically on whether or not α Cen A has a convective
  core. If it does (our best model), then α Cen AB is ~7.6 Gyr old,
  and if it does not, then the binary system is ~6.8 Gyr old. Both ages
  and Y<SUB>ZAMS</SUB> are accurate to +/-~10% owing to observational
  uncertainties. The Galactic enrichment parameter (ΔY/ΔZ) for our
  best model pair is less than 1. Pulsation analyses of our best models
  yield an average large and small spacing of 101+/-3 μHz and 4.6+/-0.4
  μHz, respectively, for α Cen A, and 173+/-6 μHz and 15+/-1 μHz for
  α Cen B. Some methodologies that use p-mode frequency observations
  to constrain the system further are outlined. We include a simple
  test to determine whether or not α Cen A has a convective core and
  introduce a method to use the small frequency spacing to determine
  the age of system, overcoming the limitation that it is also sensitive
  to composition.

Title: The Metallicity Dependence of RR Lyrae Absolute Magnitudes
    from Synthetic Horizontal-Branch Models
Authors: Demarque, Pierre; Zinn, Robert; Lee, Young-Wook; Yi, Sukyoung
Bibcode: 2000AJ....119.1398D
Altcode: 1999astro.ph.12226D
  A grid of synthetic horizontal-branch (SHB) models based on
  horizontal-branch (HB) evolutionary tracks with improved physics
  has been constructed to reconsider the theoretical calibration
  of the dependence of M<SUB>v</SUB>(RR) on metallicity in globular
  clusters and the slope of the mean &lt;M<SUB>V</SUB>(RR)&gt;-[Fe/H]
  relation. The SHB models confirm Lee's earlier finding that the
  slope of the &lt;M<SUB>V</SUB>(RR)&gt;-[Fe/H] relation is itself a
  function of the metallicity range considered and that, in addition,
  for a given [Fe/H] RR Lyrae luminosities depend on HB morphology. This
  is due to the fact that HB stars pass through the RR Lyrae instability
  strip at different evolutionary stages, depending on their original
  position on the HB. At [Fe/H]=-1.9, and for HB type 0, the models
  yield M<SUB>V</SUB>(RR)=0.47+/-0.10. The mean slope for the zero-age
  HB models is 0.204. Since there is no simple universal relation
  between M<SUB>v</SUB>(RR) and metallicity that is applicable to
  all globular clusters, the HB morphology of each individual cluster
  must be taken into account, in addition to [Fe/H], in deriving the
  appropriate M<SUB>v</SUB>(RR). Taking HB morphology into account,
  we find that the slope of the mean &lt;M<SUB>V</SUB>(RR)&gt;-[Fe/H]
  relation varies between 0.36 for the clusters with Galactocentric
  distances R<SUB>gc</SUB> less than 6 kpc and 0.22 for clusters with
  6 kpc&lt;R<SUB>gc</SUB>&lt;=20 kpc. Implications for interpreting
  observations of field RR Lyrae variables and for absolute globular
  cluster ages and Galactic chronology are briefly discussed.

Title: Evolutionary Model and Oscillation Frequencies for α Ursae
Majoris: A Comparison with Observations
Authors: Guenther, D. B.; Demarque, P.; Buzasi, D.; Catanzarite, J.;
   Laher, R.; Conrow, T.; Kreidl, T.
Bibcode: 2000ApJ...530L..45G
Altcode:
  Inspired by the observations of low-amplitude oscillations of α
  Ursae Majoris A by Buzasi et al. using the WIRE satellite, a grid of
  stellar evolutionary tracks has been constructed to derive physically
  consistent interior models for the nearby red giant. The pulsation
  properties of these models were then calculated and compared with the
  observations. It is found that, by adopting the correct metallicity
  and for a normal helium abundance, only models in the mass range of
  4.0-4.5 M<SUB>solar</SUB> fall within the observational error box for
  α UMa A. This mass range is compatible, within the uncertainties,
  with the mass derived from the astrometric mass function. Analysis of
  the pulsation spectra of the models indicates that the observed α UMa
  oscillations can be most simply interpreted as radial (i.e., l=0) p-mode
  oscillations of low radial order n. The lowest frequencies observed
  by Buzasi et al. are compatible, within the observational errors, with
  model frequencies of radial orders n=0, 1, and 2 for models in the mass
  range of 4.0-4.5 M<SUB>solar</SUB>. The higher frequencies observed can
  also be tentatively interpreted as higher n-valued radial p-modes, if
  we allow that some n-values are not presently observed. The theoretical
  l=1, 2, and 3 modes in the observed frequency range are g-modes with a
  mixed mode character, that is, with p-mode-like characteristics near the
  surface and g-mode-like characteristics in the interior. The calculated
  radial p-mode frequencies are nearly equally spaced, separated by
  2-3 μHz. The nonradial modes are very densely packed throughout the
  observed frequency range and, even if excited to significant amplitudes
  at the surface, are unlikely to be resolved by the present observations.

Title: Precision Photometry of Key Open Clusters
Authors: Sarajedini, Ata; Deliyannis, Constantine; Bailyn, Charles;
   Mathieu, Robert; Demarque, Pierre
Bibcode: 2000noao.prop..312S
Altcode:
  We propose to carry out wide-field imaging observations of 8 open
  clusters which are an important part of the WIYN Open Cluster
  Study. These data will allow us to construct high precision
  color-magnitude diagrams for the clusters, which will then be used
  to investigate a number of astrophysical questions. In addition to
  publication in refereed journals, the detailed data will be made
  available to the community as part of the WIYN Open Cluster Study
  database. The number of filters, spatial coverage, and precision of
  the data we propose to obtain constitutes a substantial improvement
  over previous studies of these, and most other, open clusters.

Title: The WIYN open Cluster Study: A test of convective overshoot
    and the age of NGC 752
Authors: Kozhurina-Platais, V.; Platais, I.; Demarque, P.; Yong, H.;
   Lee, J.; Sarajedini, A.
Bibcode: 2000ASPC..198...79K
Altcode: 2000scac.conf...79K
  No abstract at ADS

Title: The WIYN Open Cluster Study and a Distance Scale
Authors: Platais, I.; Girard, T.; van Altena, W.; Koshurina-Platais,
   V.; Demarque, P.
Bibcode: 2000IAUJD..13E..17P
Altcode:
  The WIYN consortium (Wisconsin, Indiana, Yale and NOAO) astronomers
  have started the WIYN Open Cluster Study (WOCS) with the goals of 1)
  producing comprehensive photometric, astrometric and spectroscopic
  data for selected fundamental open clusters, and 2) addressing key
  problems in astrophysics, stellar dynamics and star formation. These
  fundamental clusters were selected to cover a wide range of ages,
  metallicity and location in the Galaxy and hence be representative of
  the whole system of open clusters. The Pleiades perhaps is the most
  publicised case of disagreement between the space-based and classical
  distance determination techniques. The isochrone fitting technique
  applied to the WOCS data is expected to provide more insights on some
  other clusters showing a similar discrepancy. The open cluster NGC
  2451 is of particular interest because it is a nearby young cluster,
  is well-sampled by Hipparcos and also appears to have the Pleiades-like
  paradigm.

Title: The WIYN open cluster study: A new color-magnitude diagram
    for M35 - a twin of the Pleiades?
Authors: von Hippel, T.; Kozhurina-Platais, V.; Platais, I.; Demarque,
   P.; Sarajedini, A.
Bibcode: 2000ASPC..198...75V
Altcode: 2000scac.conf...75V
  No abstract at ADS

Title: WIYN Open Cluster Study. II. UBVRI CCD Photometry of the Open
    Cluster NGC 188
Authors: Sarajedini, Ata; von Hippel, Ted; Kozhurina-Platais, Vera;
   Demarque, Pierre
Bibcode: 1999AJ....118.2894S
Altcode:
  We present high-precision UBVRI CCD photometry of the old open cluster
  NGC 188. Our color-magnitude diagram extends from near the red giant
  branch tip to as faint as ~5 mag below the main-sequence turnoff. From
  an analysis of these data along with published photometry for M67,
  we draw the following conclusions: (1) From the UBV two-color
  diagram, we find a reddening of E(B-V)=0.04+/-0.02 for M67 and
  E(B-V)=0.09+/-0.02 for NGC 188. (2) Based on main-sequence fitting
  to solar abundance isochrones, the distance moduli turn out to be
  (m-M)<SUB>v</SUB>=9.69+/-0.11 for M67 and (m-M)<SUB>v</SUB>=11.44+/-0.08
  for NGC 188. (3) The comparison of the CMDs to theoretical isochrones
  indicates that an amount of core convective overshoot equivalent to 0.10
  of a pressure scale height is appropriate for M67, while no overshoot
  is required to fit the CMD of NGC 188. These isochrones suggest that NGC
  188 is 3.0+/-0.7 Gyr older than M67. (4) There is a clear indication of
  mass segregation in both M67 and NGC 188, with the most massive stars
  (M/M<SUB>solar</SUB>&gt;1.1) being more centrally concentrated than
  those that are the least massive (0.8&gt;=M/M<SUB>solar</SUB>&gt;0.65).

Title: The Pulsation Properties of Procyon A
Authors: Chaboyer, Brian; Demarque, P.; Guenther, D. B.
Bibcode: 1999ApJ...525L..41C
Altcode: 1999astro.ph..9015C
  A grid of stellar evolution models for Procyon A has been
  calculated. These models include the best physics available to us
  (including the latest opacities and equation of state) and are based on
  the revised astrometric mass of Girard et al. Models were calculated
  with helium diffusion and with the combined effects of helium and
  heavy-element diffusion. Oscillation frequencies for l=0, 1, 2, and
  3 p-modes and the characteristic period spacing for the g-modes were
  calculated for these models. We find that g-modes are sensitive to model
  parameters that effect the structure of the core, such as convective
  core overshoot, the heavy-element abundance, and the evolutionary state
  (main sequence or shell hydrogen burning) of Procyon A. The p-modes
  are relatively insensitive to the details of the physics used to model
  Procyon A and only depend on the evolutionary state of Procyon A. Hence,
  observations of p-mode frequencies on Procyon A will serve as a robust
  test of stellar evolution models.

Title: Toward a Pop II Mass-Luminosity Relation
Authors: Rubenstein, Eric P.; Orosz, Jerome A.; Deliyannis,
   Constantine; Demarque, Pierre
Bibcode: 1999noao.prop..116R
Altcode:
  The observing runs contained within this proposal are part of a
  long term goal of constraining the variation of the Mass-Luminosity
  Relation as a function of composition. Using a sequence of Mosaic II
  images (U,V,R,I &amp; H-alpha) we propose to make a detailed study of
  binaries and the general population of 2 globular clusters and three
  open clusters. The specific clusters were selected to have a wide range
  of chemical composition, from -2.2 &lt;=[Fe/H]&lt;=0.2. I will make a
  sensitive search for main-sequence binary stars, blue straggler stars,
  SX Phe pulsators and cataclysmic variables and construct a precise CMD
  to search for evidence of a binary sequence. The luminosity function
  of M30 will be compared with that derived from my team's HST data of
  that cluster's core (HST-GO-7379). Comparison of these two data sets,
  combined with Yale stellar evolutionary models (with co-I Demarque) will
  allow me to study the degree of mass segregation in this dynamically
  evolved cluster. As part of my ongoing project to constrain the Pop II
  Mass-Luminosity Relation (NSF-9902667) I will follow-up the detection
  of any detached main-sequence binaries with spectroscopic observations
  (with co-Is Orosz &amp; Deliyannis) to determine the masses of the
  components. We also propose to obtain spectroscopic observations of
  an uncrowded binary candidate detected during previous work on NGC
  6752. If this object and other binaries we hope to detect are double-
  lined spectroscopic binaries, our observations of radial velocity
  variations will allow the precise determination of masses. Single-lined
  spectroscopic binaries will allow us to derive the mass-ratio of the
  systems and begin to constrain the unknown mass-ratio distribution of
  binaries in clusters. I will be spending this coming year at CTIO on
  an NSF fellowship specifically to pursue this project.

Title: Helioseismology: Probing the Interior of a Star
Authors: Demarque, P.; Guenther, D. B.
Bibcode: 1999PNAS...96.5356D
Altcode:
  Helioseismology offers, for the first time, an opportunity to probe in
  detail the deep interior of a star (our Sun). The results will have a
  profound impact on our understanding not only of the solar interior,
  but also neutrino physics, stellar evolution theory, and stellar
  population studies in astrophysics.

Title: The Run of Superadiabaticity in Stellar Convection
    Zones. II. Effect of Photospheric Convection on Solar p-Mode
    Frequencies
Authors: Demarque, Pierre; Guenther, D. B.; Kim, Yong-Cheol
Bibcode: 1999ApJ...517..510D
Altcode:
  Kim and Chan have completed a three-dimensional numerical simulation
  of the interaction between turbulent convection and radiation in and
  above the highly superadiabatic layer (SAL) in the Sun. They have shown
  that the dynamics of the domain dictates a SAL structure different from
  that of a traditional hydrostatic solar model. The top boundary of the
  convection zone is moved outward by about 0.3 pressure scale height, and
  in addition, convective overshoot extends into the radiative atmosphere
  layers by 0.45 pressure scale height. Using our one-dimensional stellar
  evolution code, we have studied the sensitivity of the calculated
  p-mode frequencies to a modification of the SAL structure similar to
  that predicted by Kim and Chan. We find that it is possible to remove
  in this way the main discrepancy between observed and calculated
  p-mode frequencies. This experiment is a promising first step in the
  use of physically realistic three-dimensional radiative-hydrodynamic
  numerical simulations to derive reliable surface boundary conditions
  for one-dimensional stellar models.

Title: The Ultraviolet Upturn in Elliptical Galaxies as an Age
    Indicator
Authors: Yi, Sukyoung; Lee, Young-Wook; Woo, Jong-Hak; Park, Jang-Hyun;
   Demarque, Pierre; Oemler, Augustus, Jr.
Bibcode: 1999ApJ...513..128Y
Altcode: 1998astro.ph.10022Y
  The UV upturn phenomenon in elliptical galaxies, although challenging
  because of its complexity, is attractive for its potential value as
  an age indicator of old stellar systems. This work represents the
  combined efforts of two population synthesis groups with substantially
  different views to work together to minimize uncertainties in modeling
  and analysis. Unfortunately, this study, using the currently available
  data, cannot determine the metallicity of the dominant UV sources, one
  of the most outstanding problems related to the UV upturn phenomenon,
  as some input parameters need to be constrained better. We have found,
  however, that it is feasible to select a more likely model empirically
  because different models predict substantially different UV-to-V flux
  ratios as functions of redshift: metal-rich solutions predict a much
  steeper decline in the UV-to-V flux ratio than metal-poor solutions. We
  show that such differences in model predictions are quite independent
  of cosmology and are detectable using current and upcoming space UV
  facilities. The various alternatives suggest significantly different
  ages for the present-epoch giant ellipticals: the metal-rich solutions
  suggest 30%-50% smaller ages than the metal-poor solutions. Thus, an
  empirical fitting would not only reveal the origin of the UV upturn
  but yield independent age estimations for ellipticals. We show that
  this may effectively constrain some of the cosmological parameters
  that predict a unique age for the present-epoch galaxies. If we use
  the most recent estimations of H<SUB>0</SUB> and Ω<SUB>0</SUB>, the
  younger, metal-rich models would have no conflict with a cosmology
  of a negligibly small Λ<SUB>0</SUB>, whereas the older, metal-poor
  models unavoidably suggest a substantially large value of Λ<SUB>0</SUB>
  (i.e., Λ<SUB>0</SUB>&gt;~0.63 for z<SUB>for</SUB>=∞) in the context
  of an inflationary universe.

Title: Precision Photometry of Key Open Clusters
Authors: Sarajedini, Ata; Deliyannis, Constantine; Demarque, Pierre;
   Bailyn, Charles; von Hippel, Ted; Mathieu, Robert; van Altena, William
Bibcode: 1999noao.prop...98S
Altcode:
  We propose to carry out wide-field imaging observations of 5 open
  clusters which are an integral part of the WIYN Open Cluster
  Study. These data will allow us to construct high precision
  color-magnitude diagrams for the clusters, which will then be used
  to investigate a number of astrophysical questions. In addition to
  publication in refereed journals, the detailed data will be made
  available to the community as part of the WIYN Open Cluster Study
  database. The number of filters, spatial coverage, and precision of
  the data we propose to obtain constitutes a substantial improvement
  over previous studies of these, and most other, open clusters

Title: Which Are the Most Realistic Models to be Used?
Authors: Demarque, P.
Bibcode: 1999ASPC..173..373D
Altcode: 1999sstt.conf..373D
  No abstract at ADS

Title: Globular Cluster Ages: Overview
Authors: Demarque, P.
Bibcode: 1999ASPC..192..177D
Altcode: 1999sdsg.conf..177D
  No abstract at ADS

Title: The Search for Pulsations in the sdB Stars of NGC 6791
Authors: Yong, H.; Bailyn, C. D.; Demarque, P.
Bibcode: 1998AAS...193.6403Y
Altcode:
  Pulsations in sdB stars were predicted by Charpinet et al. (1996) and
  discovered observationally by Kilkenny et al. (1997). The theoretical
  models of Charpinet et al. suggest that the pulsation mechanism is
  enhanced with metallicity. Thus, the sdB stars in the metal rich open
  cluster NGC 6791 are good candidates for such pulsations. We present
  the results of CCD photometry taken at the WIYN Observatory of NGC
  6791. Pulsations in the sdB star B5 are found with a period of about
  101 sec. and an amplitude of 0.04 mag. in B. Both pulsation period
  and amplitude are consistent with previous observations of field sdB
  stars. This is the first detection of pulsations in a sdB star in a
  cluster environment. The detection of pulsations in sdB stars in a
  cluster gives us a unique opportunity to calculate physical properties
  of sdB stars (such as the core mass) through comparison with theoretical
  models. This may also give us the opportunity to independently determine
  the metallicity and initial helium content of NGC 6791.

Title: The search for pulsations in the sdB stars of NGC 6791.
Authors: Yong, H.; Bailyn, C. D.; Demarque, P.
Bibcode: 1998BAAS...30.1338Y
Altcode:
  No abstract at ADS

Title: Testing the Constancy of the Gravitational Constant Using
    Helioseismology
Authors: Guenther, D. B.; Krauss, L. M.; Demarque, P.
Bibcode: 1998ApJ...498..871G
Altcode:
  We compare the p-mode oscillation spectra of solar models, constructed
  under the assumption that the universal gravitation constant G varied
  monotonically over the course of the solar lifetime, to the most
  recent solar p-mode frequency observations from the Global Oscillation
  Network Group (GONG) instrument and Birmingham Solar Oscillation
  Network (BiSON). The GONG instrument consists of six telescopes
  spread over different longitude around the Earth, each recording,
  once every minute, Doppler shift images of the Sun's surface. BiSON
  also consists of a network of six telescopes specifically designed to
  observe low-l p-modes. We find that only those solar models constructed
  with (1/G)dG/dt &lt;= ~1.6 × 10<SUP>-12</SUP> yr<SUP>-1</SUP> are
  consistent with the observations. This constraint not only probes G
  over cosmic time, it is stronger by almost one order of magnitude than
  constraints on the current maximum time variation coming from radar
  ranging and binary pulsar timing measurements.

Title: The Age of Globular Clusters in Light of Hipparcos: Resolving
    the Age Problem?
Authors: Chaboyer, Brian; Demarque, P.; Kernan, Peter J.; Krauss,
   Lawrence M.
Bibcode: 1998ApJ...494...96C
Altcode: 1997astro.ph..6128C
  We review five independent techniques that are used to set the distance
  scale to globular clusters, including subdwarf main-sequence fitting
  utilizing the recent Hipparcos parallax catalog. These data together
  all indicate that globular clusters are farther away than previously
  believed, implying a reduction in age estimates. We now adopt a best-fit
  value M<SUB>v</SUB> (RR Lyrae stars) = 0.39 +/- 0.08 (statistical) at
  [Fe/H] = -1.9 with an additional uniform systematic uncertainty of
  <SUP>+0.13</SUP><SUB>-0.18</SUB>. This new distance scale estimate
  is combined with a detailed numerical Monte Carlo study (previously
  reported by Chaboyer et al.) designed to assess the uncertainty
  associated with the theoretical age-turnoff luminosity relationship in
  order to estimate both the absolute age and uncertainty in age of the
  oldest globular clusters. <P />Our best estimate for the mean age of the
  oldest globular clusters is now 11.5 +/- 1.3 Gyr, with a one-sided 95%
  confidence level lower limit of 9.5 Gyr. This represents a systematic
  shift of over 2 σ compared to our earlier estimate, owing completely
  to the new distance scale--a shift which we emphasize results not only
  from the Hipparcos data. This now provides a lower limit on the age of
  the universe that is consistent with either an open universe or with
  a flat matter-dominated universe (the latter requiring H<SUB>0</SUB>
  &lt;= 67 km s<SUP>-1</SUP> Mpc<SUP>-1</SUP>). Our new study also
  explicitly quantifies how remaining uncertainties in the distance
  scale and stellar evolution models translate into uncertainties in
  the derived globular cluster ages. Simple formulae are provided that
  can be used to update our age estimate as improved determinations
  for various quantities become available. Formulae are also provided
  that can be used to derive the age and its uncertainty for a globular
  cluster, given the absolute magnitude of the turnoff or the point on
  the subgiant branch 0.05 mag redder than the turnoff.

Title: The internal structure and age of the sun from seismology
Authors: Demarque, P.; Guenther, D. B.; Kim, Y. -C.
Bibcode: 1998ASPC..138...79D
Altcode: 1998stas.conf...79D
  No abstract at ADS

Title: The Evolution of Procyon A
Authors: Chaboyer, B.; Demarque, P.; Guenther, D. B.
Bibcode: 1998ASPC..135...67C
Altcode: 1998hcsp.conf...67C; 1997astro.ph.10034C
  A grid of stellar evolution models for Procyon A have been
  calculated. These models include the best physics available to us
  (including the latest opacities and equation of state) and are based
  on the revised astrometric mass of Girrard et al. (1996, BAAS, 28,
  919). The long standing descrepency between the evolutionary mass and
  the astometric mass is now resolved, a result of the newly determined
  astrometric mass. Models were calculated with helium diffusion and with
  the combined effects of helium and heavy element diffusion. Oscillation
  frequencies for l=0,1,2 and 3 p-modes (and g-modes) were calculated
  for these models, and we discuss how future obsevations of p-modes in
  Procyon may be used to constrain the stellar evolution models and the
  evolutionary stage of Procyon A.

Title: On the Origin of the Ultraviolet Upturn in Elliptical
    Galaxies. II. Test of the Horizontal Branch Hypothesis
Authors: Yi, Sukyoung; Demarque, Pierre; Oemler, Augustus, Jr.
Bibcode: 1998ApJ...492..480Y
Altcode: 1997astro.ph..8185Y
  Whether or not metal-rich HB stars are the dominant UV source in
  giant elliptical galaxies (GEs) is an important question in current
  astronomical research. We follow up our previous evolutionary
  population synthesis study with quantitative tests to answer this
  question affirmatively under the following three conditions: (1)
  Reimers's empirical mass-loss formula is proper, (2) the mass-loss
  efficiency parameter η in metal-rich stars is somewhat larger
  than the value estimated from the metal-poor star studies, and
  (3) the true value of the helium-enrichment parameter (ΔY/ΔZ) is
  positive. All three important empirical characteristics of the UV
  upturn (i.e., the fact that strong UV upturns are restricted to GEs,
  the positive UV upturn-metallicity correlation, and the narrow range
  of the T<SUB>eff</SUB> of the UV sources) are closely reproduced for
  reasonable ranges of input parameters. We discuss the major sources
  of uncertainties in the models, such as the production and role of
  hot horizontal-branch stars in GEs, and the importance of galactic
  nucleosynthesis.

Title: Report from Working Group Session 2: Seismology of Sun-like
Stars: Techniques and Strategies
Authors: Demarque, P.
Bibcode: 1998ESASP.418..413D
Altcode: 1998soho....6..413D
  No abstract at ADS

Title: Testing the Constancy of Newton's Gravitational Constant
    using Helioseismology
Authors: Guenther, D. B.; Demarque, P.; Krauss, L. M.
Bibcode: 1998ESASP.418..469G
Altcode: 1998soho....6..469G
  Using low-l p-mode oscillation data from GONG and BiSON, and solar
  models constructed with a varying gravitational constant G, we are
  able to set limits on the maximum allowable monotonic variation in G
  during the current epoch. The helioseismic limit is almost an order
  of magnitude tighter than previously established limits using radar
  ranging and binary pulsar timing (Guenther et al. 1998) This research
  was supported in part by NSERC, to DBG, and DOE, to LMK.

Title: Testing Models of the Solar Highly Superadiabatic Layer
    with Seismology
Authors: Demarque, P.; Guenther, D. B.; Kim, Y. -C.
Bibcode: 1998ESASP.418..699D
Altcode: 1998soho....6..699D
  The discrepancy between the computed and observed solar p-mode
  frequencies can be used to determine which parts of the solar model
  needs improvement. The increase of the discrepancy toward higher
  frequencies reveals that the problem lies near the surface (Guenther
  1994). Solar models constructed in the standard way with radiative
  atmospheres and using the mixing length approximation do not represent
  faithfully the structure of the photospheric and highly superadiabatic
  subphotospheric layers of the Sun. Recent 3D numerical simulations
  of radiative hydrodynamics in the solar outer convection zone and
  atmosphere by Kim &amp; Chan (1998) show that there is convective
  overshoot into the atmosphere and that the convection zone top boundary
  is moved outward. Guided by these results we study the sensitivity
  of the p-mode frequencies to outward shifts in the position of the
  convection zone top boundary. This research was supported in part by
  grants from NASA (PD), NSERC (DBG) and the Korean Scientific Research
  Agency (YCK).

Title: Mass Loss on the Horizontal Branch
Authors: Yong, H.; Demarque, P.; Yi, S.
Bibcode: 1997AAS...191.1209Y
Altcode: 1997BAAS...29.1229Y
  Mass loss is an important mechanism in various stages of stellar
  evolution. Despite this, mass loss remains one of the more poorly
  understood aspects of stellar evolution. We present preliminary
  results of a systematic study of mass loss effects on the evolution
  of horizontal branch stars. Since mass loss is poorly understood,
  the simplest approach was taken. Several constant mass loss rates of
  {10(-9) , 3 x 10(-9}) , and {10(-10}) {M<SUB>sun</SUB> yr(-1}) were
  assumed in the evolution of horizontal branch stars and compared to
  those with no mass loss. Horizontal branch models were constructed
  with envelope masses ranging from {0.005 M<SUB>sun</SUB>} to {0.46
  M<SUB>sun</SUB>}. While it is unclear whether mass loss occurs at all
  on the horizontal branch, we examine its effects, first, to attempt
  to explain the origin of some extreme blue horizontal branch stars and
  second, to constrain mass loss rates on the horizontal branch. We also
  study the effect it has in stars of different metallicities. Preliminary
  results suggest that mass loss tends to evolve stars blueward in the
  HR diagram in comparison to their normal course of evolution. This
  effect is somewhat enhanced with larger metallicities.

Title: The Relative Ages of Galactic Globular Clusters
Authors: Sarajedini, A.; Chaboyer, B.; Demarque, P.
Bibcode: 1997PASP..109.1321S
Altcode: 1997astro.ph.10245S
  We present a review of the present state of knowledge regarding the
  relative ages of Galactic globular clusters. First, we discuss the
  relevant galaxy formation models and describe the detailed predictions
  they make with respect to the formation timescale and chemical evolution
  of the globular clusters. Next, the techniques used to estimate globular
  cluster ages are described and evaluated with particular emphasis on the
  advantages and disadvantages of each method. With these techniques as a
  foundation, we present arguments in favor of the following assertions:
  1) The age of a globular cluster is the likeliest candidate to be the
  global second parameter, which along with metal abundance, controls
  the morphology of the horizonal branch. 2) A total age range of as
  much as ~ 5 Gyr exists among the bulk of the Galactic globulars. 3)
  There is a significant relation between age and metallicity among the
  Galactic globular clusters if the slope of the \mvrr-\feh\ relation is
  less than ~ 0.23. These conclusions along with other supporting evidence
  favor a formation scenario in which the inner regions of the Galactic
  halo collapsed in a monotonic fashion over a short time period much
  less than 1 Gyr. In contrast, the outer regions of the halo fragmented
  and collapsed in a chaotic manner over several Gyrs. (SECTION: Invited
  Review Articles)

Title: Evolution of Stellar Collision Products in Globular
    Clusters. I. Head-on Collisions
Authors: Sills, Alison; Lombardi, James C., Jr.; Bailyn, Charles D.;
   Demarque, Pierre; Rasio, Frederic A.; Shapiro, Stuart L.
Bibcode: 1997ApJ...487..290S
Altcode: 1997astro.ph..5019S
  We explore the evolution of collisionally merged stars in the blue
  straggler region of the H-R diagram. The starting models for our
  stellar evolution calculations are the results of the smoothed
  particle hydrodynamics (SPH) simulations of parabolic collisions
  between main-sequence stars performed by Lombardi, Rasio, &amp;
  Shapiro. Since SPH and stellar evolution codes employ different and
  often contradictory approximations, it is necessary to treat the
  evolution of these products carefully. The mixture and disparity of
  the relevant timescales (hydrodynamic, thermal relaxation, and nuclear
  burning) and of the important physical assumptions between the codes
  makes the combined analysis of the problem challenging, especially
  during the initial thermal relaxation of the star. In particular,
  the treatment of convection is important and semiconvection must be
  modeled in some detail. <P />The products of seven head-on collisions
  are evolved through their initial thermal relaxation and then through
  the main-sequence phase to the base of the giant branch. Their
  evolutionary tracks are presented. In contrast to what was assumed
  in previous work, these collision products do not develop substantial
  convective regions during their thermal relaxation and therefore are
  not mixed significantly after the collision.

Title: On the Origin of the UV Upturn in Elliptical
    Galaxies. I. Sensitivity of UV Population Synthesis to Various
    Input Parameters
Authors: Yi, Sukyoung; Demarque, Pierre; Oemler, Augustus, Jr.
Bibcode: 1997ApJ...486..201Y
Altcode: 1997astro.ph..5173Y
  We present models of the late stages of stellar evolution intended to
  explain the ``UV upturn'' phenomenon in elliptical galaxies. Such models
  are sensitive to values of a number of poorly constrained physical
  parameters, including metallicity, age, stellar mass loss, helium
  enrichment, and the distribution of stars on the zero-age horizontal
  branch (HB). We explore the sensitivity of the results to values
  of these parameters and reach the following conclusions. <P />Old,
  metal-rich galaxies, such as giant ellipticals, naturally develop a UV
  upturn within a reasonable timescale--less than a Hubble time--without
  the presence of young stars. The most likely stars to dominate the
  UV flux of such populations are low-mass, core helium-burning (HB
  and evolved HB) stars. Metal-poor populations produce a higher ratio
  of UV-to-V flux, owing to opacity effects, but only metal-rich stars
  develop a UV upturn, in which the flux increases toward shorter UV
  wavelengths.

Title: Seismic Tests of the Sun's Interior Structure, Composition,
    and Age, and Implications for Solar Neutrinos
Authors: Guenther, D. B.; Demarque, P.
Bibcode: 1997ApJ...484..937G
Altcode:
  The structure of the deep interior of a variety of standard and
  nonstandard solar models constrained by the low-l p-mode oscillation
  data from GONG are presented. For standard models, we show that the
  effects of both helium and heavy-element diffusion must be included in
  order to find simultaneous agreement with both the p-mode spectrum and
  the observed value of (Z/X)<SUB>⊙</SUB>. Related to this conclusion,
  we find that the average interior heavy-element abundance is greater
  than the observed surface abundance in models whose small spacings,
  which are derived from the p-mode oscillation spectra, best match the
  observations. The high-quality data from the Global Oscillation Network
  Group (GONG) now permit a precise determination of the seismic age of
  the Sun. The best agreement with the calculated oscillation spectra
  is achieved for 4.5 +/- 0.1 Gyr, an age closely consistent with the
  age of the Sun inferred from meteorites, i.e., 4.53 +/- 0.04 Gyr. This
  result lends strong support to the standard assumption of the theory
  of stellar evolution. With regard to the nonstandard solar models, we
  set limits on the extent to which the nonstandard assumptions can be
  applied to the model while still being consistent with the observed
  p-modes. The nonstandard assumptions investigated here are: forced
  mixing in the core, forced mixing in a shell surrounding the core, and
  near-zero heavy-element abundance in the core. These assumptions were
  selected because at one time or another they have all been proposed
  to reduce the neutrino flux of the solar model, thereby bringing the
  flux of the model more in line with the observed flux. All nonstandard
  models include helium and heavy element diffusion. We confirm, now using
  the latest solar model physics, that these nonstandard assumptions,
  when capable of reducing significantly the solar neutrino flux,
  perturb the interior structure too much to be consistent with p-mode
  observations. In addition, we set strict limits on the extent to which
  these nonstandard assumptions are tolerated by the current p-mode
  observations. For example, we show that the p-mode small spacings
  are incompatible with a low-Z core larger than 0.06 M<SUB>⊙</SUB>
  in the Sun. And we show that if the Sun's core is chemically mixed,
  the extent of the mixed core cannot exceed 0.02 M<SUB>⊙</SUB>. The
  seismic data are also incompatible with extensive rapid mixing of
  <SUP>4</SUP>He in the solar envelope. This, we believe, also argues
  against the possibility of slow mixing of <SUP>3</SUP>He occurring
  in a shell, as was recently proposed by Cumming and Haxton to lower
  the <SUP>7</SUP>Be/<SUP>8</SUP>B neutrino flux ratio. But we note
  that the occurrence of some mixing of <SUP>3</SUP>He and other trace
  elements and isotopes in the region of the solar interior where the
  initial <SUP>4</SUP>He abundance is nearly uniform (which could not
  at this point be detected by seismology) might modify the calculated
  neutrino fluxes.

Title: On the Ultraviolet-bright Phase of Metal-rich Horizontal-Branch
    Stars
Authors: Yi, Sukyoung; Demarque, Pierre; Kim, Yong-Cheol
Bibcode: 1997ApJ...482..677Y
Altcode: 1997astro.ph..5111Y
  We consider the origin of the UV-bright phase of metal-rich
  helium-burning stars, the slow blue phase (SBP) that was predicted
  by various earlier works. Based on improved physics including
  OPAL opacities, which is the same physics that was used in the
  construction of the new Yale Isochrones, we confirm the existence of
  the SBP. In addition to our grid of evolutionary tracks, we provide
  an analytical understanding of the main characteristics of the SBP
  phenomenon. <P />The SBP is slow because it is a slow-evolving,
  helium-shell-burning phase that is analogous to the early asymptotic
  giant branch phase. The SBP of a more metal-rich star is slower than a
  metal-poor counterpart if they have the same T<SUB>eff</SUB> because a
  more metal-rich helium-burning star has a smaller mass than a metal-poor
  one and because lifetime increases as mass decreases. <P />Metal-rich
  helium-burning stars easily become hot because the luminosity from the
  hydrogen-burning shell is extremely sensitive to the mean molecular
  weight μ, whereas the luminosity from the helium-burning core is
  not. Under the assumption of a positive ΔY/ΔZ, helium abundance
  plays the most important role in governing μ, and thus Dorman et
  al. found that the SBP occurs only when Y &gt;~ 0.4 when ΔY/ΔZ
  &gt;~ 0. We suggest that the SBP phenomenon is a major cause of the
  UV upturn phenomenon in giant elliptical galaxies, as will be shown
  in subsequent papers. The new HB tracks can be retrieved from S. Y.'s
  web site http://shemesh.gsfc.nasa.gov/astronomy.html.

Title: The Age of NGC 3680 and a Test of Convective Overshoot
Authors: Kozhurina-Platais, Vera; Demarque, Pierre; Platais, Imants;
   Orosz, Jerome A.; Barnes, Sydney
Bibcode: 1997AJ....113.1045K
Altcode:
  A new CCD BV color-magnitude diagram has been derived for the
  intermediate age open cluster NGC 3680. The quality of photometry
  coupled with the best-to-date knowledge of cluster memberships allows
  for a detailed isochrone fit to the CMD. The theoretical isochrones
  have been constructed using the Yale Rotating Evolution Code (YREC)
  in its non-rotating mode and the OPAL opacities (circa 1991). Four
  sets of isochrones have been calculated: one for the standard stellar
  model calibrated to the Sun and three others for models with different
  amounts of convective overshoot at the edge of the convective core,
  namely, 0.15, 0.20 and 0.25H<SUB>p</SUB>, where H<SUB>p</SUB>
  is the pressure scale height at the core edge. All four sets of
  theoretical isochrones were adjusted to an adopted distance modulus of
  V<SUB>deg</SUB>-M<SUB>V</SUB>=10.20 and reddening E(B-V)=0.075 which
  leads to ages of 1.3+/-0.15, 1.5+/-0.15, 1.6+/-0.15 and 1.7+/-0.15
  Gyr, respectively. The uncertainties in age mainly reflect a subjective
  decision in differentiating a good fit from a poorer one. The model with
  a convective overshoot of 0.20H<SUB>p</SUB> seems to yield the best fit
  to the sharply curved upper main-sequence. Hence, the estimated age of
  NGC 3680 is 1.6+/-0.15 Gyr. The adopted overshoot parameter ostensibly
  is uncertain by +/-0.05H_p. For comparison, the same stellar models
  with overshoot of 0.25H<SUB>p</SUB> were fit to the color-magnitude
  diagram of the cluster NGC 752, which is similar in age and composition
  to NGC 3680. The age estimate for NGC 752 is 1.6+/-0.2 Gyr, assuming
  V<SUB>deg</SUB>-M<SUB>V</SUB>=8.20 and E(B-V)=0.030 for the cluster.

Title: The Run of Superadiabaticity in Stellar Convection
    Zones. I. The Sun
Authors: Demarque, P.; Guenther, D. B.; Kim, Y. -C.
Bibcode: 1997ApJ...474..790D
Altcode:
  The effect of adjustments to the superadiabatic layer (SAL)
  in a model of the Sun on the p-mode oscillation frequencies has
  been studied. Numerical simulations of solar convection by Kim and
  coworkers have shown that the usual mixing length approximation (MLA)
  overestimates the convective efficiency in the SAL. To correct for
  the overestimated convective efficiency in the calculation of the
  temperature gradient and the mean structure of the SAL, we have adopted
  a variable mixing length parameter, which decreases as the surface
  is approached, based on a simple parameterization suggested by the
  simulations. We find that these changes to the structure of the SAL
  reduce the discrepancies between observed and calculated oscillation
  frequencies in the low to intermediate l range.

Title: The Ages of Globular Star Clusters
Authors: Demarque, Pierre
Bibcode: 1997eds..proc...30D
Altcode:
  A summary of the chronology of the Galaxy is presented. The best
  determined age is that of the sun, near 4.5 Gyr, which is derived by
  combining the radioactive age of the solar system with our knowledge
  of the premain sequence evolutionary timescales. It is argued that
  some open clusters, and a fraction of the disk field population may
  be as old as 10 Gyr.

Title: Evolution of Blue Stragglers
Authors: Sills, A.; Lombardi, J.; Bailyn, C.; Demarque, P.; Rasio,
   F.; Shapiro, S.
Bibcode: 1996AAS...189.7207S
Altcode: 1996BAAS...28.1366S
  Blue stragglers, stars in clusters which are bluer and brighter
  than the main sequence turnoff, were discovered over forty years
  ago. However, a definitive theory to explain their formation and
  subsequent evolution still does not exist. One currently favoured idea
  is that some blue stragglers are the products of stellar collisions. We
  have been investigating this hypothesis by combining the results
  of Smoothed Particle Hydrodynamics (SPH) simulations of the stellar
  collision (Lombardi, Rasio and Shapiro 1996) with stellar evolution
  calculations. We convert the results of the SPH simulations into a
  starting model for our evolution calculations, and then evolve the
  resulting star through the initial thermal relaxation phase to the main
  sequence, up the giant branch, and onto the horizontal branch. In this
  way we can determine lifetimes and distributions of blue stragglers
  in globular clusters without resorting to previously-employed ad
  hoc assumptions (eg. Bailyn and Pinsonneault 1995, Ouellette and
  Prichet 1996, Sandquist, Bolte and Hernquist 1996). The difficulties
  of converting the results of a hydrodynamic calculation into a starting
  model for a stellar evolution code which assumes hydrostatic equilibrium
  will be discussed, and preliminary results will be presented. Bailyn,
  C. D. and Pinsonneault, M. H. 1995, ApJ, 439, 705. Lombardi, J. C.,
  Rasio, F. A. and Shapiro, S.L. 1996 ApJ, 468, 797. Ouellette, J. and
  Prichet, C. 1996, in The Origins, Evolution and Destinies of Binary
  Stars in Globular Clusters, ed. E. F. Milone, p 356. Sandquist, Bolte
  and Hernquist, 1996, ApJ in press.

Title: An accurate relative age estimator for globular clusters.
Authors: Chaboyer, B.; Demarque, P.; Kernan, P. J.; Krauss, L. M.;
   Sarajedini, A.
Bibcode: 1996MNRAS.283..683C
Altcode:
  Globular cluster age estimates based on the absolute magnitude of the
  main-sequence turn-off [M<SUB>v</SUB>(TO)] are generally considered
  to be the most reliable from a theoretical viewpoint. However, the
  difficulty in determining M<SUB>v</SUB>(TO) in observed colour-magnitude
  diagrams leads to a large error in the derived age. In this paper, the
  authors advocate the use of the absolute magnitude of the point which
  is brighter than the turn-off and 0.05 mag redder [M<SUB>v</SUB>(BTO)]
  as a precision age indicator. It is easy to measure this point on
  observed colour-magnitude diagrams, leading to small observational
  error bars. Furthermore, an extensive Monte Carlo calculation indicates
  that the theoretical uncertainty in M<SUB>v</SUB>(BTO) is similar to
  M<SUB>v</SUB>(TO). As a result, ages derived using M<SUB>v</SUB>(BTO)
  are at least a factor of 2 more precise than those derived using
  M<SUB>v</SUB>(TO). This technique is applied to the globular cluster
  M68 and an age of 12.8±0.3 Gyr is derived, indicating that M68 is a
  "young" globular cluster. A homogeneous set of globular cluster age
  estimates with this precision would provide unprecedented insight into
  the formation of the Galactic halo.

Title: Testing the Structure of the Solar Superadiabatic Layer
    with Seismology
Authors: Demarque, P.; Guenther, D. B.; Kim, Y. -C.
Bibcode: 1996AAS...189.1801D
Altcode: 1996BAAS...28.1297D
  Kim et al.(1995 ApJ,442,422;1996 ApJ,461,499) have recently carried
  out 3D numerical simulations of shallow convection in the Sun. These
  calculations, which apply to the transition from the inner part of the
  superadiabatic peak into the deeper adiabatic layers of the convection
  zone, treat the coupling of radiative and convective transport and
  include realistic physics in the solar model. Radiative transfer is
  treated in the diffusion approximation. The simulations show that
  the conventional mixing length formalism underestimates the ratio of
  radiative to convective transport in the outer layers of the solar
  convection zone. This effect has been simulated in the solar models by
  calculating the temperature gradient within the mixing length framework,
  adopting a variable mixing length parameter alpha . We have constructed
  standard solar models precisely tuned to the Sun, using a simple linear
  dependence of alpha on depth in the outer part of the solar convection
  zone. We show that increasing alpha with depth in this way modifies
  the structure of the superadiabatic layer in the direction of improving
  agreement between the calculated and observed solar p-mode frequencies.

Title: VizieR Online Data Catalog: Revised Yale Isochrones and
    Luminosity Functions (Green+ 1987)
Authors: Green, E. M.; Demarque, P.
Bibcode: 1996yCat.6040....0G
Altcode:
  The revised isochrones and luminosity functions (LFs) are based on the
  stellar evolution calculations of Mengel et al. (1979) and Sweigart and
  Gross (1978). The revised tables comprise the most complete (as of 1987)
  isochrone grid available in both age and composition. The improvement
  in the revised catalog is the inclusion of UBVRI data as well as the
  theoretical quantities, which are empirically matched to a wide range of
  observational UBVRI data (Green et al. 1987, unpublished). These tables
  enable users to interpolate between isochrones, to plot isochrones in
  order to fit color-magnitude diagrams, luminosity functions to compare
  with observational data, and to construct stellar population models. To
  facilitate the use of isochrones, we (at the Astronomical Data Center,
  in 1987) had made available several FORTRAN programs, ISOTRP, LF,
  and subroutines. They incorporate our experience of the best methods
  of interpolation, minimization of precision problems, and how to deal
  with compositions and ages that are not always complete. ISOTRP allows
  the user to interpolate for any helium abundance or metallicity in the
  range of the Revised Yale Isochrone tables. LF constructs customized
  differential luminosity functions for Mbol or a UBVRI magnitude, for
  any bin size, and for any initial mass functions. In addition to the
  24 isochrone files and the FORTRAN programs, we (at ADC) have included
  the color table that was used to convert from [Fe/H], log Teff, and
  log g to BC, U-B, B-V, V-R, R-I, in the isochrone data files. The data
  cover a complete grid with [Fe/H] from 1.00 to -3.5 in steps of 0.50,
  Teff from 2800 to 20000 K, and log g from 0.00 to 6.00. (26 data files).

Title: Photometry of Star Clusters Near the Galactic Center
Authors: Heasley, J.; Janes, K.; Demarque, P.; Zinn, R.
Bibcode: 1996AAS...188.0303H
Altcode: 1996BAAS...28U.821H
  Observations from the WFPC2 on the Hubble Space Telescope have
  been combined with ground-based CCD calibration frames to derive new
  color-magnitude diagrams for the globular clusters NGC 6624, NGC 6293,
  and NGC 6333. All three clusters lie in crowded fields in the direction
  of the galactic center. NGC 6624 is a metal-rich cluster ([Fe/H] =
  -0.4) thought to be part of the thick disk population, while NGC 6293
  and 6333 are metal-poor clusters ([Fe/H] = -1.9 and -1.8 respectively)
  located within 3 kpc of the galactic center. The new color-magnitude
  diagrams are compared with theoretical isochrones and color-magnitude
  diagrams of clusters with similar metallicity located further from
  the galactic center.

Title: The Current State of Solar Modeling
Authors: Christensen-Dalsgaard, J.; Dappen, W.; Ajukov, S. V.;
   Anderson, E. R.; Antia, H. M.; Basu, S.; Baturin, V. A.; Berthomieu,
   G.; Chaboyer, B.; Chitre, S. M.; Cox, A. N.; Demarque, P.; Donatowicz,
   J.; Dziembowski, W. A.; Gabriel, M.; Gough, D. O.; Guenther, D. B.;
   Guzik, J. A.; Harvey, J. W.; Hill, F.; Houdek, G.; Iglesias, C. A.;
   Kosovichev, A. G.; Leibacher, J. W.; Morel, P.; Proffitt, C. R.;
   Provost, J.; Reiter, J.; Rhodes, E. J., Jr.; Rogers, F. J.; Roxburgh,
   I. W.; Thompson, M. J.; Ulrich, R. K.
Bibcode: 1996Sci...272.1286C
Altcode:
  Data from the Global Oscillation Network Group (GONG) project and
  other helioseismic experiments provide a test for models of stellar
  interiors and for the thermodynamic and radiative properties, on which
  the models depend, of matter under the extreme conditions found in the
  sun. Current models are in agreement with the helioseismic inferences,
  which suggests, for example, that the disagreement between the predicted
  and observed fluxes of neutrinos from the sun is not caused by errors in
  the models. However, the GONG data reveal subtle errors in the models,
  such as an excess in sound speed just beneath the convection zone. These
  discrepancies indicate effects that have so far not been correctly
  accounted for; for example, it is plausible that the sound-speed
  differences reflect weak mixing in stellar interiors, of potential
  importance to the overall evolution of stars and ultimately to estimates
  of the age of the galaxy based on stellar evolution calculations.

Title: The Prospects for Asteroseismology from Ground-based Sites
Authors: Heasley, J. N.; Janes, Kenneth; Labonte, Barry; Guenther,
   David; Mickey, Donald; Demarque, Pierre
Bibcode: 1996PASP..108..385H
Altcode:
  We reexamine the possibility of detecting p-mode oscillations in
  Sun-like stars with ground-based telescopes. Previous attempts to
  make such observations with photometric techniques have been limited
  to subgiant stars in M67 and have illustrated the great difficulties
  involved in performing ground-based asteroseismology. Substantial gains
  in observing efficiency can be realized from new diagnostic techniques
  and improvements in instrumentation, especially with newer CCD camera
  systems. We show that for appropriately selected field stars observed
  with a network of telescopes or at a high duty cycle site, it will be
  possible to detect p-mode oscillations from the ground. An alternative
  to a network of telescopes for asteroseismology would be to develop a
  dedicated observatory for this purpose at a high duty cycle site, i.e.,
  the South Pole. We estimate the scintillation, the main noise source
  in asteroseismology, at the pole by modeling the index of refraction
  structure parameter from meterological data. The model results show that
  at the Pole the variance of the relative intensity fluctuations--i.e.,
  the scintillation--should be a factor of 5 smaller than at at Mauna
  Kea. Taking into account the improvements possible with target selection
  and instrumentation, the South Pole would be an excellent site for
  asteroseismological work on Sun-like stars. (SECTION: Stars)

Title: Seismology of the Standard Solar Model: Tests of Diffusion
    and the OPAL and MHD Equations of State
Authors: Guenther, D. B.; Kim, Y. -C.; Demarque, P.
Bibcode: 1996ApJ...463..382G
Altcode:
  The OPAL equation-of-state tables and the MHD equation-of-state tables
  are utilized in the calculation of new standard solar models that also
  include helium diffusion. The structure of the models and their l =
  0-100 p-mode oscillation spectra are compared. The p-mode frequencies
  of the standard solar model are dramatically and nearly identically
  affected by the inclusion of these detailed equation-of-state
  formulations. The sensitivities of the p-mode frequencies to other
  physical uncertainties, in particular the surface conditions, are
  also discussed.

Title: Testing Solar Models with the GONG Data
Authors: Christensen-Dalsgaard, J.; Dappen, W.; Demarque, P.; GONG
   Models Team
Bibcode: 1996AAS...188.5302C
Altcode: 1996BAAS...28..903C
  The wealth of very precise data from the GONG network and other
  helioseismic experiments provide a unique opportunity for testing the
  modeling of stellar interiors. Stellar modeling forms the basis for
  much of astrophysics. Furthermore, the application and calibration of
  solar models to the helioseismic data provides a test of the physics
  on which the models depend; thus we can investigate the thermodynamic
  and radiative properties of matter under the extreme conditions
  found in the Sun. Current models are in remarkable agreement with
  the helioseismic inferences within the errors in the input data; this
  suggests, for example, that the disagreement between the predicted and
  observed fluxes of neutrinos from the Sun is unlikely to be caused
  by errors in the standard solar model. However, careful analysis
  of the GONG data reveals subtle discrepancies that we attribute to
  uncertainties in some of the model input physics and the neglect of
  other subtle physical processes. The role of mixing inside the Sun,
  due for example to rotationally induced instabilities during its past
  evolution, the precise form of the hydrogen depletion profile near the
  center, the efficiency of helium and heavier element diffusion below
  the convection zone, and the structure of the highly superadiabatic
  layer just below the photosphere, are among the significant details in
  solar models, which the high-quality GONG data will greatly help to
  resolve. Comparisons between theoretical predictions of solar p-mode
  frequencies, previous p-mode observations and the first GONG data are
  used to illustrate these points.

Title: A Precision Age Determination Technique for Globular Clusters
Authors: Chaboyer, Brian; Demarque, Pierre; Kernan, Peter; Krauss,
   Lawrence M.; Sarajedini, Ata
Bibcode: 1996astro.ph..4122C
Altcode:
  Globular cluster age estimates based on the absolute magnitude of
  the main sequence turn-off (\mvto) are generally considered to be the
  most reliable from a theoretical viewpoint. However, the difficulty
  in determining \mvto\ in observed colour-magnitude diagrams leads
  to a large error in the derived age. In this paper, we advocate the
  use of the absolute magnitude of the point which is brighter than the
  turn-off and 0.05 mag redder (\mvb) as a precision age indicator. It
  is easy to measure this point on observed colour-magnitude diagrams,
  leading to small observational error bars. Furthermore, an extensive
  Monte Carlo calculation indicates that the theoretical uncertainty
  in \mvb\ is similar to \mvto. As a result, ages derived using \mvb\
  are at least a factor of 2 more precise than those derived using
  \mvto. This technique is applied to the globular cluster M68 and an
  age of $12.8\pm 0.3\,$Gyr is derived (assuming $\mvrr = 0.20\,\feh +
  0.98$), indicating that M68 is a `young' globular cluster. A homogeneous
  set of globular cluster age estimates with this precision would provide
  unprecedented insight into the formation of the Galactic halo.

Title: Modeling Convection in the Outer Layers of the Sun: A
    Comparison with Predictions of the Mixing-Length Approximation
Authors: Kim, Yong-Cheol; Fox, Peter A.; Demarque, Pierre; Sofia,
   Sabatino
Bibcode: 1996ApJ...461..499K
Altcode:
  The mixing-length theory (MLT) approximation (Vitense 1953) is used in
  most stellar evolution codes to describe the structure of the outer,
  highly superadiabatic, layers of the Sun. This procedure is known to be
  incorrect because of the MLT's inadequacies in describing convection and
  because of the need to include the strong coupling between radiation
  and convection in modeling this region. However, it is not known to
  what extent and precisely in what ways the MLT approximation distorts
  the structure of the highly superadiabatic peak in the outer convection
  zone. The purpose of this paper is to compare the statistical results
  of a more realistic three-dimensional numerical simulation of shallow
  convection to the predictions of the MLT. The simulations differ from
  the previous simulations of Chan &amp; Sofia (1989) in that they include
  a treatment of radiative transfer (in the diffusion approximation). The
  layers are super- adiabatic and exhibit a sharp peak in the temperature
  gradient. The results we derive from this simulation provide much more
  information than conventional one-dimensional theories of convective
  energy transport. We attempt to analyze or condense the information
  from the simulation to be compared with a traditional "theory" in
  an effort to establish how much a large eddy simulation can teach us
  about mean convective transport theories. In this paper we chose to
  use the mixing-length approximation for comparison. <P />The standard
  mixing-length approximation predicts a few linear relationships
  between local thermodynamic and dynamic quantities, the coefficients
  of which are functions of the mixing length. In these MLT relations,
  the ratio of mixing length to the local pressure scale is assumed to
  be constant over the entire convection zone, including the region
  of high superadiabaticity where convective energy transfer becomes
  less efficient.

Title: The Age of NGC 5927: Formation Timescales of the Halo and
    Thick Disk
Authors: Fullton, L. K.; Carney, B. W.; Olszewski, E. W.; Zinn, R.;
   Demarque, P.; Da Costa, G. S.; Janes, K. A.; Heasley, J. N.
Bibcode: 1996ASPC...92..269F
Altcode: 1996fogh.conf..269F
  We present the HST WFPC2 VI<SUB>C</SUB> color-magnitude diagram (CMD) of
  the metal-rich (thick) disk globular cluster NGC 5927. Our CMD indicates
  that NGC 5927 is somewhat younger than other disk globular clusters with
  known ages. Observations of the relative numbers of stars on the RGB and
  RHB indicate a large helium abundance, Y = +0.29+/-0.04. Comparison of
  the seven known thick disk globular clusters that have estimated ages
  with ages of globulars that belong to the halo reveals a significant
  overlap in age between the two cluster systems. As a group, the
  disk clusters appear somewhat younger than their halo counterparts,
  indicating that the Galactic halo began to form some 1--2 Gyr before
  the thick disk, in agreement with studies by Carney et al. (1990)
  and Marquez &amp; Schuster (1994).

Title: Globular Cluster Ages and the Formation of the Galactic Halo
Authors: Chaboyer, Brian; Demarque, P.; Sarajedini, Ata
Bibcode: 1996ApJ...459..558C
Altcode: 1995astro.ph..9063C
  Main-sequence turnoff magnitudes from the recent set of Yale isochrones
  published by Chaboyer et al. in 1995 have been combined with a variety
  of relations for the absolute magnitude of RR Lyrae stars [Mv(RR)]
  to calibrate age as a function of the difference in magnitude between
  the main-sequence turnoff and the horizontal branch (A VHToB). A best
  estimate for the calibration of Mv(RR) is derived from a survey of
  the current literature: Mv(RR) = 0.20[Fe/H] + 0.98. This estimate,
  together with other calibrations (with slopes ranging from 0.15 to
  0.30), has been used to derive A VTHoB ages for 43 Galactic globular
  clusters. Independent of the choice of Mv(RR), there is no strong
  evidence for an age- Galactocentric distance relationship among the
  43 globular clusters. However, an age-metallicity relation exists,
  with the metal-poor clusters being the oldest. A study of the age
  distribution reveals that an age range of 5 Gyr exists among the bulk
  of the globular clusters. In addition, about 10% of the sample are
  substantially younger, and including them in the analysis increases
  the age range to 9 Gyr. Once again, these statements are independent
  of the Mv(RR) relation. Evidence for age being the second parameter
  governing horizontal-branch morphology is found by comparing the average
  A VHToB age of the second parameter clusters to the normal clusters. The
  second parameter clusters are found to be on average 2-3 Gyr younger
  than the other clusters, which is consistent with age being the second
  parameter. These results suggest that globular clusters were formed
  over an extended period of time, with progressively more metal-rich
  globular clusters ([Fe/H] - 1.7) being formed at later times.

Title: A Lower Limit on the Age of the Universe
Authors: Chaboyer, Brian; Demarque, Pierre; Kernan, Peter J.; Krauss,
   Lawrence M.
Bibcode: 1996Sci...271..957C
Altcode: 1995astro.ph..9115C
  A detailed numerical study was designed and conducted to estimate the
  absolute age and the uncertainty in age (with confidence limits) of the
  oldest globular clusters in our galaxy, and hence to put a robust lower
  bound on the age of the universe. Estimates of the uncertainty range and
  distribution in the input parameters of stellar evolution codes were
  used to produce 1000 Monte Carlo realizations of stellar isochrones,
  which were then used to derive ages for the 17 oldest globular
  clusters. A probability distribution for the mean age of these systems
  was derived by incorporating the observational uncertainties in the
  measured color-magnitude diagrams for these systems and the predicted
  isochrones. The dominant contribution to the width of the distribution
  (approximately ±5 percent) resulted from the observational uncertainty
  in RR-Lyrae variable absolute magnitudes. Subdominant contributions
  came from the choice of the color table used to translate theoretical
  luminosities and temperatures to observed magnitudes and colors, as
  well as from theoretical uncertainties in heavy element abundances
  and mixing length. The one-sided 95 percent confidence limit lower
  bound for this distribution occurs at an age of 12.07 x 10^9 years,
  and the median age for the distribution is 14.56 x 10^9 years. These
  age limits, when compared with the Hubble age estimate, put powerful
  constraints on cosmology.

Title: Characteristic Temperature of UV Upturn of Elliptical Galaxies
Authors: Demarque, P.; Yi, S.; Oemler, A., Jr.
Bibcode: 1996ASPC...98..111D
Altcode: 1996fstg.conf..111D
  No abstract at ADS

Title: Are Blue Stragglers Mixed During Collisions?
Authors: Procter, A.; Bailyn, C. D.; Demarque, P.
Bibcode: 1996ASPC...90..380P
Altcode: 1996oedb.conf..380P
  No abstract at ADS

Title: Photometry of star clusters near the galactic center.
Authors: Heasley, J.; Janes, K.; Demarque, P.; Zinn, R.
Bibcode: 1996BAAS...28R.821H
Altcode:
  No abstract at ADS

Title: The Theoretical Calculation of the Rossby Number and the
    ``Nonlocal'' Convective Overturn Time for Pre-Main-Sequence and
    Early Post-Main-Sequence Stars
Authors: Kim, Yong-Cheol; Demarque, Pierre
Bibcode: 1996ApJ...457..340K
Altcode:
  This paper provides estimates of convective turnover timescales for
  Sun-like stars in the pre-main-sequence and early post-main-sequence
  phases of evolution, based on up-to-date physical input for the
  stellar models. In this first study, all models have solar abundances,
  which is typical of the stars in the Galactic disk, where most
  of the available data have been collected. A new feature of these
  models is the inclusion of rotation in the evolutionary sequences,
  thus making it possible to derive theoretically the Rossby number
  for each star along its evolutionary track, based on its calculated
  rotation rate and its local convective turnover time near the base of
  the convection zone. Global turnover times are also calculated for the
  complete convection zone. This information should make possible a new
  class of observational tests of stellar theory that were previously
  impossible with semiempirical models, particularly in the study of
  stellar activity and in research related to angular momentum transfer
  in stellar interiors during the course of stellar evolution.

Title: Seismology of η Bootis
Authors: Guenther, D. B.; Demarque, P.
Bibcode: 1996ApJ...456..798G
Altcode:
  The p-mode frequencies recently observed by Kjeldsen and coworkers,
  along with other observables, are used to determine the mass, age, and
  helium abundance of η Bootis. We show, by direct application, how the
  p-model frequencies and stellar seismological tools aid in constraining
  the physical parameters of η Boo. We confirm the existence of mode
  bumping and discuss how it may be used to refine the estimate of η
  Boo's age. We describe the effect of the new OPAL equation-of-state
  tables (Rogers, Swenson, and Iglesias) on the p-mode frequencies.

Title: Progress in helio- and astero-seismology
Authors: Demarque, P.; Guenther, D. B.
Bibcode: 1996ASPC..109...87D
Altcode: 1996csss....9...87D
  No abstract at ADS

Title: An answer to the UV upturn phenomenon of the elliptical
    galaxies?
Authors: Yi, Sukyoung; Demarque, P.; Oemler, A., Jr.
Bibcode: 1996ASPC...98..113Y
Altcode: 1996fstg.conf..113Y
  Recent discoveries about the UV upturn of the elliptical galaxies
  including (1) presence of the UV upturn in the old, metal-rich systems,
  (2) a positive correlation between the magnitude of the UV upturn
  and metallicity (Burstein et al. 1988), and (3) the characteristic
  temperature of the UV flux which is about 20000-23000 K (Brown et
  al. 1995), are consistent with the hypothesis that the hot HB stars are
  the main sources of the UV upturn. The UV upturn is governed mainly
  by age and metallicity which are key elements in understanding the
  formation and evolution of galaxies. Thus, exploiting the UV upturn
  phenomenon not only tells us about the hot stellar content in the
  galaxies but also provides important clues to cosmology. However,
  the UV flux is a complex function of age and metallicity. There are
  multiple solutions of age and metallicity that produce a similar
  amount of UV flux, but, whose implications for galaxy evolution are
  drastically different.

Title: Are Blue Stragglers Mixed during Collisions?
Authors: Procter Sills, Alison; Bailyn, Charles D.; Demarque, Pierre
Bibcode: 1995ApJ...455L.163P
Altcode: 1995ApJ...455L.163S
  The smoothed particle hydrodynamics (SPH) simulations of Benz &amp;
  Hills led to the assumption that blue stragglers created by collisions
  are initially fully mixed. The theoretical models of stars created
  under this assumption fit the observed blue straggler sequences
  well. Recently, however, Lombardi, Rasio, &amp; Shapiro performed SPH
  calculations of stellar collisions using a more realistic polytropic
  index for the structure of stars near the main-sequence turnoff. Their
  results show that the collision products are not mixed and, in fact,
  have composition profiles similar to those of the original stars. We
  have calculated evolutionary tracks for both the "unmixed" products
  and fully mixed products and have compared the results to the very
  bright blue stragglers in the center of NGC 6397. The unmixed stars
  are not as blue and not as bright as the observed stars, and they
  only live on the main sequence for a very short time. To account for
  the observed blue stragglers in NGC 6397, the collision products must
  either be more than twice the turnoff mass or mixed by some process
  subsequent to the initial collision and merger.

Title: Uncertainties in the Absolute Age of the Globular Clusters
Authors: Chaboyer, Brian; Kernan, Peter J.; Krauss, Lawrence M.;
   Demarque, Pierre
Bibcode: 1995AAS...187.0702C
Altcode: 1995BAAS...27.1292C
  As the longstanding discrepancy between the expansion age of the
  universe and the age of the oldest globular clusters continues,
  it becomes critically important to provide a realistic estimate of
  the error associated with the globular cluster age estimates. We
  report the results of a detailed numerical study designed to answer
  this question. Utilizing estimates of the uncertainty range (and
  distribution) in the input parameters of stellar evolution codes we
  produced 1000 Monte Carlo realizations of stellar isochrones, with
  which we could determine the ages of the 18 oldest globular clusters
  using the difference in magnitude between the main-sequence turnoff and
  the horizontal branch. Incorporating the observational uncertainties
  in the measured color-magnitude diagrams for these systems and the
  predicted isochrones, we derived a probability distribution for the mean
  age of these systems. Our best estimate is 14.6+/- 1.7 Gyr, with the
  one-sided 95% C.L. lower bound of 12.1 Gyr. The total error budget is
  dominated by the uncertainty in the absolute magnitude of the horizontal
  branch. Simply varying this quantity over its full 2sigma range, keeping
  all other parameters fixed, would produce a +/- 16% change in globular
  cluster ages estimates. Other significant input parameter uncertainties
  in this same sense are [alpha /Fe] (+/- 7 % effect), mixing length
  (+/- 5% effect), and diffusion, (14) Np reaction rate, the choice of
  colour table, and the primordial Helium abundance, each of which would
  affect age estimates at the +/-3% level if allowed to vary over its
  entire range, keeping all other parameters fixed. Simple formulae are
  provided which can be used to update our age estimate and its error
  as improved determinations for the above quantities become available.

Title: Horizontal Branch Morphology and the UV Upturn Phenomenon in
    the Elliptical Galaxies
Authors: Yi, S.; Demarque, P.; Oemler, A. A., Jr.
Bibcode: 1995AAS...187.8305Y
Altcode: 1995BAAS...27.1407Y
  Recent HUT observation of the FUV flux of several elliptical galaxies
  has been interpreted as due to the very low-mass, modestly metal-rich
  (about 1-2 solar), helium burning (horizontal branch - HB) stars,
  with a narrow range of temperature (Brown, Ferguson, &amp; Davidsen
  1995, ApJ, 454, L15). It is interesting to see if population synthesis
  models based purely on standard stellar evolution theory can explain
  these observational suggestions. The discovery of several analogous
  hot stars in the old, metal-rich open cluster NGC 6791 also suggests
  that higher mass loss rates should be considered for more metal-rich
  stars (Liebert, Saffer, &amp; Green, 1994, AJ, 107, 1408). We have
  constructed new helium burning phase evolutionary tracks using improved
  physics. Based on the tracks, synthetic HB models were built under the
  assumption of Delta Y/Delta Z=2 and 3 and a gaussian mass distribution
  on the HB with various mass loss efficiency parameters eta in the
  Reimers' formula. The mass distribution on the HB strongly affects the
  resulting composite UV spectra. We found that there is more than one
  solution which reproduces a similar magnitude of UV upturn. However,
  we prefer the modestly metal-rich populations with high mass loss
  rates as a solution because they can explain not only the magnitude
  of the UV flux but also strength of the absorption lines suggested by
  the HUT data, in a reasonable time scale (15-20 Gyr). Meanwhile, the
  physics which causes the unusually high mass loss for the metal-rich
  stars remains to be understood.

Title: Observational Tests for Ultraviolet Sources in Elliptical
    Galaxies
Authors: Yi, Sukyoung; Afshari, Ehsan; Demarque, Pierre; Oemler,
   Augustus, Jr.
Bibcode: 1995ApJ...453L..69Y
Altcode:
  An understanding of the empirical correlation between the strength
  of the UV upturn and the metallicity of luminous elliptical galaxies
  (Burstein and coworkers) is vital in the study of the evolution of
  elliptical galaxies. We support a modestly old (15--20 Gyr), metal-rich
  hypothesis ([Fe/H] &gt;~ 0) for the UV sources in UV upturn galaxies
  as an alternative to the old (&gt;~20 Gyr), metal-poor ([Fe/H] &lt;~
  -1.0) hypothesis of Park &amp; Lee. This preliminary result of our
  population synthesis is based on a Gaussian mass distribution on the
  horizontal branch and a complete library of stellar evolution tracks,
  both of which are crucial in producing UV light in the metal-rich
  systems. The metal-rich hypothesis has an advantage over the metal-poor
  one not only because it explains the UV upturn--metallicity relation
  but also because it requires neither an uncomfortably large age nor a
  large age span for elliptical galaxies. We suggest several observational
  tests to constrain the metallicity of the UV sources.

Title: Stellar Physics Using High-Resolution Spectroscopy with
    Large Telescopes
Authors: Demarque, Pierre
Bibcode: 1995PASP..107..994D
Altcode:
  The traditional high resolution domain of stellar physics will be
  profoundly affected by the deployment of 8-10 meter class telescopes. We
  discuss here some of the advances anticipated in the fields of stellar
  convection, seismology and magentic structures. Also discussed are
  the tests of stellar evolution and star formation processes that one
  may expect based on high resolution observations of radial velocity,
  Doppler imaging, and chemical abundances. (SECTION: Workshop on
  High-Resolution Spectroscopy)

Title: A VIC Color-Magnitude Diagram of the Globular Cluster NGC
    6352 From Hubble Space Telescope Planetary Camera Observations
Authors: Fullton, L. K.; Carney, B. W.; Olszewski, E. W.; Zinn, R.;
   Demarque, P.; Janes, K. A.; Da Costa, G. S.; Seitzer, P.
Bibcode: 1995AJ....110..652F
Altcode:
  The globular cluster NGC 6352, which on the basis of its Galactic
  position, radial velocity, and [Fe/H] is a member of the (thick)
  disk system of globular clusters, has been observed to below the
  main-sequence turnoff (MSTO) using the Hubble Space Telescope. These
  observations, which were obtained before the repair mission, were
  analyzed using the flux-conserving iterative/recursive deconvolution
  algorithm developed at the University of North Carolina. This algorithm
  can produce more precise photometry than standard PSF-fitting methods
  with the aberrated images. The V, (V-I<SUB>C</SUB>) color-magnitude
  diagram constructed from these observations places the cluster turnoff
  at V 18.80±0.10. Observations with the CTIO 0.9 m telescope have
  been used to photometer the brighter stars in the cluster, providing a
  calibration of the HST data and an estimate of the cluster's reddening,
  E(B-V) =0.21±0.03. From spectroscopic observations of the strengths of
  the Ca II triplet lines in red giants in the cluster and from previous
  measurements in the literature, we find that NGC 6352 is only slightly
  more metal rich (Δ[Fe/H]=0.08±0.05) than the prototypical disk
  globular cluster, 47 Tuc. From the difference in V magnitude between the
  horizontal branch and the MSTO, we find that NGC 6352 is essentially the
  same age as 47 Tuc (formally, older by 0.7±2.2 Gyr). Comparisons with
  the latest Yale isochrones support this result and yield 14.5±2 Gyr
  for the age of 47 Tuc from the photometry of Hesser et al. [PASP, 99,
  739 (1987)], which is consistent with other determinations. The old age
  obtained for NGC 6352 provides additional evidence that the disk system
  of globular clusters is very old and is in fact older or comparable
  in age to several globular clusters populating the Galactic halo.

Title: The theoretical calculation of the Rossby number and the
    `non-local' convective overturn time for pre-main sequence and early
    post-main sequence stars
Authors: -Cheol Kim, Yong; Demarque, Pierre
Bibcode: 1995astro.ph..7096.
Altcode: 1995astro.ph..7096K
  This paper provides estimates of convective turnover time scales
  for Sun-like stars in the pre-main sequence and early post-main
  sequence phases of evolution, based on up-to-date physical input
  for the stellar models. In this first study, all models have solar
  abundances, which is typical of the stars in the Galactic disk where
  most of the available data have been collected. A new feature of these
  models is the inclusion of rotation in the evolutionary sequences,
  thus making it possible to derive theoretically the Rossby number
  for each star along its evolutionary track, based on its calculated
  rotation rate and its local convective turnover time near the base of
  the convection zone. Global turnover times are also calculated for the
  complete convection zone. This information should make possible a new
  class of observational tests of stellar theory which were previously
  impossible with semi-empirical models, particularly in the study of
  stellar activity and in research related to angular momentum transfer
  in stellar interiors during the course of stellar evolution.

Title: Rotation, Diffusion, and Overshoot in the Sun: Effects on
    the Oscillation Frequencies and the Neutrino Flux
Authors: Chaboyer, Brian; Demarque, P.; Guenther, D. B.; Pinsonneault,
   M. H.
Bibcode: 1995ApJ...446..435C
Altcode: 1995astro.ph..1058C
  We have studied the importance of the combined effects of rotation,
  diffusion, and convective overshoot on the p-mode oscillation spectrum
  and the neutrino flux of the standard solar model. To isolate the
  various physical affects included in the new rotation plus diffusion
  models we also constructed solar models to test the significance of
  diffusion and of overshoot by themselves. In previous studies, models
  that include helium diffusion during solar evolution were found to
  improve the predicted p-mode frequencies for some modes and worsen the
  agreement for others (Guenther et al. 1993). Here we verify this result
  for both the Bahcall &amp; Loeb (1990) formulation of diffusion and the
  Proffitt &amp; Michaud (1991) formulation of diffusion. We find that
  the effects of rotation on the Sun's structure in the outer layers
  perturbs the p-mode frequencies only slightly when compared to the
  more substantial effects due to diffusion. In the thin overshoot layer
  (taken here to be 0.1 H<SUB>p</SUB>), we have compared the effect
  of over-mixing in a radiative layer versus convective (adiabatic)
  penetration. Neither radiative over-mixing nor adiabatic penetration
  has any significant effect on the p-modes, probably in part because the
  overshoot layer is constrained to be thin. The predicted neutrino flux
  in our diffusion plus rotation model is 7.12 SNU for Cl detectors, 127
  SNU for Ga detectors, and 5.00 × 10<SUP>6</SUP> ergs cm<SUP>-2</SUP>
  for the <SUP>8</SUP>B neutrinos; this is approximately half-way between
  the standard solar model without diffusion, and the standard solar
  model with diffusion alone.

Title: The Seismology of η Bootes
Authors: Demarque, P.; Guenther, D. B.
Bibcode: 1995ESASP.376b.555D
Altcode: 1995help.confP.555D; 1995soho....2..555D
  No abstract at ADS

Title: The Ages of the Disk Clusters NGC 188, M67, and NGC 752,
    Using Improved Opacities and Cluster Membership Data
Authors: Dinescu, Dana I.; Demarque, Pierre; Guenther, D. B.;
   Pinsonneault, M. H.
Bibcode: 1995AJ....109.2090D
Altcode:
  Theoretical isochrones have been constructed using the OPAL opacities
  to derive the ages of the open clusters NGC 188, M67, and NGC 752
  as well as to estimate the amount of convective overshoot at the
  convective core edge. We find that-under the assumptions made in the
  models-no overshoot, or a very small amount (up to 0.1 H<SUB>p</SUB>)
  is allowed for the best fits. Very good agreement is achieved between
  models and the main sequence, turnoff, subgiant, and giant branch for
  the clusters NGC 188 and M67. For NGC 188 and M67 we derive the ages:
  6.0<SUP>+1.0</SUP><SUB>-0.5</SUB> Gyr and 4.0±0.5 Gyr, respectively,
  where the main uncertainty is due to the estimate of the interstellar
  reddening. The age of NGC 752 is 2.0<SUP>+0.5</SUP><SUB>-0.3</SUB>
  Gyr if the adopted metallicity is [Fe/H] = - 0.27.

Title: Sensitivity of Solar g-Modes to Varying G Cosmologies
Authors: Guenther, D. B.; Sills, Ken; Demarque, Pierre; Krauss,
   Lawrence M.
Bibcode: 1995ApJ...445..148G
Altcode:
  The sensitivity of the solar g-mode oscillation spectrum to variability
  in the universal gravitational constant G is described. Solar models
  in varying G cosmologies were constructed by evolving a zero-age
  main-sequence stellar model to the Sun's current age, while allowing
  the value of G to change according to the power law G(t) proportional to
  t<SUP>-beta</SUP>, where Beta approximately equals delta G/GH and H is
  the Hubble constant. All solar models were constrained to the observed
  luminosity and radius at the current age of the Sun by adjusting the
  helium abundance and the mixing-length parameter of the models in
  the usual way for standard stellar models. Low-l g-mode oscillation
  periods were calculated for each of the models and compared to the
  claimed observation of the solar g-mode oscillation spectrum by Hill
  &amp; Gu (1990). If one accepts Hill &amp; Gu's claims, then within
  the uncertainties of the physics of the solar model calculation, our
  models rule out all but (delta G/GH) less than approximately 0.05. In
  other words, we conclude that G could not have varied by more than 2%
  over the past 4.5 Gyr, the lifetime of the present-day Sun. This result
  lends independent support to the validity of the standard solar model.

Title: Stellar Models with Microscopic Diffusion and Rotational
    Mixing. II. Application to Open Clusters
Authors: Chaboyer, B.; Demarque, P.; Pinsonneault, M. H.
Bibcode: 1995ApJ...441..876C
Altcode: 1994astro.ph..8059C
  Stellar models with masses ranging from 0.5 to $1.3~M_\odot$ were
  constructed in order to compare to young cluster observations of Li
  and of rotation velocities. The amount of Li depletion in cool stars
  is sensitive to the amount of overshoot at the base of the surface
  convection zone, and the exact metallicity of the models. Even when
  this uncertainty is taken into account, the Li observations are
  a severe constraint for the models and rule out standard models,
  and pure diffusion models. Stellar models which include diffusion
  and rotational mixing in the radiative regions of stars are able
  to simultaneously match the Li abundances observed in the Pleiades,
  UMaG, Hyades, Praesepe, NGC 752 and M67. They also match the observed
  rotation periods in the Hyades. However, these models are unable to
  simultaneously explain the presence of the rapidly rotating late G
  and K stars in the Pleiades and the absence of rapidly rotating late
  F and early G stars.

Title: Modeling of Shallow and Inefficient Convection in the Outer
    Layers of the Sun Using Realistic Physics
Authors: Kim, Yong-Cheol; Fox, Peter A.; Sofia, Sabatino; Demarque,
   Pierre
Bibcode: 1995ApJ...442..422K
Altcode:
  In an attempt to understand the properties of convective energy
  transport in the solar convective zone, a numerical model has been
  constructed for turbulent flows in a compressible, radiation-coupled,
  nonmagnetic, gravitationally stratified medium using a realistic
  equation of state and realistic opacities. The time-dependent,
  three-dimensional hydrodynamic equations are solved with minimal
  simplifications. The statistical information obtained from the present
  simulation provides an improved understanding of solar photospheric
  convection. The characteristics of solar convection in shallow regions
  is parameterized and compared with the results of Chan &amp; Sofia's
  (1989) simulations of deep and efficient convection. We assess the
  importance of the zones of partial ionization in the simulation and
  confirm that the radiative energy transfer is negligible throughout
  the region except in the uppermost scale heights of the convection
  zone, a region of very high superadiabaticity. When the effects of
  partial ionization are included, the dynamics of flows are altered
  significantly. However, we confirm the Chan &amp; Sofia result that
  kinetic energy flux is nonnegligible and can have a negative value in
  the convection zone.

Title: Theoretical Color Calibration for HST FOC Ultraviolet Filters
Authors: Yi, Sukyoung; Demarque, Pierre; Oemler, Augustus, Jr.
Bibcode: 1995PASP..107..273Y
Altcode:
  A theoretical color calibration is carried out for three (F140W,
  F220W, and F342W) of the most heavily used ultraviolet filters,
  and one visual band filter (F480LP) in the Faint Object Camera on
  the HST, using the new Kurucz model spectra which became available
  recently. It is known that the UV filters suffer from the visible
  leak problem, and it is apparent in this study that the visible leak
  problem can cause serious trouble to analyses of observed data. We
  show here that some of the colors defined from these filters do not
  have a monotonic relation with effective temperature; and thus, the
  colors fail to indicate a unique effective temperature in certain
  temperature ranges. This study shows that the problem can be solved
  by using one of the visual band filters, preferably F480LP, together
  with the UV filters. The expected model color-magnitude diagrams for
  a typical globular cluster with the HST ultraviolet colors are also
  provided. (SECTION: Astronomical Instrumentation)

Title: Stellar Models with Microscopic Diffusion and Rotational
    Mixing. I. Application to the Sun
Authors: Chaboyer, Brian; Demarque, P.; Pinsonneault, M. H.
Bibcode: 1995ApJ...441..865C
Altcode: 1994astro.ph..8058C
  The Yale stellar evolution code has been modified to include the
  combined effects of diffusion and rotational mixing on $^1$H, $^4$He and
  the trace elements $^3$He, $^6$Li, $^7$Li, and $^9$Be. The interaction
  between rotational mixing and diffusion is studied by calculating a
  number of calibrated solar models. The rotational mixing inhibits the
  diffusion in the outer parts of the models, leading to a decrease in
  the envelope diffusion by 25 -- 50\%. Conversely, diffusion leads to
  gradients in mean molecular weight which can inhibit the rotational
  mixing. The degree to which gradients in mean molecular weight
  inhibits the rotational mixing is somewhat uncertain. A comparison
  to the observed solar oblateness suggests that gradients in the mean
  molecular weight play a smaller role in inhibiting the rotational mixing
  previously believed. This is reinforced by the fact that the model with
  the standard value for the inhibiting effect of mean molecular weight
  on the rotational mixing depletes no Li on the main sequence. This is
  in clear contrast to the observations. A reduction in the inhibiting
  effect of mean molecular weight gradients by a factor of ten leads to
  noticeable main sequence Li depletion.

Title: Main Sequence and H-Shell Burning: Convection and Seismology
Authors: Demarque, P.; Guenther, D. B.; Kim, Y. -C.
Bibcode: 1995LIACo..32..279D
Altcode: 1995sews.book..279D
  No abstract at ADS

Title: Modeling Convection in the Outer Layers of the Sun : Constancy
    of the Mixing Length Ratio near the Top of Convection Zone
Authors: Kim, Y. -C.; Fox, P. A.; Demarque, P.; Sofia, S.
Bibcode: 1995LIACo..32..195K
Altcode: 1995sews.book..195K
  The purpose of this poster is to utilize the results of a numerical
  simulation of solar convection based on a physically realistic
  description of the shallow layers, and to compare the results with one
  of the basic assumption of the standard mixing length approximation,
  namely, a constant mixing length ratio throughout a convection zone.

Title: Ages of galactic globular clusters from the new Yale
    isochrones.
Authors: Chaboyer, B.; Demarque, P.; Guenther, D. B.; Pinsonneault,
   M. H.; Pinsonneault, L. L.
Bibcode: 1995fmw..conf..289C
Altcode: 1994astro.ph.11024C
  A new grid of theoretical isochrones based on the Yale stellar evolution
  code using the OPAL and Kurucz opacities has been constructed. The grid
  of isochrones spans a wide range of metallicities, helium abundances
  and masses. The construction of the isochrones is described and the
  isochrones are compared to galactic globular cluster observations. A
  solar calibrated mixing length (α = 1.7) yields a good fit to globular
  cluster colour-magnitude diagrams. Ages for 40 globular clusters are
  determined using the ΔV(TO-HB) method and the formation of the halo
  is discussed.

Title: Concluding Remarks
Authors: Demarque, P.
Bibcode: 1995LIACo..32..489D
Altcode: 1995sews.book..489D
  No abstract at ADS

Title: Stellar evolution: what should be done
Authors: Noels, A.; Fraipont-Caro, D.; Gabriel, M.; Grevesse, N.;
   Demarque, P.
Bibcode: 1995sews.book.....N
Altcode:
  No abstract at ADS

Title: The Combined Effects of Rotation and Diffusion on the Standard
    Solar Model
Authors: Demarque, P.; et al.
Bibcode: 1995somo.conf..151D
Altcode:
  No abstract at ADS

Title: Helioseismology
Authors: Demarque, P.; Chaboyer, B.; Guenther, D. B.; Pinsonneault,
   M. H.
Bibcode: 1995ASPC...78..417D
Altcode: 1995aapn.conf..417D
  No abstract at ADS

Title: Helioseismology, solar evolution and other physics
Authors: Demarque, P.; Chaboyer, B.; Guenther, D. B.; Pinsonneault,
   M. H.
Bibcode: 1995HiA....10..332D
Altcode:
  No abstract at ADS

Title: The Sun as a Probe of Varying G
Authors: Demarque, P.; Krauss, Lawrence M.; Guenther, D. B.; Nydam,
   David
Bibcode: 1994ApJ...437..870D
Altcode:
  In order to explore the ability of helioseismology and features of
  solar models to test the constancy of the gravitational constant G
  during the last 4.5 Gyr of solar evolution, we have constructed a grid
  of evolutionary sequences for solar models under the assumptions that G
  varies with time, and have explored the sensitivity of their nonradial
  acoustic mode oscillation spectra to G variability. All final models
  satisfy the standard constraints for the present Sun and, except for the
  variation in G, were constructed under the assumptions of a standard
  solar model. When compared with the observed solar p-mode spectrum,
  our models definitely rule out beta greater than 0.4 and beta less
  than -0.4, where G(t) proportional to t<SUP>-beta</SUP> over the last
  4.5 Gyr. These limits can be tightened to rule out absolute value of
  beta greater than 0 (0.1) by the use of other solar observables. For
  nonmonotonic variation in G this suggests that long-timescale variations
  greater than 0 (5%) in G are ruled out over the last 4.5 Gyr. Future
  prospects for improving the sensitivity of helioseismic tests of a
  varying G are also discussed. Finally, we explore the sensitivity of
  the predicted solar neutrino flux to varying G.

Title: Theoretical Color Calibration for HST FOC Ultraviolet Filters
Authors: Yi, Sukyoung; Demarque, Pierre; Oemler, Augustus, Jr.
Bibcode: 1994AAS...185.0910Y
Altcode: 1994BAAS...26.1320Y
  Theoretical color calibration is carried out for three (F140W, F220W,
  and F342W) of the most heavily used ultraviolet filters and one visual
  band filter (F480LP) in the Faint Object Camera on the HST, using the
  new Kurucz model spectra which became available recently. It is known
  that the UV filters suffer from the visible leak problem, and it is
  apparent in this study that the visible leak problem can cause serious
  trouble to analyses of observed data. We show here that some of the
  colors defined from these filters do not have a monotonic relation with
  effective temperature; and thus, the colors fail to indicate a single
  effective temperature in certain temperature ranges. This study shows
  that the problem can be solved by using one of the visual band filters,
  preferably F480LP, together with the UV filters. The expected model
  color-magnitude diagrams for a typical globular cluster with the HST
  ultraviolet colors are also provided.

Title: 7Li Abundances in Halo Stars: Testing Stellar Evolution Models
    and the Primordial 7Li Abundance
Authors: Chaboyer, Brian; Demarque, P.
Bibcode: 1994ApJ...433..510C
Altcode: 1994astro.ph..3043C
  A large number of stellar evolution models with [Fe/H] = -2.3 and
  -3.3 have been calculated in order to determine the primordial $^7$Li
  abundance and to test current stellar evolution models by a comparison
  to the extensive database of Li abundances in extremely metal poor
  halo stars observed by Thorburn (1994). Standard models do a good
  job of fitting the observed Li abundances in stars hotter than 5600
  K. They predict a primordial $^7$Li abundance of Log N(Li) = 2.24\pm
  0.03$. Models which include microscopic diffusion predict a downward
  curvature in the $^7$Li destruction isochrones at hot temperatures which
  is not present in the observations. Thus, the observations clearly rule
  out models which include uninhibited microscopic diffusion of $^7$Li
  from the surface of the star. The [Fe/H] = -2.3 stellar models which
  include both diffusion and rotational mixing provide an excellent match
  to the observations. Both the plateau stars and the heavily depleted
  cool stars are well fit by these models. The rotational mixing leads to
  considerable $^7$Li depletion in these models and the primordial $^7$Li
  abundance inferred from these models is Log N(Li) = $3.08\pm 0.1$.

Title: The Gap in the Color-Magnitude Diagram of NGC 2420: A Test
    of Convective Overshoot and Cluster Age
Authors: Demarque, Pierre; Sarajedini, Ata; Guo, X. -J.
Bibcode: 1994ApJ...426..165D
Altcode:
  Theoretical isochrones have been constructed using the OPAL opacities
  specifically to study the color-magnitude diagram of the open star
  cluster NGC 2420. This cluster provides a rare test of core convection
  in intermediate-mass stars. At the same time, its age is of interest
  because of its low metallicity and relatively high Galactic latitude for
  an open cluster. The excellent color-magnitude diagram constructed by
  Anthony-Twarog et al. (1990) allows a detailed fit of the isochrones
  to the photometric data. We discuss the importance of convective
  overshoot at the convective core edge in determining the morphology
  of the gap located near the main-sequence turnoff. We find that given
  the assumptions made in the models, a modest amount of overshoot
  (0.23 H<SUB>p</SUB>) is required for the best fit. Good agreement is
  achieved with all features of the turnoff gap for a cluster age of
  2.4 +/- 0.2 Gyr. We note that a photometrically complete luminosity
  function near the main-sequence turnoff and subgiant branch would also
  provide an important test of the overshoot models.

Title: Modelling of Shallow and Inefficient Convection in the Outer
    Layers of the Sun Using Realistic Physics
Authors: -Cheol Kim, Yong; Fox, Peter A.; Sofia, Sabatino; Demarque,
   Pierre
Bibcode: 1994astro.ph..3046.
Altcode: 1994astro.ph..3046K
  In an attempt to understand the properties of convective energy
  transport in the solar convection zone, a numerical model has been
  constructed for turbulent flows in a compressible, radiation-coupled,
  non-magnetic, gravitationally stratified medium using a realistic
  equation of state and realistic opacities. The time-dependent,
  three-dimensional hydrodynamic equations are solved with minimal
  simplifications. The statistical information obtained from the present
  simulation provides an improved understanding of solar photospheric
  convection. The characteristics of solar convection in shallow
  regions is parameterized and compared with the results of Chan and
  Sofia's simulations of deep and efficient convection (Chan and Sofia
  1989). We assess the importance of the zones of partial ionization
  in the simulation, and confirm that the radiative energy transfer is
  negligible throughout the region except in the uppermost scale heights
  of the convection zone, a region of very high super-adiabaticity. When
  the effects of partial ionization are included, the dynamics of flows
  are altered significantly. However, we confirm the Chan and Sofia
  result that kinetic energy flux is non-negligible and can have a
  negative value in the convection zone.

Title: Mass Loss during the RR Lyrae Phase of the Horizontal Branch:
    Mass Dispersion on the Horizontal Branch and RR Lyrae Period Changes
Authors: Koopmann, Rebecca A.; Lee, Young-Wook; Demarque, Pierre;
   Howard, Jamie M.
Bibcode: 1994ApJ...423..380K
Altcode:
  Mass loss on the horizontal branch has been invoked in the literature
  to explain such phenomena as the color (mass) dispersion of the
  horizontal branch and the observed distribution of period changes
  in RR Lyrae stars. To test these claims, the Yale stellar evolution
  code was used to evolve horizontal branch models of masses 0.64, 0.66,
  0.68, 0.70, and 0.72 solar mass with Z of 0.001, core mass of 0.4893,
  main-sequence helium abundance of 0.23, and constant mass loss rates
  of 0, 10<SUP>-10</SUP>, 5 x 10<SUP>-10</SUP>, and 10<SUP>-9</SUP>
  solar mass/yr. Mass loss was assumed to occur only in the instability
  strip, where a mechanism is most likely to exist. Synthetic horizontal
  branches, constructed from the models, show that mass loss on the
  horizontal branch cannot produce the observed color dispersion even
  for the highest mass-loss rate of 10<SUP>-9</SUP> solar mass/yr. Mass
  loss is unlikely to occur at a higher rate without significant
  effects on the horizontal branch morphology, which would destroy the
  good agreement between standard synthetic models without mass loss
  and observed horizontal branches. Periods and period changes were
  calculated for all models. The period changes are not significantly
  larger for models with mass loss. The effect of mass loss in clusters
  of other metallicities is discussed.

Title: The Horizontal-Branch Stars in Globular Clusters. II. The
    Second Parameter Phenomenon
Authors: Lee, Young-Wook; Demarque, Pierre; Zinn, Robert
Bibcode: 1994ApJ...423..248L
Altcode:
  Using synthetic horizontal-branch models, we have investigated
  the origin of the systematic variation in horizontal-branch (HB)
  morphology with galactocentric distance (R<SUB>G</SUB>) among globular
  clusters. The variations in He abundance, CNO abundance, and core
  mass required separately to explain this effect are inconsistent
  with either the observed properties of the RR Lyrae variables or the
  observed main-sequence turnoffs in the clusters. There is also no
  clear evidence that the trend with R<SUB>G</SUB> is related to the
  central concentrations, central densities, or absolute magnitudes
  of the clusters. The variations in cluster age required to explain
  this effect are not in conflict with any observations. A detailed
  comparison of our synthetic HB calculations with pairs of clusters
  of very different HB morphology but similar (Fe/H) reveals reasonably
  good agreement between the age differences inferred from HB morphology
  and the main-sequence turnoff. The major source of uncertainty is the
  need for ad hoc hypotheses in the modeling of the HB morphologies
  of a few peculiar clusters (e.g., NGC 6752). Nonetheless, there is
  firm evidence for age variations of several gigayears (as much as
  approximately 5 Gyr) among the halo globular clusters. Our results
  support the hypothesis of Searle &amp; Zinn that the inner halo is
  more uniform in age and is older in the mean than the outer halo,
  and we estimate this difference to be approximately 2 Gyr.

Title: Report of IAU Commission 35: Stellar constitution (Constitution
    des étoiles).
Authors: Demarque, P.
Bibcode: 1994IAUTA..22..399D
Altcode:
  No abstract at ADS

Title: The Evolution of Rotating 15 M solar Stars
Authors: Sofia, S.; Howard, J. M.; Demarque, P.
Bibcode: 1994IAUS..162..131S
Altcode:
  No abstract at ADS

Title: The Extended Horizontal-Branch: A Challenge for Stellar
    Evolution Theory
Authors: Demarque, Pierre
Bibcode: 1994hsgh.conf..362D
Altcode:
  No abstract at ADS

Title: Diffusion and Rotational Mixing in Stellar Models
Authors: Chaboyer, Brian; Demarque, P.
Bibcode: 1994ASPC...64..273C
Altcode: 1994csss....8..273C
  No abstract at ADS

Title: The Effect of Livermore Opal Opacities on the Evolutionary
    Masses of RR Lyrae Stars
Authors: Yi, Sukyoung; Lee, Young-Wook; Demarque, Pierre
Bibcode: 1993ApJ...411L..25Y
Altcode:
  We have investigated the effect of the new Livermore OPAL opacities
  on the evolution of horizontal-branch (HB) stars. This work was
  motivated by the recent stellar pulsation calculations using the new
  Livermore opacities, which suggest that the masses of double-mode RR
  Lyrae stars are 0.1-0.2 solar mass larger than those based on earlier
  opacities. Unlike the pulsation calculations, we find that the effect
  of opacity change on the evolution of HB stars is not significant. In
  particular, the effect of the mean masses of RR Lyrae stars is very
  small, showing a decrease of only 0.01-0.02 solar mass compared to
  the models based on old Cox-Stewart opacities. Consequently, with
  the new Livermore OPAL opacities, both the stellar pulsation and
  evolution models now predict approximately the same masses for the RR
  Lyrae stars. Our evolutionary models suggest that the mean masses of
  the RR Lyrae stars are about 0.76 and about 0.71 solar mass for M15
  (Oosterhoff group II) and M3 (group I), respectively. If (alpha/Fe) =
  0.4, these values are decreased by about 0.03 solar mass. Variations
  of the mean masses of RR Lyrae stars with HB morphology and metallicity
  are also presented.

Title: Evolution and Seismology of Procyon
Authors: Guenther, D. B.; Demarque, P.
Bibcode: 1993ApJ...405..298G
Altcode:
  We have calculated an array of stellar models for Procyon A that
  are based on the best physics available to us, including the latest
  opacities and nuclear cross sections. The array of models spans
  the error space centered on Procyon's mass, chemical composition,
  effective temperature, and luminosity. We find that with OPAL opacities
  no convective overshoot is needed at the edge of the convective core to
  match Procyon's position in the H-R diagram. We discuss the discrepancy
  between the astrophysical mass and the astrometric mass, which is
  reduced by the more up-to-date physics in the models, and describe
  how oscillation data can be used to distinguish among the possible
  models and help resolve the discrepancy. We have calculated oscillation
  frequencies for the l = 0, 1, 2, and 3 p-modes and oscillation periods
  for the l = 1, 2, and 3 g-modes for several of these models.

Title: Seismology of Procyon
Authors: Guenther, D. B.; Demarque, P.
Bibcode: 1993ASPC...42..379G
Altcode: 1993gong.conf..379G
  No abstract at ADS

Title: New Physics, New Isochrones
Authors: Demarque, P.; Guenther, D. B.; Pinsonneault, M. H.; Cheboyer,
   B.; Yi, S.
Bibcode: 1993ASPC...48..191D
Altcode: 1993gcgc.work..191D
  No abstract at ADS

Title: Key issues - A round table discussion
Authors: Brown, T. M.; Demarque, P.; Noyes, R.; Praderie, F.; Roxburgh,
   I. W.; Schatzman, E.
Bibcode: 1993ASPC...40..776B
Altcode: 1993ist..proc..776B; 1993IAUCo.137..776B
  An overview of a round table discussion on the internal dynamics of
  stars, some problems in stellar structure and evolution, a study of
  stellar activity mechanisms using PRISMA, the seismology of sunlike
  stars, and directions of future research is presented. It is concluded
  that models that take into account just one physical process generally
  do not agree with the observations. This provides evidence for the
  presence of other physical processes. In each phenomenon which is
  considered, a variety of physical processes are involved. All physical
  processes should be taken into account simultaneously. Stars need to
  be considered globally. It is recommended that attention be given to
  such unsolved problems as the helium content of the sun, the abundance
  of lithium in fast rotating stars, and the origin and evolution of
  stellar magnetic fields.

Title: New physics, new evolutionary tracks, new isochrones
Authors: Demarque, P.; Guenther, D. B.; Pinsonneault, B.
Bibcode: 1993ASPC...40..448D
Altcode: 1993IAUCo.137..448D; 1993ist..proc..448D
  No abstract at ADS

Title: Effects of Microscopic Diffusion and Rotational Mixing on
    Stellar Models
Authors: Chaboyer, Brian; Demarque, P.; Pinsonneault, M. H.
Bibcode: 1992AAS...181.3609C
Altcode: 1992BAAS...24.1176C
  Microscopic diffusion of the trace elements He3, Li7 and Be9 have been
  incorporated into the rotating stellar evolution code at Yale. The
  consequences of diffusion and rotational mixing are investigated for
  solar models and young cluster stars. The inhibition of diffusion
  due to rotational mixing (and vice versa) is explored. A comparison
  is made to abundance measurements of Li7 and rotational velocities in
  the Sun and young cluster stars. This work was partially supported by
  NASA grants NAG5--1486 and NAGW--2531.

Title: The metal-rich globular cluster NGC 6553: clump morphology
    and age.
Authors: Demarque, P.; Lee, Y. -W.
Bibcode: 1992A&A...265...40D
Altcode:
  Stellar evolutionary tracks for metal-rich HB stars have been used
  to construct synthetic population models for the peculiar HB clump
  in NGC 6553. Although the uncertainties are large, it is possible to
  derive an age for NGC 6553 in the range 8-13 Gyr, which supports the
  idea that the disk globular cluster system is younger than the oldest
  stars in the Galactic halo and bulge.

Title: Stellar Photospheric Convection, and the Effect on Spectral
    Line Asymmetry
Authors: Kim, Y. -C.; Demarque, P.; Fox, P. A.
Bibcode: 1992AAS...181.3605K
Altcode: 1992BAAS...24.1175K
  No abstract at ADS

Title: Ages of Globular Clusters and Helium Diffusion
Authors: Chaboyer, Brian; Sarajedini, Ata; Demarque, Pierre
Bibcode: 1992ApJ...394..515C
Altcode:
  Evolutionary tracks have been calculated with alpha-enhanced
  compositions which cover the entire globular cluster metallicity
  range and have constructed isochrones which include the effects
  of microscopic diffusion of helium. The turnoff magnitudes from the
  isochrones were combined with the theoretical RR Lyrae magnitudes from
  Lee to determine the ages of 32 Galactic globular clusters using the
  magnitude difference between the turnoff and horizontal branch. It is
  found that including the effects of helium diffusion has a negligible
  effect on the derived ages of globular clusters. Regardless of the
  inclusion of helium diffusion, a significant age spread of 5 Gyr among
  the globular clusters is found. The oldest globular clusters studied
  here are 17 +/- 2 Gyr old.

Title: Evolutionary Models and the p-Mode Oscillation Spectrum of
    alpha Centauri A and B
Authors: Edmonds, Peter; Cram, Lawrence; Demarque, Pierre; Guenther,
   D. B.; Pinsonneault, Marc H.
Bibcode: 1992ApJ...394..313E
Altcode:
  Spectroscopically observed abundances of Furenlid and Meylan (1990) and
  Los Alamos Opacity Library opacities specifically constructed for this
  mixture are used to construct the most detailed models to date for Alpha
  Cen A and B. Models including the effects of the diffusion of helium in
  Alpha Cen A's interior were constructed. Although the effect of helium
  diffusion is small in Alpha Cen A, it is slightly larger than in the
  sun because of the larger mass and therefore shallower convection zone
  of Alpha Cen A. Keeping the heavy-element mixture unchanged but varying
  Z within the uncertainties yields limits to the helium abundance of Y
  = 0.295 and 0.305, respectively. The derived age of Alpha Cen is 4.6
  +/-0.4 Gyr, very similar to the solar age of 4.5 Gyr.

Title: Standard Solar Model. II. g-Modes
Authors: Guenther, D. B.; Demarque, P.; Pinsonneault, M. H.; Kim,
   Y. -C.
Bibcode: 1992ApJ...392..328G
Altcode:
  The paper presents the g-mode oscillation for a set of modern
  solar models. Each solar model is based on a single modification or
  improvement to the physics of a reference solar model. Improvements
  were made to the nuclear reaction rates, the equation of state,
  the opacities, and the treatment of the atmosphere. The error in the
  predicted g-mode periods associated with the uncertainties in the model
  physics is predicted and the specific sensitivities of the g-mode
  periods and their period spacings to the different model structures
  are described. In addition, these models are compared to a sample of
  published observations. A remarkably good agreement is found between
  the 'best' solar model and the observations of Hill and Gu (1990).

Title: The Effect of Helium Diffusion on the Ages of Globular Clusters
Authors: Chaboyer, Brian; Deliyannis, Constantine P.; Demarque,
   Pierre; Pinsonneault, M. H.; Sarajedini, Ata
Bibcode: 1992ApJ...388..372C
Altcode:
  Evolutionary tracks for halo stars were calculated, and isochrones
  which include the effects of microscopic diffusion of helium were
  constructed. The isochrones were fitted to a metal poor (M92) and
  a moderately metal rich (NGC 288) globular cluster using an updated
  version of the Revised Yale Isochrone color calibration. Ages of the two
  clusters were also determined using the difference between the turnoff
  magnitude and horizontal branch magnitude, and the difference in color
  between the main-sequence turnoff and lower giant branch. Considering
  all methods and constraints, diffusion is argued to reduce the derived
  ages of M92 and NGC 288 by 0.5-1 Gyr. The maximum age reduction that
  diffusion could cause is 3 Gyr. Age estimates including diffusion
  indicate that M92 is 16 +/- 2 Gyr old, and that M92 is about 3 Gyr older
  than NGC 288, assuming that the clusters have the same O/Fe of +0.4.

Title: The Evolution of High-Metallicity Horizontal-Branch Stars
    and the Origin of the Ultraviolet Light in Elliptical Galaxies
Authors: Horch, E.; Demarque, P.; Pinsonneault, M.
Bibcode: 1992ApJ...388L..53H
Altcode:
  Evolutionary calculations of high-metallicity horizontal-branch
  stars show that for the relevant masses and helium abundances,
  post-HB evolution in the HR diagram does not proceed toward and along
  the AGB, but rather toward a "slow blue phase" in the vicinity of
  the helium- burning main sequence, following the extinction of the
  hydrogen shell energy source. For solar and twice solar metallicity,
  the blue phase begins during the helium shell-burning phase (in
  agreement with the work of Brocato and Castellani &amp; Tornambe);
  for 3 times solar metallicity, it begins earlier, during the helium
  core-burning phase. This behavior differs from what takes place at
  lower metallicities. The implications for high-metallicity old stellar
  populations in the Galactic bulge and for the integrated colors of
  elliptical galaxies are discussed.

Title: Standard Solar Model
Authors: Guenther, D. B.; Demarque, P.; Kim, Y. -C.; Pinsonneault,
   M. H.
Bibcode: 1992ApJ...387..372G
Altcode:
  A set of solar models have been constructed, each based on a single
  modification to the physics of a reference solar model. In addition,
  a model combining several of the improvements has been calculated to
  provide a best solar model. Improvements were made to the nuclear
  reaction rates, the equation of state, the opacities, and the
  treatment of the atmosphere. The impact on both the structure and the
  frequencies of the low-l p-modes of the model to these improvements
  are discussed. It is found that the combined solar model, which is
  based on the best physics available (and does not contain any ad hoc
  assumptions), reproduces the observed oscillation spectrum (for low-l)
  within the errors associated with the uncertainties in the model physics
  (primarily opacities).

Title: Solar Calibration and the Age of the Old Disk Clusters M67,
    NGC 188, and NGC 6791
Authors: Demarque, Pierre; Green, E. M.; Guenther, D. B.
Bibcode: 1992AJ....103..151D
Altcode:
  The ages of the old disk star clusters M67, NGC 188, and NGC
  6791 are derived on the basis of theoretical solar calibrated
  isochrones. The ages of M67 and NGC 188 were found to be about 4.0
  +1.0 or -0.5 Gyr (close to the age of the sun) and 6.5 +1.5 or -0.5
  Gyr, respectively. The age of NGC 6791 was found to be about 1.0 Gyr
  larger than that of NGC 188, assuming that the two clusters have the
  same metallicity. If, however, NGC 6791 is more metal rich, its age
  is less certain; it could be as low as 6.5 Gyr.

Title: Evolutionary Models of Halo Stars with Rotation. II. Effects
    of Metallicity on Lithium Depletion, and Possible Implications for
    the Primordial Lithium Abundance
Authors: Pinsonneault, M. H.; Deliyannis, Constantine P.; Demarque, P.
Bibcode: 1992ApJS...78..179P
Altcode: 1992ApJS...78...79P
  Models of metal-poor stars with rotation were computed and their
  lithium depletion was compared with observations of halo stars. The
  models that have turn-off ages compatible with the observations have a
  nearly flat Li-T(eff) relationship in the region of the Spite lithium
  'plateau'. Depending on the initial angular momentum, the models have
  a depletion factor ranging between a factor of 5 and a factor of 10 at
  fixed T(eff), implying a maximum initial lithium abundance of 3.1. Both
  the dispersion and the overall depletion factor are much smaller for
  metal-poor models than for solar metallicity ones. The factors that
  determine lithium depletion in rotational models are discussed and
  the different depletion patterns in solar metallicity and metal-poor
  models are traced to differences in their structure and evolution. The
  dependence of the lithium depletion on age, mass, initial angular
  momentum, and metallicity is also discussed. The dispersion predicted
  from these models is not inconsistent with the observations.

Title: The Effect of the Mihalas, Hummer, and Daeppen Equation of
    State and the Molecular Opacity on the Standard Solar Model
Authors: Kim, Y. -C.; Demarque, P.; Guenther, D. B.
Bibcode: 1991ApJ...378..407K
Altcode:
  Improvements to the Yale Rotating Stellar Evolution Code (YREC)
  by incorporating the Mihalas-Hummer-Daeppen equation of state, an
  improved opacity interpolation routine, and the effects of molecular
  opacities, calculated at Los Alamos, have been made. the effect of
  each of the improvements on the standard solar model has been tested
  independently by computing the corresponding solar nonradial oscillation
  frequencies. According to these tests, the Mihalas-Hummer-Daeppen
  equation of state has very little effect on the model's low l p-mode
  oscillation spectrum compared to the model using the existing analytical
  equation of state implemented in YREC. On the other hand, the molecular
  opacity does improve the model's oscillation spectrum. The effect
  of molecular opacity on the computed solar oscillation frequencies
  is much larger than that of the Mihalas-Hummer-Daeppen equation
  of state. together, the two improvements to the physics reduce the
  discrepancy with observations by 10 microHz for the low l modes.

Title: Lithium in Halo Stars: Constraining the Effects of Helium
    Diffusion on Globular Cluster Ages and Cosmology
Authors: Deliyannis, Constantine P.; Demarque, Pierre
Bibcode: 1991ApJ...379..216D
Altcode:
  Stellar evolutionary models with diffusion are used to show that
  observations of lithium in extreme halo stars provide crucial
  constraints on the magnitude of the effects of helium diffusion. The
  flatness of the observed Li-T(eff) relation severely constrains
  diffusion Li isochrones, which tend to curve downward toward higher
  T(eff). It is argued that Li observations at the hot edge of the
  plateau are particularly important in constraining the effects
  of helium diffusion; yet, they are currently few in number. It is
  proposed that additional observations are required there, as well
  as below 5500 K, to define more securely the morphology of the halo
  Li abundances. Implications for the primordial Li abundance are
  considered. It is suggested that a conservative upper limit to the
  initial Li abundance, due to diffusive effects alone, is 2.35.

Title: Lithium in the Most Extreme Halo Stars; Trends with Metallicity
Authors: Deliyannis, Constantine P.; Demarque, Pierre
Bibcode: 1991ApJ...370L..89D
Altcode:
  A grid of extremely metal-poor stellar evolutionary tracks (Z =
  0.00001) is constructed to compare the predicted lithium abundance
  depletion to observations of the lithium abundance in correspondingly
  metal-poor stars (Fe/H = -3.3), and, combined with an earlier work to
  investigate trends of lithium isochrones with metal abundance. Lithium
  abundances in the most extreme halo stars hint at the possibility of
  small downward slope toward lower T(eff) in the flat Li-T(eff) relation
  (the Spite lithium plateau) observed in slightly less extreme stars;
  the models also predict this. In the cool star region of the Li-T(eff)
  plane, higher metallicity lithium isochromes are cooler at fixed lithium
  abundance, consistent with the observations. Current data thus agree
  well with the lithium trends from standard model.

Title: The Age Spread among Galactic Globular Clusters
Authors: Demarque, Pierre
Bibcode: 1991ppag.conf...45D
Altcode: 1991ppag.proc...45D; 1991LDP....14...45D
  No abstract at ADS

Title: Solar Calibration and the Ages of M67, NGC 188, and NGC 6791
Authors: Demarque, Pierre; Guenther, David B.; Green, Elizabeth M.
Bibcode: 1991ASPC...13..259D
Altcode: 1991fesc.book..259D
  No abstract at ADS

Title: Mixing due to Angular Momentum Transfer in Evolving Sun-Like
    Stars
Authors: Demarque, P.
Bibcode: 1991IAUS..145...71D
Altcode:
  No abstract at ADS

Title: Post-main-sequence solar evolution.
Authors: Demarque, Pierre; Guenther, David B.
Bibcode: 1991sia..book.1186D
Altcode:
  The authors' objective is to discuss some current research frontiers in
  solar-stellar physics. First, they describe and update the standard
  evolution of a 1-M<SUB><SUB>sun</SUB></SUB> star from the zero-age
  main sequence to the helium flash. Then, they focus on two areas
  of solar-stellar research which are presently in a state of rapid
  development. These two areas are: (1) the theory of solar and stellar
  nonradial acoustic (p-mode) oscillations, which can be used to test the
  pressure stratification in the stellar interior; and (2) the theory
  of the evolution of rotating stars, which predicts the evolution of
  surface rotational velocities and the mixing of chemical elements
  to the surface. The authors note in addition that oscillations and
  rotation are closely interrelated, because each individual p-mode is
  also split in frequency by internal rotation in the region through
  which it propagates. Observations of p-mode splittings thus can provide
  information on the state of rotation of the solar and stellar interiors.

Title: Ages of Globular Clusters
Authors: Demarque, P.; Deliyannis, C. P.; Sarajedini, A.
Bibcode: 1991ASIC..348..111D
Altcode: 1991otci.conf..111D
  No abstract at ADS

Title: Evolutionary Models of Halo Stars with Rotation. I. Evidence
    for Differential Rotation with Depth in Stars
Authors: Pinsonneault, Marc H.; Deliyannis, Constantine P.; Demarque,
   Pierre
Bibcode: 1991ApJ...367..239P
Altcode:
  Evolutionary models of metal-poor stars are computed including
  the effects of rotation, and their properties are compared
  with observations. The models rotate slowly at the surface, in
  agreement with the observed upper limits on the rotation velocity
  at main-sequence turnoff; they also have substantial differential
  rotation with depth. This differential rotation preserves a sufficient
  amount of internal angular momentum to explain the rapid rotation of
  evolved horizontal-branch stars. These results hold for a wide range
  of angular momentum loss and transport parameter values. Differences
  and similarities between the surface and internal rotation of solar
  metallicity and metal-poor models are discussed. Rigidly rotating
  models are found to be incompatible with the observations once giant
  branch mass loss is taken into account. Horizontal-branch rotation
  velocity measurements as a function of color are proposed as a test
  of the rotation law enforced in convection zones, and their dependence
  on cluster age and metallicity are discussed.

Title: A New Age Diagnostic Applied to the Globular Clusters NGC
    288 and NGC 362
Authors: Sarajedini, Ata; Demarque, Pierre
Bibcode: 1990ApJ...365..219S
Altcode:
  A new age diagnostic for globular clusters is described which uses
  the difference between the turnoff and the base of the giant branch
  as the age indicator. As a first application, it is shown that there
  is a difference in age of 3.1 + or - 0.9 Gyr between the classic
  'second parameter' pair NGC 288 and NGC 362. The existence of this age
  difference is independent of metal abundance differences between the two
  clusters of up to 0.5 dex. This age difference is corrected for various
  combinations of relative oxygen enhancement, and it is concluded that
  the difference in age remains significant for all plausible scenarios.

Title: Rotation of Low-Mass Stars: A New Probe of Stellar Evolution
Authors: Pinsonneault, M. H.; Kawaler, Steven D.; Demarque, P.
Bibcode: 1990ApJS...74..501P
Altcode:
  Models of stars of various masses and rotational parameters were
  developed and compared with observations of stars in open clusters of
  various ages in order to analyze the evolution of rotating stars from
  the early premain sequence to an age of 1.7 x 10 to the 9th yrs. It is
  shown that, for stars older than 10 to the 8th yrs and less massive
  than 1.1 solar mass, the surface rotation rates depend most strongly
  on the properties of the angular momentum loss. The trends of the
  currently available observations suggest that the rotation periods
  are a good indicator of the field-star ages.

Title: Effects of Helium Diffusion on Globular Cluster Ages Inferred
    from Isochrones
Authors: Chaboyer, B.; Deliyannis, C. P.; Demarque, P.; Pinsonneault,
   M. H.; Sarajedini, A.
Bibcode: 1990BAAS...22.1205C
Altcode:
  No abstract at ADS

Title: Primordial Lithium, Stellar Evolution, Big Bang Cosmology,
    and Dark Matter
Authors: Deliyannis, C. P.; Demarque, P.; Pinsonneault, M. H.
Bibcode: 1990BAAS...22.1214D
Altcode:
  No abstract at ADS

Title: The Effects of the MHD Equation of State and Molecular
    Opacities on the Oscillation Spectrum of the Standard Solar Model
Authors: Kim, Y. -C.; Demarque, P.; Guenther, D. B.
Bibcode: 1990BAAS...22Q1207K
Altcode:
  No abstract at ADS

Title: Effects of Main Sequence Rotational Mixing on Surface CNO
    Abundances in Red Giant Branch Stars
Authors: Pinsonneault, M. H.; Demarque, P.; Sofia, S.; Deliyannis,
   C. P.
Bibcode: 1990BAAS...22.1206P
Altcode:
  No abstract at ADS

Title: The Evolution of Horizontal-Branch Stars: Theoretical Sequences
Authors: Lee, Young-Wook; Demarque, Pierre
Bibcode: 1990ApJS...73..709L
Altcode:
  A new grid of standard (i.e., solar CNO/Fe, no core rotation, and
  including semiconvection) horizontal-branch evolutionary sequences
  are presented which extend the grid of Sweigart both by including the
  final phase of core helium exhaustion and by using a finer grid of
  compositions. These sequences were constructed specifically for the
  studies of the Sandage period-shift effect and the second parameter
  phenomenon among the Galactic globular clusters. The numerical
  results for the observable characteristics of the sequences are
  tabulated which can be directly used to synthesize the observed
  horizontal-branch distributions. The present computations suggest
  that the observed difference in period change of RR Lyrae stars in the
  globular clusters M3 and M15 could be attributed, at least in the mean,
  to stellar evolution.

Title: Lithium in Halo Stars from Standard Stellar Evolution
Authors: Deliyannis, Constantine P.; Demarque, Pierre; Kawaler,
   Steven D.
Bibcode: 1990ApJS...73...21D
Altcode:
  A grid has been constructed of theoretical evolution sequences of models
  for low-metallicity stars from the premain-sequence to the giant branch
  phases. The grid is used to study the history of surface Li abundance
  during standard stellar evolution. The Li-7 observations of halo stars
  by Spite and Spite (1982) and subsequent observations are synthesized
  to separate the halo stars by age. The theory of surface Li abundance
  is illustrated by following the evolution of a reference halo star
  model from the contracting fully convective premain sequence to the
  giant branch phase. The theoretical models are compared with observed
  Li abundances. The results show that the halo star lithium abundances
  can be explained in the context of standard stellar evolution theory
  using completely standard assumptions and physics.

Title: The Horizontal-Branch Stars in Globular Clusters. I. The
    Period-Shift Effect, the Luminosity of the Horizontal Branch, and
    the Age-Metallicity Relation
Authors: Lee, Young-Wook; Demarque, Pierre; Zinn, Robert
Bibcode: 1990ApJ...350..155L
Altcode:
  Synthetic models of the horizontal branches in globular clusters are
  constructed from a grid of the standard horizontal branch evolutionary
  tracks. The models are used to study the period shifts at constant
  T(eff) between RR Lyrae variables in globular clusters of different
  metallicities and the variation in horizontal-branch luminosity with the
  Fe/H ratio. The results suggest that the observed differences in the
  mean periods of the ab variables and the fraction of c-type variables
  between the two Oosterhoff groups are caused by a difference in the
  mean luminosity of the ab variables of about 0.18 bolometric mass and
  by the uneven distribution of variables across the instability strip
  in the group II clusters.

Title: The Effects of Internal Stellar Rotation on Age Estimates
    for Globular Cluster Stars
Authors: Deliyannis, C. P.; Demarque, P.; Pinsonneault, M. H.
Bibcode: 1990BAAS...22..746D
Altcode:
  No abstract at ADS

Title: On the Period-Shift Effect of the Field Rr-Lyrae Stars and
    the Ages of Galactic Globular Clusters
Authors: Lee, Y. W.; Demarque, P.; Zinn, R.
Bibcode: 1990aadm.conf..275L
Altcode:
  No abstract at ADS

Title: The Seismology of Sun-like Stars
Authors: Demarque, P.; Guenther, D. B.
Bibcode: 1990LNP...367..405D
Altcode: 1990psss.conf..405D
  By observing the p-mode oscillation spectrum of a star and determining
  its first and second order frequency spacings, v and , it is possible
  to obtain constraints which are useful in modeling the star. We show,
  as an example, how the positions of the frequencies of the p-modes
  changes from the familiar picket fence or regular spacing to a more
  random irregular spacing as the sun evolves from the ZAMS to the base of
  the giant branch. For Cen, Eri, Procyon, Arcturus, and Cas we describe,
  in specific terms, how the frequency spacings can be used to improve
  our knowledge about each of these stars. We discuss the important
  advantages of observing the p-modes of stars in star clusters. We also
  discuss how rotational splittings could be used along with other stellar
  diagnostics to infer the rotational history of the star's interior.

Title: Evolutionary Models Of Metal Poor Stars With Rotation
Authors: Pinsonneault, M. H.; Deliyannis, C. P.; Demarque, P.
Bibcode: 1990BAAS...22..746P
Altcode:
  No abstract at ADS

Title: The Ages of Globular Cluster Stars: Effects on Rotation of
    Pre--Main-Sequence, Main-Sequence, and Turnoff Evolution
Authors: Deliyannis, Constantine P.; Demarque, Pierre; Pinsonneault,
   Marc H.
Bibcode: 1989ApJ...347L..73D
Altcode:
  Evolutionary sequences for low-metallicity stars (Z ranging from 0.001
  to 0.0001) to study the effects of internal stellar rotation on the
  evolutionary time scales in the pre-main sequence, the main sequence
  (MS), and around the MS turnoff. Although a substantial amount of
  angular momentum remains in the interior, rotation is only a minor
  perturbation on the structure and ages of globular cluster stars. Even
  models with large initial angular momenta have MS lifetimes that
  are within 1 percent of those of standard models of the same mass
  and composition. Therefore, rotation does not affect age estimates
  of globular clusters from isochrone fitting. Furthermore, the models
  suggest that because rotation is not likely to affect horizontal-branch
  (HB) morphology, it does not affect significantly age estimates from
  the Delta-V method. Nevertheless, the internal angular momentum in the
  models is consistent with observations of surface rotational velocities
  on the HB, which require the preservation of a large reservoir of
  internal angular momentum.

Title: The Standard Solar Model: Composition, Opacities, and
    Seismology
Authors: Guenther, D. B.; Jaffe, A.; Demarque, P.
Bibcode: 1989ApJ...345.1022G
Altcode:
  High-precision standard solar models are used to investigate
  systematically the implications of current uncertainties in the interior
  radiative opacities for both the derivation of the helium content Y
  and the modeling of p-mode oscillation frequencies of the sun. The
  differences between the Cox-Stewart solar opacities and the Los Alamos
  Opacity Library solar opacities are found to be due principally to
  differences in the absorption coefficients themselves. The uncertainty
  of Ne in the solar chemical composition is shown to result in only a
  small uncertainty in Y. In the standard model framework, the uncertainty
  in Y is between 0.29 and 0.27. Only a small dependence of the asymptotic
  spacing of p-modes on chemical composition is detected. The effects of
  dependence on Y of the adiabatic exponent Gamma(1) and of the density of
  the structure of the outer layers is not monotonic because both these
  variables depend on the complex interplay of H and He ionization. The
  greatest sensitivity of sound speed to chemical composition is found
  below the surface convection zone.

Title: A Map-based Determination of the Nature of Beta Delphini
Authors: Gatewood, George; Castelaz, Michael; Persinger, Timothy;
   Stein, John; Demarque, Pierre; Sofia, Sabatino; Stephenson, Bruce
Bibcode: 1989ApJ...342.1085G
Altcode:
  The Beta Delphini binary system presents a stringent test of the theory
  of stellar evolution. Improved parallax and component masses are found
  for its giant (F5 III and F5 IV) stars. A study of the evolutionary
  status of the system indicates it to be 1.9 Gyr (1.9 billion years)
  old and to have a metallicity of approximately 1.5 times that of the
  Sun. The perturbation due to the 26.6 yr orbital motion is clearly
  shown in this 2.2 yr study and allows the most precise determination
  of the relative masses of the component stars to date. The next few
  months present an unusual opportunity for orbital study as the system
  passes through periastron. Two of the reference stars are found to
  have distances of less than 100 parsecs.

Title: Primordial lithium and the standard model(s)
Authors: Deliyannis, Constantine P.; Demarque, Pierre; Kawaler,
   Steven D.; Krauss, Lawrence M.; Romanelli, Paul
Bibcode: 1989PhRvL..62.1583D
Altcode:
  We present the results of new theoretical work on surface
  <SUP>7</SUP>Li and <SUP>6</SUP>Li evolution in the oldest halo stars
  along with a new and refined analysis of the predicted primordial
  lithium abundance resulting from big-bang nucleosynthesis. This
  allows us to determine the constraints which can be imposed upon
  cosmology by a consideration of primordial lithium using both
  standard big-bang and standard stellar-evolution models. Such
  considerations lead to a constraint on the baryon density today of
  0.0044&lt;Ω<SUB>b</SUB>h<SUP>2</SUP>&lt;0.025 (where the Hubble
  constant is 100h Km sec<SUP>-1</SUP> Mpc <SUP>-1</SUP>), and impose
  limitations on alternative nucleosynthesis scenarios.

Title: Evolutionary Models of the Rotating Sun
Authors: Pinsonneault, M. H.; Kawaler, Steven D.; Sofia, S.;
   Demarque, P.
Bibcode: 1989ApJ...338..424P
Altcode:
  A new rotating stellar evolution code is developed and applied to
  the sun. A hydrostatic fully convective premain-sequence model is
  evolved to the age of the sun. As the model evolves, it accounts
  for angular-momentum loss via a magnetic wind and angular-momentum
  redistribution by rotationally induced instabilities. The resulting
  models have an oblateness in agreement with observed upper limits. The
  rotation curves show two main features: the outer layers exhibit
  minimal radial differential rotation, and a rapidly rotating central
  core is preserved. These basic features persist through a wide range
  of model parameters.

Title: Evidence for a spread in ages among galactic globular clusters:
    age as the second parameter in NGC 288 and NGC 362.
Authors: Demarque, P.; Lee, Y. -W.; Zinn, R.; Green, E. M.
Bibcode: 1989asgc.conf...97D
Altcode:
  The differences in the C-M diagrams of NGC 288 and NGC 362 are
  discussed in the light of recent advances in the understanding of the
  horizontal-branch (HB), together with theoretical isochrones and CCD
  observations of their main sequence turnoffs. The authors show that
  consistency with current stellar evolution and pulsation theory can
  only be achieved if age (and not helium or oxygen abundance differences)
  is the second parameter of HB morphology.

Title: Is the Sun really a rigid rotator?
Authors: Demarque, P.; Guenther, D. B.
Bibcode: 1988ESASP.286...99D
Altcode: 1988ssls.rept...99D
  Attention is drawn to observations of surface rotational periods
  in subgiants which indicate that a deep-seated reservoir of angular
  momentum must exist in these stars. This interpretation is compatible
  with theoretical studies of the rotational history of the Sun and
  sun-like stars, but is in apparent conflict with observations of p-mode
  splittings in the Sun. In order to understand better the source of
  this apparent discrepancy, the authors explore the predicted rotational
  splittings of the several test rotation curves and compare them to the
  solar data. Finally, they discuss the implications of their findings
  for solar structure.

Title: Primordial lithium and the standard model(s).
Authors: Deliyannis, C. P.; Demarque, P.; Kawaler, S. D.; Krauss,
   L. M.; Romanelli, P.
Bibcode: 1988plsm.book.....D
Altcode:
  The authors present the results of new theoretical work on surface
  <SUP>7</SUP>Li and <SUP>6</SUP>Li evolution in the oldest halo stars
  along with a new and refined analysis of the predicted primordial
  lithium abundance resulting from big-bang nucleosynthesis. This
  allows to determine the constraints which can be imposed upon
  cosmology by a consideration of primordial lithium using both standard
  big-bang and standard stellar evolution models. Such considerations
  lead to a constraint on the baryon density today of 0.0044 &lt;
  Ω<SUB>b</SUB>h<SUP>2</SUP> &lt; 0.025, and impose limitations on
  alternative nucleosynthesis scenarios.

Title: Probing the Sun's Internal Rotation
Authors: Demarque, P.; Guenther, D. B.
Bibcode: 1988BAAS...20R1009D
Altcode:
  No abstract at ADS

Title: GONG Solar Model Workshop Yale Center for Solar and Space
    Research 1987MAY27-29
Authors: Demarque, P.; Christensen-Dalsgaard, J.; Guenther, D. B.
Bibcode: 1988ComAp..12..157D
Altcode:
  No abstract at ADS

Title: Isochrone Comparisons Stellar Physics and Implications for
    Stellar Ages
Authors: Demarque, P.; Guenther, D. B.; King, C. R.; Green, E. M.
Bibcode: 1988csa..proc..101D
Altcode: 1988LDP....10..101D
  In this paper, the authors address primarily problems of stellar
  interior physics and their implications for the calibration of
  stellar ages.

Title: On the Bimodal Distrubutions of Horizontal Branches
Authors: Lee, Young-Wook; Demarque, Pierre; Zinn, Robert
Bibcode: 1988IAUS..126..505L
Altcode:
  New synthetic horizontal branch (HB) models are presented for some
  globular clusters known to have bimodal HB distributions.

Title: Sensitivity of Solar P-Modes to Solar Envelope Structure
Authors: Demarque, P.; Guenther, D. B.
Bibcode: 1988IAUS..123...91D
Altcode:
  The authors present a study of the effects of diffusion of helium
  and heavy elements from the convection zone into the radiative layer
  immediately below the convection zone, on the structure of the solar
  envelope. A comparison is made of the p-mode oscillation spectrum and
  the run of the speed of sound in a model with diffusion, in a standard
  model, and with observation.

Title: The Origin of Old Hot Stars in Super-Metal Stellar Systems
Authors: Demarque, P.; Pinsonneault, M.
Bibcode: 1988ASPC....1..371D
Altcode: 1988posh.conf..371D
  Super-metal-rich (SMR) stars are observed in the bulges of elliptical
  galaxies and are believed to be a major component of the stellar
  population in elliptical galaxies. The authors present first results
  based on evolutionary calculations of SMR stars of low mass. They find
  that stellar evolution theory predicts the existence of an increased
  ratio of hot to cool stars in old SMR stellar populations, using
  standard estimates for mass loss and chemical enrichment.

Title: Isochrone Fitting of Color Magnitude Diagrams of Old Star
    Clusters - Implications for Stellar Ages
Authors: King, C. C.; Demarque, P.; Green, E. M.
Bibcode: 1988csa..proc..211K
Altcode: 1988LDP....10..211K
  No abstract at ADS

Title: Evidence for a spread in ages among galactic globular clusters:
    age is the second parameter in NGC288 and NGC362
Authors: Demarque, P.; Lee, Y. W.; Zinn, R.; Green, E. M.
Bibcode: 1988asgc.conf...97D
Altcode:
  No abstract at ADS

Title: Internal Constitution and Oscillation Spectrum of Procyon
Authors: Demarque, P.; Guenther, D. B.
Bibcode: 1988IAUS..123..287D
Altcode:
  The aim of this paper is to explore theoretically the potential ability
  of the p-mode and g-mode non-radial oscillation spectrum to throw
  light on two fundamental problems raised by the authors' first study:
  Procyon A's evolutionary status, and its mass-luminosity relation.

Title: Globular cluster luminosity functions
Authors: Demarque, P.
Bibcode: 1988IAUS..126..121D
Altcode:
  The use of luminosity functions in determining the helium content,
  age, and initial mass function of globular clusters, and in testing
  the stellar structure theory is reviewed. The main sequence turnoff
  and subgiant phases are examined. The Thomas (1967) peak in the
  luminosity function and the gap near the base of the giant branch of
  globular clusters found in the CM are discussed as probes of stellar
  structure. Research in the area of faint star photometry, dealing with
  the lower main sequence luminosity function and the interplanetary
  magnetic field is presented.

Title: Synthetic Models of the Horizontal Branch and the Calibration
    of Globular Clusters Ages
Authors: Lee, Y. W.; Demarque, P.; Zinn, R.
Bibcode: 1988csa..proc..149L
Altcode: 1988LDP....10..149L
  In this paper, the authors summarize their progress in construction
  of synthetic models of the horizontal branch from stellar evolutionary
  tracks. Many of the details of their method are described in an earlier
  progress report (Lee, Demarque, and Zinn 1987).

Title: ICCD Speckle Observations of Binary Stars. III. A Survey for
    Duplicity Among High Velocity Stars
Authors: Lu, Phillip K.; Demarque, Pierre; van Altena, William;
   McAlister, Harold; Hartkopf, William
Bibcode: 1987AJ.....94.1318L
Altcode:
  A survey program to identify binary candidates among high-velocity dwarf
  stars using the GSU speckle camera has been carried out. The purposes
  of this study are: (1) to determine the binary frequency of the halo
  population to provide information on the star-formation processes in
  the galactic halo; and (2) to eventually derive the orbital elements
  of the newly discovered binaries. In this paper, the authors report
  speckle interferometry data that have been obtained and analyzed
  for a sample of 182 stars. Based on these data, ten stars are found
  to be binary. The authors find that their data are compatible with a
  total frequency for high-velocity long-period doubles as large as for
  low-velocity stars. Distances have been estimated for the ten binary
  stars using their spectroscopic parallaxes and visual magnitudes. Of
  these ten stars, all are within 100 pc of the Sun and eight have
  linear separations &lt;20 AU. Using the mass-luminosity relation and
  assuming circular orbits, four stars are found to have periods less
  than 20 yr. These ten candidates will be monitored to determine their
  orbital elements.

Title: The Evolution of Red Clump Stars: Theoretical Sequences
Authors: Seidel, E.; Demarque, P.; Weinberg, D.
Bibcode: 1987ApJS...63..917S
Altcode:
  Two grids of horizontal-branch evolutionary sequences are presented
  which extend the grid of Sweigart and Gross (1976) to higher masses and
  higher metallicities. These two grids were constructed specifically
  for the study of red clump stars observed in intermediate-age star
  clusters in the Magellanic Clouds and in the Galaxy. An additional
  evolutionary track, with a thick hydrogen-burning shell which simulates
  the effect of a modest amount of mixing from the helium core into the
  shell at the time of the helium-core flash, is also presented. It is
  found that a small amount of mixing does not alter in a significant
  way the standard course of horizontal-branch evolution.

Title: Intermediate-Age Core Helium-burning Stars and the Distance
    to the Magellanic Clouds
Authors: Seidel, E.; Da Costa, G. S.; Demarque, Pierre
Bibcode: 1987ApJ...313..192S
Altcode:
  The luminosities of the core helium burning stars in six Magellanic
  Cloud intermediate-age star clusters, whose ages have recently been
  determined from photometry reaching below the main-sequence turnoff,
  are compared with the predictions of a new grid of theoretical
  models. It is found that for the so-called 'short' distance moduli
  consistent results can be achieved with moderate amounts of mass
  loss from the main sequence to the core helium burning stage for the
  older clusters, and with rather more substantial mass loss for the
  younger objects. For the 'long' moduli, however, the results of the
  comparison give inconsistent results in that the required masses for
  the clump stars generally exceed the corresponding turnoff masses,
  in some cases by several tenths of a solar mass. The results support
  the adoption of smaller distances to these galaxies.

Title: The solar-stellar connection: Internal rotation in low-mass
    stars
Authors: Demarque, Pierre
Bibcode: 1987ASSL..137..121D
Altcode: 1987isav.symp..121D
  The problem of the internal rotation of stars with masses and internal
  evolution similar to the sun is investigated, emphasizing the need
  to construct models of stellar convection zones which are consistent
  with full interior models. The affect of the distribution of angular
  momentum within a star on the formation process in a gas cloud and on
  the internal evolution throughout the premain-sequence phase and the
  early postmain-sequence phase is considered. The generation of magnetic
  fields associated with chromospheric activity via the interaction of
  rotation with convection is discussed. It is noted that rotationally
  induced mixing can alter the rate of evolution, thus affecting the
  luminosity function of star clusters.

Title: The revised Yale isochrones and luminosity functions
Authors: Green, Elizabeth M.; Demarque, Pierre; King, Christopher R.
Bibcode: 1987ryil.book.....G
Altcode:
  No abstract at ADS

Title: Evolutionary Models of the Rotating Sun (Invited review)
Authors: Sofia, Sabatino; Pinsonneault, Marc; Kawaler, Steven D.;
   Demarque, Pierre
Bibcode: 1987LNP...291..205S
Altcode: 1987csss....5..205S
  This paper reviews current work on the evolution of a differentially
  rotating solar model. Although we discuss global features of
  the evolution with rotation in general terms, the specific models
  described are those computed with the new Yale Rotating Evolution Code
  (YREC). YREC uses the Kippenhahn and Thomas (1970, KT) formalism
  as implemented by Endal and Sofia (1976), although the numerical
  formulation of our code is totally new. Particular calculations that
  we describe include the effects of different initial total angular
  momentum, the consequences of varying the properties and magnitude
  of angular momentum losses by wind torquing, and the consequences
  of specific composition and angular momentum redistribution
  mechanisms. This paper is a progress report which points out the
  complexity of the problem, and the need for a broad-based observational
  program to solve it. Because the final solution is not yet in hand,
  we outline the steps that, in our estimation, need to be undertaken
  in order to make progress.

Title: Synthetic horizontal branch models for globular clusters:
    the luminosity of the horizontal branch and the Oosterhoff effect.
Authors: Lee, Young-Wook; Demarque, Pierre; Zinn, Robert
Bibcode: 1987fbs..conf..137L
Altcode: 1987IAUCo..95..137L; 1987LDP.....8..137L
  The variation of horizontal-branch (HB) luminosities with metal
  abundances is analyzed on the basis of HB models synthesized from
  theoretical HB evolutionary tracks. The focus is on the Oosterhoff
  effect, as related to period shifts in globular-cluster RR Lyr
  variables. The construction of the models and the Oosterhoff period
  groups is explained in detail, and the implications for globular-cluster
  ages are considered. The ratio of Delta M(bol) (RR) to Delta Fe/H
  for the HB is calculated as 0.24, slightly steeper than that found by
  Sandage (1981 and 1982).

Title: An Astrometry Explorer
Authors: York, D.; Jones, B.; Demarque, P.; Faber, S.; Hughes, J.;
   Johnston, K.; Lin, D.; Silverglate, P.; van Altena, W.
Bibcode: 1986BAAS...18.1012Y
Altcode:
  No abstract at ADS

Title: The Stellar Seismology of epsilon Eridani
Authors: Guenther, D. B.; Demarque, P.
Bibcode: 1986ApJ...301..207G
Altcode:
  This calculated p-mode oscillation spectrum of several stellar models
  of ɛ Eridani are compared with the observational data of Noyes
  et al. Specifically, models with different masses, metallicities,
  and mixing length parameters are constructed, and for each model
  the low-degree p-mode oscillation spectrum is calculated and its
  characteristic frequency spacing is compared with the observed value of
  172 μHz. Of all the models constructed, the model with a mass of 0.80
  M_sun;, Z = 0.02, mixing length parameter α = 1.00, an age of 11.5
  Gyr, and a radius of 0.80 R_sun; best fits the observed luminosity,
  effective temperature, and oscillation data. The characteristic
  frequency spacing of the oscillation spectrum of this model is 170
  μHz. It is concluded that the structure of this model must be very
  close to the actual physical structure of ɛ Eri.

Title: Interior Models for Procyon A: Evolutionary Status and
    Oscillation Properties
Authors: Demarque, P.; Guenther, D. B.
Bibcode: 1986LNP...254..187D
Altcode: 1986csss....4..187D
  Evolutionary sequences have been constructed to determine the
  evolutionary status of Procyon A. We find that Procyon could be in any
  of the following three evolutionary phases: (a) core hydrogen burning;
  (b) core exhaustion; (c) hydrogen burning shell narrowing. However,
  both timescale and luminosity arguments strongly favor possibility (a).

Title: The Case of alpha Centauri: Mass, Age, and p-Mode Oscillation
    Spectrum
Authors: Demarque, P.; Guenther, D. B.; van Altena, W. F.
Bibcode: 1986ApJ...300..773D
Altcode:
  The authors have investigated the astrometric and physical properties
  of the α Centauri system, a nearby visual binary which shares a common
  space motion with the nearest star Proxima Cen. First, the parallax
  of the binary system is estimated to be 0arcsec.7506±0arcsec.0046
  (s.e.). Using this absolute parallax, the masses of α Cen A and B are
  respectively 1.09±0.01 and 0.90±0.01 M_sun;. Second, the evolutionary
  status of α Cen A and B is determined with the help of theoretical
  stellar models. Evolutionary tracks yield the age of the α Cen system
  as a function of metallicity. The discussion points to a consistent
  model with an age in the vicinity of 4 - 4.5×10<SUP>9</SUP>yr. Third,
  the nonradial oscillations of α Cen A are considered. The p-mode
  spectrum of the models of α Cen A is compared to that of the Sun and
  to the observations of Fossat et al. It is concluded that Fossat et
  al.'s observations are inconsistent with p-mode spectra constructed
  from standard theoretical models.

Title: The luminosity function on the subgiant branch of 47 Tucanae :
    a comparison of observation and theory.
Authors: King, C. R.; Da Costa, G. S.; Demarque, P.
Bibcode: 1985ApJ...299..674K
Altcode:
  Photographic photometry has been obtained for 1200 stars in the
  magnitude range of V = 13.5 to 17.5 in the field of the Galactic
  globular cluster 47 Tucanae and used to form both a color-magnitude
  diagram and a luminosity function. No gap at the base of the giant
  branch of size similar to those recently reported in other clusters was
  detected, but a prominent peak is present in the luminosity function
  at a level approximately 0.5 mag below the horizontal branch. This
  peak is identified with that which results from the passage of the
  hydrogen-burning shell through the composition discontinuity left by the
  deepest penetration of the convective envelope of the star. However,
  the observed peak is nearly 1 mag fainter than the prediction of
  standard stellar evolution theory for the age and composition of this
  cluster. The most plausible explanation for this discrepancy is that
  it results from overshoot at the base of the convective envelope of
  the stars. An overshoot of approximately one local pressure scale
  height is sufficient to produce agreement with the observations.

Title: Binary Survey Among High Velocity Stars Using GSU Speckle
    Camera
Authors: Lu, P. K.; Demarque, P.; van Altena, W.; Hartkopf, W.;
   McAlister, H.
Bibcode: 1985BAAS...17Q.904L
Altcode:
  No abstract at ADS

Title: The Solar-Stellar Connection: II. - Stellar Studies
Authors: Demarque, P.
Bibcode: 1985BAAS...17..898D
Altcode:
  No abstract at ADS

Title: From solar dynamo to terrestrial climate
Authors: Sofia, S.; Demarque, P.; Endal, A.
Bibcode: 1985AmSci..73..326S
Altcode:
  Recent progress made in measuring and characterizing variations in
  the global solar energy output are surveyed. The most reliable data
  on variations are gathered by spacecraft, most recently by Nimbus 7
  and the SMM. The longest irradiance decrements are associated with
  the appearance of large sunspots, particularly at the center of the
  solar disk. Faculae, bright spots appearing with sunspots, redirect
  radiation to directions other than perpendicular. Global variations
  average less than 0.1 percent of the average annual irradiance, although
  some long-term drift may be occurring. Astrometric data on Mercury
  transit across the solar disk have, with 250 yr cumulative data,
  revealed no more than 0.2 arcsec variations in the solar diameter,
  while eclipse data indicate variations of up to 0.6 arcsec in recent
  epochs. Other data, however, have connected the diameter variations
  with magnetic field increases. A deeper understanding of the physics
  of the solar dynamo will be required to detect the significance of
  the observed changes relative to irradiance averages.

Title: Current Problems in Horizontal Branch Theory - Implications
Authors: Demarque, P.
Bibcode: 1985cto..conf..268D
Altcode: 1985IAUCo..82..268D
  No abstract at ADS

Title: Convective heating of the inner core of red giants prior to
    the peak of the core helium flash
Authors: Cole, P. W.; Demarque, P.; Deupree, R. G.
Bibcode: 1985ApJ...291..291C
Altcode:
  The effects of convective overshooting across the temperature inversion
  in red giant cores have been investigated theoretically, using a
  two-dimensional and three-dimensional hydrodynamic model of the core
  helium flash. The model is based on a simple heating algorithm which can
  be easily incorporated into a variety of stellar evolution codes. On
  the basis of the numerical results it is found that: (1) convective
  overshooting led to substantial heating of the material underneath
  the temperature inversion, producing a smoother temperature profile;
  (2) up until one week before the time of maximum temperature, interior
  heating is unimportant, but alters the standard relation of maximum
  temperature and density at the point of maximum temperature; and
  (3) overshooting redistributed the mass from the location of maximum
  temperature. The contribution of internal heating to the subsequent
  evolution of the core of a red giant is also discussed. Model estimates
  of the selected properties of core helium flash sequences at the time
  of maximum temperature are given in a table.

Title: Mass Loss on the Blue Horizontal Branch and the Origin of
    the Subdwarf B Stars
Authors: Demarque, Pierre; Eder, Jo-Ann
Bibcode: 1985hbuv.proc...91D
Altcode: 1985LDP.....6...91D
  The authors have investigated the effects of mass loss on the evolution
  of blue horizontal-branch stars. They find that mass loss rates in the
  range 2.5×10<SUP>-10</SUP> &lt; M &lt; 1×10<SUP>-9</SUP>M_sun;/year
  are needed to explain the existence of the subdwarf B stars.

Title: The resonant count diagram and solar g mode oscillations.
Authors: Guenther, D. B.; Demarque, P.
Bibcode: 1984sses.nasa..349G
Altcode: 1984sss..conf..349G
  Evidence is provided to support the hypothesis that, because of the
  particular frequency separations of the solar g modes, resonant
  three-wave interactions stimulate only a selected few g modes. A
  resonant count diagram was obtained by plotting the total number of
  possible resonant three-wave interactions or a given beat frequency
  against the inverse of the beat frequency (the beat period), within
  a given frequency tolerance. The 1 = 1, 2, 3, 4 g modes calculated by
  Christensen-Dalsgaard, Gough and Morgan (1979) for a standard model of
  the Sun were used. The diagram has a significant peak at 160 minutes
  as well as other peaks at longer periods. The g modes that Delache and
  Scherrer (1983) tentatively identified from the Crimea-Stanford data
  were also plotted. These modes were found to correspond with the other
  peaks in the diagram. This coincidence between the observed g modes
  and the peaks in the resonant count diagram suggest that the observed
  g modes do owe their observability to resonant three-wave interactions.

Title: An interpretation of the gap on the subgiant branch of several
    globular clusters
Authors: Armandroff, T. E.; Demarque, P.
Bibcode: 1984A&A...139..305A
Altcode:
  Four globular clusters whose color-magnitude diagrams show a gap
  on the subgiant branch are discussed. Standard stellar evolution
  theory does not predict the existence of a rapid phase of evolution
  at this point during a star's lifetime. A mechanism is outlined where
  this rapid evolutionary phase is attributed to the hydrogen-burning
  shell passing through a discontinuity in chemical composition. This
  discontinuity is set up by an ad-hoc mixing process. Evolutionary tracks
  constructed result in a gap crossing time a factor of two smaller
  than the standard model and almost identical evolution outside the
  gap. Another possibility, that the gap is caused by a rapid change in
  atmopsheric structure, is investigated by varying the mixing length
  in the convection zone. Tracks constructed in this manner are not
  consistent with the observed gaps.

Title: The Revised Yale Isochrones and Luminosity Functions
Authors: Green, E. M.; Demarque, P.; King, C. R.
Bibcode: 1984BAAS...16..997G
Altcode:
  No abstract at ADS

Title: Comparing α Cen with the Sun: Chemical Composition,
    Mixing-length, Age, and p-Mode Oscillation Spectrum
Authors: Demarque, P.; Guenther, D. B.
Bibcode: 1984BAAS...16.1001D
Altcode: 1984BAAS...16.1000D
  No abstract at ADS

Title: AM. 06 An Astrometry Satellite
Authors: York, D. G.; Jones, B.; Faber, S.; Lin, D.; van Altena, W.;
   Demarque, P.; Hughes, J.; Johnston, K.; Bunner, A.
Bibcode: 1984BAAS...16..775Y
Altcode:
  No abstract at ADS

Title: The Luminosity Function on the Subgiant Branch of 47 Tuc:
    A Comparison of Observation and Theory
Authors: King, C. R.; Da Costa, G. S.; Demarque, P.
Bibcode: 1984BAAS...16..529K
Altcode:
  No abstract at ADS

Title: Convective Heating of the Inner Core During the Core Helium
    Flash
Authors: Cole, P. W.; Demarque, P.; Deupree, R. G.
Bibcode: 1984BAAS...16..526C
Altcode:
  No abstract at ADS

Title: The Subgiant Branch Gap in Several Globular Clusters
Authors: Demarque, P.; Armandroff, T. E.
Bibcode: 1984BAAS...16..526D
Altcode:
  No abstract at ADS

Title: Resonant three-wave interactions of solar g-modes
Authors: Guenther, D. B.; Demarque, P.
Bibcode: 1984ApJ...277L..17G
Altcode:
  The observed g-mode oscillation spectrum of the sun is compared with
  a plot of the number of possible resonant three-wave interactions of
  theoretical g-modes at a given period versus the frequency difference
  of the coupled modes. A very large peak is found near 160 minutes,
  corresponding to the well-known 160-minute solar oscillation. Peaks
  in the curve are also found to coincide with the recently identified
  g-mode data of Delache and Scherrer (1983).

Title: Resonant Three-Wave Interactions and an Application to Solar
    G Mode Oscillations
Authors: Guenther, D. B.; Demarque, P.
Bibcode: 1984IAUS..105...67G
Altcode:
  The authors present some initial results of a long-term investigation
  of resonant three-wave interactions in the solar interior, which
  indicate that these nonlinear interactions take place in the sun and
  are, in fact, responsible for the observed g mode spectrum.

Title: Helium abundances in globular star clusters
Authors: Cole, P. W.; Demarque, P.; Green, E. M.
Bibcode: 1983prhe.work..235C
Altcode:
  New results involving the determination of the abundances in galactic
  halo stars by examining the slopes of the subgiant luminosity functions
  in globular clusters and the R-method are reported. Theoretical
  luminosity functions for an age of 16 billion yr are applied to He
  abundances of 0.20-0.30, with error ranges included for 2000 stars in
  a 3 magnitude interval above the main sequence turn-off. The R method,
  comprising the ratio of theoretical horizontal branch (HB) to red
  giant (RG) lifetimes, is shown to be a function of the He abundance,
  since an He flash precedes the HB evolutionary phase and is associated
  with an He abundance of 0.16-0.23, which approaches Big Bang theory
  predictions of 0.24.

Title: Evolution of a population III star of low mass
Authors: Guenther, D. B.; Demarque, P.
Bibcode: 1983A&A...118..262G
Altcode:
  An evolutionary track for a metal-free star of low mass with parameters
  (M/M_sun;, X, Z)=(0.90, 0.80, 0.00) has been constructed from the main
  sequence to the base of the giant branch. It has been found that,
  although the evolutionary path of the star near the main sequence
  is similar to that of a star of very low metallicity, its internal
  structure is not. The zero-metallicity star failed to exhaust
  its central hydrogen. It maintained a trace amount of hydrogen
  in the core, through turnoff, up to the base of the giant branch
  where enough carbon was produced at the center by the triple-alpha
  reaction to start CN-burning. A convective core was formed which
  grew so rapidly that the calculations had to be terminated. Possible
  subsequent evolutionary outcomes are discussed, all of which suggest
  that compared to low-metallicity stars, the time spent in the giant
  phase will be sharply reduced.

Title: The ages and compositions of old clusters.
Authors: Janes, K.; Demarque, P.
Bibcode: 1983ApJ...264..206J
Altcode:
  From published color-magnitude diagrams of 23 globular and open
  clusters the authors have measured the mean color index or absolute
  magnitude at various points along the principal sequences. By
  relating these quantities to the analogous parameters derived from
  theoretical isochrones it is possible to solve simultaneously for age,
  heavy-element abundance, and helium abundance. It is concluded that
  there is no correlation of globular cluster age with composition and
  that the oldest open clusters are about one-half the age of the globular
  clusters. The evidence suggests that the open clusters have a higher
  helium abundance than the globular clusters, that the globulars have
  an age of about 16.6 ± 0.5 Gyr, and that the metal-rich clusters 47
  Tuc and M71 have [Fe/H] ≡ -0.9.

Title: Convective Heating of the Inner Core in the Core Helium Flash
Authors: Cole, P. W.; Demarque, P.; Deupree, R. G.
Bibcode: 1982BAAS...14..956C
Altcode:
  No abstract at ADS

Title: Effects of a Hydrodynamic Helium Flash on Horizontal-Branch
    Evolution
Authors: Cole, P. W.; Demarque, P.
Bibcode: 1982BAAS...14R.878C
Altcode:
  No abstract at ADS

Title: The globular cluster metallicity scale - Evidence from
    stellar models
Authors: Demarque, P.; King, C. R.; Diaz, A.
Bibcode: 1982ApJ...259..154D
Altcode:
  Theoretical giant branches have been constructed to determine their
  relative positions for metallicities in the Fe/H ratio range of -2.3
  to zero. The models included the following improvements over previous
  studies: (1) in the convection zone, use of the variable mixing
  length formalism of Deupree and Varner (1980) in conjunction with
  Deupree's (1979) horizontally averaged opacity; (2) for the surface
  boundary conditions, a fit to the grid of model atmospheres of Bell
  et al. (1976). A relation between the Fe/H ratio and (B-V)o,g based
  on these models is presented which yields good agreement over the
  observed range of metallicities for galactic globular clusters and
  old disk clusters. The metallicity of 47 Tuc and M71 given by this
  calibration is about -0.8 dex.

Title: Nitrogen variations on the main sequence of 47 Tucanae -
    Implications from stellar structure theory.
Authors: Da Costa, G. S.; Demarque, P.
Bibcode: 1982ApJ...259..193D
Altcode:
  We present evolutionary calculations of a 0.9 M<SUB>sun</SUB> metal-poor
  star in which the outer layers are artificially mixed throughout the
  main-sequence lifetime. For the case where the mixed region contains
  85% of the mass of the star, evolution toward the subgiant branch is
  relatively unaffected but no significant enhancement of the surface
  nitrogen abundance occurs. Alternatively, for the case of deeper mixing,
  significant surface nitrogen enhancements are produced but the star
  evolves as a blue straggler and does not become a red giant in a normal
  way. Thus the observations of large nitrogen abundance variations among
  main-sequence stars and<SUB>giants</SUB> in the globular cluster 47
  Tuc are unlikely to be the result of deep envelope mixing on the main
  sequence. Mixing at an advanced phase of evolution and mass transfer
  in close binaries also seem unlikely. We conclude therefore that the
  most plausible explanation of the observed variations is that they are
  primordial in origin, that is, they reflect the presence of nitrogen
  abundance inhomogeneities in the protocluster gas cloud.

Title: Metal abundances and ages for some Magellanic Cloud variable
    stars.
Authors: Butler, D.; Demarque, P.; Smith, H. A.
Bibcode: 1982ApJ...257..592B
Altcode:
  The Delta-S metal abundance parameter, pulsation mass, and evolutionary
  age have been determined for 15 Magellanic Cloud field variable
  stars. It is found that the central region of the SMC is only now
  reaching the degree of chemical enrichment which the Galaxy attained
  10-billion years ago. Both the LMC and SMC contain an old, metal-poor
  population of halo stars, just as the Galaxy does. In sharp contrast
  to the case for the Galaxy, however, much of the total SMC chemical
  enrichment has taken place within the past few billion years. The
  situation for the LMC is less clear, but the data are not inconsistent
  with a chemical evolution history similar to that for the SMC.

Title: Stellar Physics. (Book Reviews: Physical Processes in Red
    Giants)
Authors: Demarque, Pierre
Bibcode: 1982Sci...216Q..46I
Altcode:
  No abstract at ADS

Title: Book-Review - Physical Processes in Red Giants - Proceedings -
    Erice Italy 1980SEP
Authors: Iben, I., Jr.; Renzini, A.; Demarque, P.
Bibcode: 1982Sci...216...46I
Altcode:
  No abstract at ADS

Title: Convection and the Thermonuclear Runaway in the Core Helium
    Flash
Authors: Cole, P. W.; Deupree, R. G.; Demarque, P.
Bibcode: 1982BAAS...14R.665C
Altcode:
  No abstract at ADS

Title: Models for Horizontal-Branch Stars with Cores Enriched in
    Carbon and Nitrogen
Authors: Demarque, P.
Bibcode: 1981apgc.conf..301D
Altcode: 1981LDP.....2..301D; 1981IAUCo..68..301D
  No abstract at ADS

Title: A Comparison of Stellar Models Constructed with Different
    Stellar Evolution Programs
Authors: Demarque, P.; Laird, J. B.; Vandenberg, D.
Bibcode: 1981apgc.conf..319D
Altcode: 1981IAUCo..68..319D; 1981LDP.....2..319D
  No abstract at ADS

Title: CH subgiants and the mixing hypothesis.
Authors: Smith, J. A.; Demarque, P.
Bibcode: 1980A&A....92..163S
Altcode:
  Some consequences of internal mixing at the helium core flash have
  been investigated for low mass, Population II stars. On the basis of
  the luminosity criterion, it seems unlikely that the internal mixing
  hypothesis can explain the CH subgiants, though it cannot be ruled
  out for the CH giants or other chemically peculiar giants. A binary
  origin for the CH subgiants is proposed.

Title: Implications of the new globular-cluster metal-abundance
    scale for the helium abundance in the Galactic halo
Authors: Demarque, P.; McClure, R. D.
Bibcode: 1980ApJ...242L...5D
Altcode:
  In the adoption of the new abundance scale for globular clusters (Cohen,
  1980; Pilachowski et al, 1980) a difficulty in fitting main sequences of
  47 Tucanae and other well-studied globular clusters, like M 3, M 5, and
  M 13 is pointed out. In order to circumvent this problem, a substantial
  difference in helium abundance must be invoked. Such differences can
  also cause the very faint turnoff magnitudes found recently by Alcaino
  and Liller (1980) for NGC 6397 and by Cannon (1974) for Omega Centauri,
  without the need to assign excessive ages to these clusters. Other
  consequences of this helium-abundance variation are discussed.

Title: Evolution of a 0.9M<SUB>⊙</SUB> with Zero Heavy Element
    Content
Authors: Demarque, P.; Guenther, D. B.
Bibcode: 1980BAAS...12..833D
Altcode:
  No abstract at ADS

Title: Metal Abundance of Magellanic Cloud Variable Stars
Authors: Butler, D.; Demarque, P.; Smith, H. A.
Bibcode: 1980BAAS...12..538B
Altcode:
  No abstract at ADS

Title: Ages and abundances of globular clusters and the oldest
    open clusters.
Authors: Demarque, P.
Bibcode: 1980IAUS...85..281D
Altcode: 1980stcl.conf..281D
  The ages and metal abundances of globular clusters and the oldest of the
  open clusters are reviewed. On the basis of a fitting of main-sequence
  turnoffs to standard theoretical isochrones, it is observed that the
  ages of well observed nearly globular clusters are between 10 and 15
  billion years, with age negatively correlated with metallicity, while
  the ages of the oldest open clusters are near 6-7 billion years and
  their metallicities are almost as low as the most metal-rich globular
  clusters. Analysis of horizontal branch morphology compared with
  stellar models indicates that all globular clusters within 5 kpc of
  the galactic center have similar ages, consistent with a rapid collapse
  and chemical enrichment, and that globular cluster further than 12 kpc
  from the center lie on or below the standard age/abundance relation
  for nearby clusters. The need for reliable abundance determinations
  for faint stars and observations of main sequence turnoffs particularly
  for distance clusters is pointed out.

Title: Stellar evolution from the zero-age main sequence.
Authors: Mengel, J. G.; Sweigart, A. V.; Demarque, P.; Gross, P. G.
Bibcode: 1979ApJS...40..733M
Altcode:
  A consistent set of 247 evolutionary sequences extending from the
  ZAMS to the red-giant branch is presented for Y from 0.10 to 0.40,
  Z from 0.00001 to 0.10, and masses of 0.55 to 6.90 solar masses. Each
  sequence is started from a homogeneous ZAMS model, and almost all
  are evolved to the base of the red-giant branch. It is shown that:
  (1) the relative position of the main sequence can be determined as
  a function of composition; (2) theoretical luminosity functions can
  be derived from the relative evolutionary time scales; (3) a dip in
  luminosity sometimes occurs at the base of the red-giant branch and is
  most pronounced at larger Z values; (4) metal-poor stars evolve farther
  up along the main sequence before turning off toward the red-giant
  branch; and (5) the onset of helium burning halts the evolution across
  the Hertzsprung gap for the most massive and most metal-poor models,
  so that the star remains blue during its phase of core-helium burning.

Title: Theoretical isochrones in the [log g - log
    T<SUB>eff</SUB>]-plane and in the [M<SUB>V</SUB>- (B-V)]-diagram.
Authors: Ciardullo, R. B.; Demarque, P.
Bibcode: 1979DudOR..14..317C
Altcode:
  No abstract at ADS

Title: The Evolution of the Integrated Colors of Globular Clusters
    and Elliptical Galaxies
Authors: Ciardullo, R. B.; Demarque, P.
Bibcode: 1978IAUS...80..345C
Altcode:
  No abstract at ADS

Title: Effects of CNO abundances on the Balmer jump of late-B
    horizontal-branch stars.
Authors: Auer, L. H.; Demarque, P.
Bibcode: 1977ApJ...216..791A
Altcode:
  Model stellar atmospheres have been constructed to investigate the
  effects of the continuous opacity of C 1, N 1, and 0 1 on the Balmer
  jump of late-B horizontal-branch stars. The large opacity of C i
  and N 1 in the ultraviolet raises the Balmer continuum through back
  warming without changing the Paschen continuum. The models provide
  a natural explanation for the variations in the Balmer jump which
  have been observed from star to star by 0ke near 12,500 K on the
  horizontal branch of the globular cluster M92. We conclude that some
  stars on the horizontal branch of M92 have an atmospheric C and/or N
  content as much as 1000 times the cluster average. Although primordial
  chemical inhomogeneities within the cluster cannot be ruled out, the
  most plausible interpretation for these objects seems to be one in
  which surface enrichment occurs through mixing from a helium-burning
  region in the interior during the course of stellar evolution. The
  possible connection with Zinn's weak G-band stars on the asymptotic
  branch of M92 is discussed. The effects of C 1 and N 1 opacities may
  also explain Newell's gap 1 in the (U - B, B - V)diagram for field blue
  stars in the halo. Subject headings: opacities - stars: atmospheres -
  stars: horizontal branch

Title: A comparison of observations with main-sequence evolutionary
    models.
Authors: Philip, A. G. D.; Demarque, P.; Sweigart, A. V.; Ciardullo,
   R. B.
Bibcode: 1977PASP...89..554P
Altcode:
  A comparison of four-color observations, transformed to the (log g -
  log ) plane, with new theoretical isochrones for the composition (Y,Z
  = 0.2, 0.04) shows good agreement between theory and observation in
  the range from 0.5 to I x i0 years. Ages are derived for seven open
  clusters which are in accord with previous estimates. Key words:
  four-color photometry-open clusters- isochrones- cluster ages

Title: The Distance Modulus of the Hyades from Stellar Models
Authors: Anthony-Twarog, B. J.; Demarque, P.
Bibcode: 1977A&A....57..471A
Altcode:
  Summary. A comparison of stellar models to observational data f6r four
  Hyades binaries is made by demanding agreement of the empirical and
  theoretical main sequences and mass-luminosity relations. A Hyades
  distance modulus of 3.34 is obtained consistent with composition
  parameters (Y; Z) (0.30,0.03). A turnoff mass of 2.1 is deduced from
  the models, implying a cluster age of5 x 108 years. Key words: Hyades -
  distance chemical composition

Title: The significance of the star clusters NGC 2420 and 47 Tucanae
    for galactic evolution.
Authors: Demarque, P.; McClure, R. D.
Bibcode: 1977ApJ...213..716D
Altcode:
  Attention is drawn to the old disk "metal-poor" cluster NGC 2420
  and the "metal-rich" globular cluster 47 Tuc, a member of the
  spheroidal component of the Galaxy, which have approximately the
  same metallicity index [8(U - B) = 0.11 mag for 47 Tuc and 8(U - B)
  = 0.10 mag for NGC 2420]. This similarity in metal abundance allows
  an instructive comparison to be made of the two components of the
  Galaxy. The color-magnitude (C-M) diagrams of the two clusters reveal
  differences which cannot be explained in terms of a difference in age
  alone. We conclude that the two clusters differ in the abundance of
  chemical elements other than those which contribute directly to the
  ultraviolet excess, i.e., either helium or the CNO elements. Comparison
  with theoretical isochrones yields agreement provided that either of
  two conditions is satisfied: (1) the helium abundance of 47 Tuc is
  greater than that of NGC 2420; or (2) the CNO content of 47 Tuc is
  less than that of NGC 2420. The implications of these alternatives
  in terms of models of galactic evolution are briefly discussed. The
  above relative fitting procedure yields a difference between the
  distance moduli of the two clusters of 1.2 mag. The difficulties in
  obtaining the absolute distance moduli are discussed. Best agreement
  is obtained for (m - M)47Tuc 13.0, corresponding to an age of about
  13 x 10 years. Subject headings: clusters: globular - clusters: open -
  stars: abundances - stars: evolution

Title: Mixing by Convective Overshoot in Population II Red Giants.
Authors: Demarque, P.; Law, W. -Y.
Bibcode: 1977BAAS....9..338D
Altcode:
  No abstract at ADS

Title: Tables of isochrones constructed from theoretical tracks of
    stellar evolution for ages between 200 and 25000 million years and
    chemical compositions in the ranges 0.1 ≤ Y ≤ 0.4 and 0.00001
    ≤ Z ≤ 0.1.
Authors: Ciardullo, Robin B.; Demarque, Pierre.
Bibcode: 1977TOYal..33....1C
Altcode:
  Star time-lines and stellar model masses calculated based from
  observations.

Title: Tables of Bolometeric Luminosity Functions, Part II. Computed
    for ages between 200 and 25000 million years, and chemical
    compositions in the ranges of 0.1≤Y≤0.4 and 0.001≤Z≤0.1
Authors: Ciardullo, Robin B.; Demarque, Pierre.
Bibcode: 1977TOYal..35....1C
Altcode:
  Data tables from observation of stars containing chemical compositions
  and bolometric luminosity functions.

Title: Sensitivity of internal structure to the surface boundary
    condition.
Authors: Demarque, P.
Bibcode: 1977saif.conf..137D
Altcode:
  No abstract at ADS

Title: Tables of bolometric luminosity functions. Part 1. Computed for
    ages between 200 and 25000 million years and chemical compositions
    in the ranges 0.1&lt;=Y&lt;=0.4 and 0.00001&lt;=Z&lt;=0.0004 Part
    2. Computed for ages between 200 and 25000 million years and chemical
    compositions in the ranges 0.1&lt;=Y&lt;=0.4 and 0.001&lt;=Z&lt;=0.1
Authors: Ciardullo, R. B.; Demarque, P.
Bibcode: 1977tblf.book.....C
Altcode:
  No abstract at ADS

Title: Tables of isochrones. Constructed from theoretical tracks
    of stellar evolution for ages between 200 and 25000 million years
    and chemical compositions in the ranges 0.1&lt;=Y&lt;=0.4 and
    0.00001&lt;=Z&lt;=0.1
Authors: Ciardullo, Robin B.; Demarque, Pierre
Bibcode: 1977tict.book.....C
Altcode:
  No abstract at ADS

Title: Stellar Populations in the Disk and Halo of the Galaxy
    (presented by R. D. McClure)
Authors: Demarque, Pierre; McClure, Robert D.
Bibcode: 1977egsp.conf..199D
Altcode:
  No abstract at ADS

Title: Tables of bolometric luminosity functions. Part I. Computed
    for ages between 200 and 25000 million years and chemical compositions
    in the ranges 0.1 ≤ Y ≤ 0.4 and 0.00001 ≤ Z ≤ 0.0004.
Authors: Ciardullo, Robin B.; Demarque, Pierre.
Bibcode: 1977TOYal..34....1C
Altcode:
  Tables from data during star observation on bolometric luminosity and
  chemical compositions.

Title: Possible Large Carbon and Nitrogen Abundance Variations on
    the Horizontal Branch of M92
Authors: Auer, L. H.; Demarque, P.
Bibcode: 1977ASSL...67...25A
Altcode: 1977cia..proc...25A
  Model stellar atmospheres have been constructed to investigate the
  effects of the continuous opacity of C I, N I, and O I on the Balmer
  jump of late-B horizontal-branch stars. The large opacity of C I and N
  I in the ultraviolet raises the Balmer continuum through back warming
  without changing the Paschen continuum, while O I has little effect. The
  models provide an explanation for the variations in the Balmer jump
  which have been observed from star to star by Oke (1975) near 12,500 K
  on the horizontal branch of the globular cluster M92. It is concluded
  that some stars in M92 appear to have an atmospheric C and/or N content
  between one hundred and one thousand times the cluster average. The same
  effect of the opacities of C I and N I may also explain Newell's (1973)
  gap N I in the (U-B)-(B-V) diagram for blue stars in the galactic halo.

Title: Possible Effects of Meridian Circulation on the Evolution of
    Low-Mass Stars
Authors: Stetson, P. B.; Demarque, P.
Bibcode: 1976BAAS....8Q.319S
Altcode:
  No abstract at ADS

Title: The Importance of NGC 2420 and 47 Tuc. for Galactic Evolution
Authors: Demarque, P.; McClure, R. D.
Bibcode: 1976BAAS....8..333D
Altcode:
  No abstract at ADS

Title: On the nature of the bright variables in dwarf spheroidal
    galaxies.
Authors: Demarque, P.; Hirshfeld, A. W.
Bibcode: 1975ApJ...202..346D
Altcode:
  Arguments are presented which suggest that the unusual 'bright
  variables' observed in Draco and other dwarf spheroidals are more
  massive than the RR Lyrae variables in the same systems. Models of
  very metal-poor stars on the horizontal branch with masses up to
  2 solar masses confirm this interpretation in the sense that both
  the luminosities and the period-luminosity relation of the models
  are consistent with the observations of the bright variables. Some
  implications of the presence of stars about one billion years old in
  dwarf spheroidal galaxies are briefly discussed.

Title: Theoretical isochrones and main sequences for old disk
    population stars.
Authors: Demarque, P.; Gisler, G. R.
Bibcode: 1975A&AS...20..237D
Altcode:
  Theoretical isochrones have been constructed for fourteen mixtures
  in the ranges of chemical compositions (0.05 &lt; Y&lt; 0.45) and
  (0.01 &lt;z &lt;0.06) and for ages relevant to the old disk population
  stars. The effects of autoionization absorption as computed by Watson
  were added to the Cox-Stewart radiative opacities. Comparison with
  the colour-magnitude diagram of M67 and NGC 188 does not favour
  supermetallicity, but rather normal abundances. Helium abundance by
  mass Yin the range of 0.25-0.35 is found. The distance of the Hyades
  cluster is discussed in terms of main sequence models extended to higher
  masses. The distance modulus is consistent with the models for a shift
  of 0.27 mag. from that given by the convergent point method. This
  shift would be smaller for lower interior opacities (i.e. if we have
  overestimated the heavy element abundance Z, or alternately if Watson's
  autoionization opacities are too large). Key words: stellar evolution -
  disk population - Hyades

Title: Models of the sun.
Authors: Demarque, P.; Mengel, J. G.; Sweigart, A. V.
Bibcode: 1975PhT....28b..71D
Altcode:
  No abstract at ADS

Title: Oblateness of solar models with rotating cores
Authors: Demarque, Pierre; Mengel, John G.; Sweigart, Allen V.
Bibcode: 1974Natur.252..368D
Altcode:
  ROOD and Ulrich<SUP>1</SUP> have discussed the oblateness of solar
  models with a rotating core. They find a larger oblateness for the same
  model than we did<SUP>2</SUP>. We have looked again into the oblateness
  calculation and now believe that the correct solution of the equations
  of Goldreich and Schubert<SUP>3</SUP> gives an oblateness for the final
  model of our<SUP>2</SUP> sequence C4 in agreement with the value derived
  by Rood and Ulrich. We also agree with Rood and Ulrich's explanation
  for the discrepancy.

Title: Convective Overshoot Mixing in Old Open Clusters .
Authors: Prather, M. J.; Demarque, P.
Bibcode: 1974ApJ...193..109P
Altcode:
  A simplified form of overshoot mixing of convective cores in
  intermediate-mass stars (0. .40 o) is investigated in order to explain
  the anomalous gap structure of M67. The amount of overshooting
  is assumed to be proportional to the pressure scale height at
  the convective core boundary, and the entire region is completely
  mixed. Evolutionary tracks are computed for both standard and overshoot
  models, and isochrones are constructed. in the presence of overshoot
  mixing, the isochrones show (1) a higher gap, (2) a lower stellar
  number density immediately above the gap, and (3) the persistence of
  the gap to greater ages. Subject headings: convection - interiors,
  stellar - open clusters - stellar evolution

Title: Helium Inhomogeneities and the Solar Neutrino Problem
Authors: Demarque, P.; Mengel, J. G.; Sweigart, A. V.
Bibcode: 1974BAAS....6..271D
Altcode:
  No abstract at ADS

Title: Erratum: Rotating Solar Models with Low Neutrino Flux
Authors: Demarque, Pierre; Mengel, John G.; Sweigart, Allen V.
Bibcode: 1974ApJ...187..423D
Altcode:
  No abstract at ADS

Title: Yale University Observatory, New Haven,
    Connecticut. Observatory report.
Authors: Demarque, P.
Bibcode: 1974BAAS....6..199D
Altcode:
  No abstract at ADS

Title: Variable Stars and Evolution in Globular Clusters
Authors: Demarque, P.
Bibcode: 1974IAUS...59..105D
Altcode:
  No abstract at ADS

Title: On the Origin of the Blue Halo Stars
Authors: Sweigart, A. V.; Mengel, J. G.; Demarque, P.
Bibcode: 1974A&A....30...13S
Altcode:
  Summary. The existence in the halo population of UV-bright stars
  lying above the horizontal branch in luminosity and blueward of the
  asymptotic branch is interpreted in terms of the final evolution
  of three stars with masses of 0.453, 0.51 and 0.60 M0. These stars,
  representing different possible evolutionary patterns, are consistent
  with observations of high-luminosity and subdwarf 0 stars. In addition
  the 0.51 M0 star provides a satisfactory explanation of the supra
  horizontal-branch stars. The stars of 0.51 and 0.60 M0 undergo a series
  of helium-shell flashes, leading to large and rapid excursions in the
  HR diagram. The present computations cannot account for the subdwarf
  B stars. Difficulties associated with several interpretations of the
  subdwarf B stars are discussed. Key words: shell flashes - halo stars -
  supra-horizontalbranch stars - subdwarf B stars - subdwarf 0 stars

Title: Solar Rotation and the Neutrino Flux
Authors: Demarque, P.; Mengel, J. G.; Sweigart, A. V.
Bibcode: 1973NPhS..246...33D
Altcode: 1973Natur.246...33D
  Some possible mechanisms for producing a low neutrino flux from solar
  models are discussed. Rapid internal rotation is shown to reduce the
  predicted neutrino flux to the upper limit observed by Davis.

Title: Possible Effects of Internal Rotation on Population II Stars.
Authors: Demarque, P.; Gross, P. G.; Mengel, J. G.
Bibcode: 1973BAAS....5..406D
Altcode:
  No abstract at ADS

Title: The Effect of Overshoot Mixing in Old Galactic Clusters.
Authors: Prather, M. J.; Demarque, P.
Bibcode: 1973BAAS....5..405P
Altcode:
  No abstract at ADS

Title: Rotating Solar Models with Low Neutrino Flux
Authors: Demarque, Pierre; Mengel, John G.; Sweigart, Allen V.
Bibcode: 1973ApJ...183..997D
Altcode:
  The effect of rotation on the structure of the Sun throughout its
  evolution has been investigated in an effort to explain the low upper
  limit to the solar neutrino flux measured by Davis. A class of models
  has been found which produce a predicted neutrino capture rate in the
  vicinity of 1 SNU. Such models are characterized by a rotating interior
  which contains initially 0.9 M0 and which is progressively spun down
  until a rotating remnant core of the order of 0.1 M0. remains in
  the present Sun. The dependence of the neutrino flux on the mass in
  the remnant rotating core, the degree of rotation, the assumed law
  of spindown, and the mixing produced by meridional circulation have
  been investigated. Finally the oblateness of each rotating model has
  been calculated. Subject headings: interiors, solar - neutrinos -
  rotation, solar

Title: Rotating Solar Models with Low Neutrino Flux.
Authors: Demarque, P.; Mengel, J. G.; Sweigart, A. V.
Bibcode: 1973BAAS....5..313D
Altcode:
  No abstract at ADS

Title: Do helium inhomogeneities resolve the solar neutrino problem?
Authors: Demarque, P.; Mengel, J. G.; Sweigart, A. V.
Bibcode: 1973MNRAS.165P..19D
Altcode:
  Detailed solar models do not support the conclusion of Prentice that
  the presence of a hydrogen-free core can greatly reduce the neutrino
  flux from the Sun.

Title: Nitrogen enrichment due to meridional circulation in main
    sequence stars
Authors: Demarque, Pierre; McClure, Robert D.
Bibcode: 1973MNRAS.164P...5D
Altcode:
  Paczyhski has presented arguments in support of the idea that rotating
  mainsequence stars in the mass range 2-10 M0 should show evidence
  for carbon depletion and nitrogen enrichment in their envelopes. An
  attempt to test this theory in terms of the relative CN-strength of
  K-giant stars tends to support Paczyn'ski's suggestion.

Title: Semiconvection and the RR Lyrae Variables
Authors: Sweigart, A. V.; Demarque, P.
Bibcode: 1973ASSL...36..221S
Altcode: 1973IAUCo..21..221S; 1973vsgc.coll..221S
  No abstract at ADS

Title: Evolution from the Main Sequence to the Helium Flash for
    Population II Stars
Authors: Demarque, P.; Mengel, J. G.
Bibcode: 1973A&A....22..121D
Altcode:
  Summary. Evolutionary turnoffs from the main sequence for stars of
  low mass with the composition parameters 0.50&gt; Y&gt; 0 and Z= t0-
  and t0- are presented and compared with previous results. The evolution
  of red giants to the helium flash is also investigated in an attempt
  to determine more reliably: (a) the effect of chemical composition
  on the position and slope of the giant branch; (b) the dependence on
  the original value of Y of the core mass and maximum luminosity at
  the helium flash; (c) the dependence of red-giant lifetimes on the
  total mass of the star. The position and extent of the luminosity
  dip discovered by Thomas (1967) is also briefly discussed. Key words:
  stellar evolution - red giants - globular clusters - population II stars

Title: Variable Stars and Evolution in Globular Clusters (review
    Paper)
Authors: Demarque, P.
Bibcode: 1973ASSL...36..187D
Altcode: 1973vsgc.coll..187D; 1973IAUCo..21..187D
  No abstract at ADS

Title: Remarks on stellar abundances.
Authors: Demarque, P.
Bibcode: 1973stag.conf...21D
Altcode: 1973IAUCo..17...21D
  No abstract at ADS

Title: Yale University Observatory, New Haven,
    Connecticut. Observatory report.
Authors: Demarque, P.
Bibcode: 1973BAAS....5..258D
Altcode:
  No abstract at ADS

Title: The R-Method for Determining the Helium Abundance of Globular
    Clusters
Authors: Demarque, P.; Sweigart, A. V.; Gross, P. G.
Bibcode: 1972NPhS..239...85D
Altcode: 1972Natur.239...85D
  ON the basis of calculations of evolution of Population
  II stars, Iben<SUB>1</SUB> has shown that the ratio R of
  theoretical horizontal branch (HB) to red giant (RG) lifetimes
  (R = t<SUB>HB</SUB>/t<SUB>RG</SUB>) is a function of their helium
  abundance. This ratio can also be written where N<SUB>HB</SUB> and
  N<SUB>RG</SUB> represent the number of the two kinds of stars in an
  individual globular cluster. Number counts can then be used to estimate
  the helium abundance of the cluster. With the help of a theoretical
  calibration<SUP>2</SUP>, Iben et al.<SUP>3</SUP> then determined the
  helium content of a number of globular clusters for which observations
  were available<SUP>4, 5</SUP>. They found an average value, R~=0.9,
  which yielded y~=0.27-0.31, a result in good agreement with other
  estimates of helium abundance in globular clusters.

Title: Population II Stars and the Electron-Neutrino Weak Interaction
Authors: Demarque, P.; Mengel, J. G.
Bibcode: 1972NPhS..239...55D
Altcode: 1972Natur.239...55D
  The theory of Feynman and Gell-Mann<SUP>1</SUP> of weak interactions
  predicts an electron-neutrino interaction (\emacr v<SUB>e</SUB>)
  (\vmacr<SUB>2</SUB> e) with the same coupling constant as that measured
  in β-decays. Owing to the lack of experimental verification of this
  prediction, a number of investigators have searched for possible
  astrophysical tests of the theory. The interaction cross-section
  of neutrinos with matter is very low and cosmic neutrinos are
  extremely difficult to detect directly. For this reason, however,
  they will escape unimpeded from stars and if produced in large
  quantities in stellar interiors, can have a marked effect on the total
  energy budget of some stars and consequently on their evolutionary
  time-scales. Ruderman<SUP>2</SUP> and Chiu<SUP>3</SUP> have discussed
  various aspects of this problem. Stothers<SUP>4</SUP> has reviewed
  the relevant astrophysical data and concluded that so far all evidence
  confirms the existence of the interaction. He further concluded that
  g<SUP>2</SUP>=g<SUP>2</SUP><SUB>β</SUB> × 10°<SUP>+/-2</SUP>,
  where g<SUB>β</SUB> is the β-decay coupling constant.

Title: Effects of Semiconvection on the Horizontal-Branch
Authors: Sweigart, A. V.; Demarque, P.
Bibcode: 1972A&A....20..445S
Altcode:
  Summary. The effects of semiconvection on the horizontal-branch
  evolution of a 0.60 M0 Population II star with the envelope composition
  parameters X =0.732 and Z =0.001 are investigated. Following an initial
  phase of convective-core overshooting the models form a semiconvective
  zone which at its maximum extent results in the depletion of helium
  out to a mass value of 0.25 M0. A comparison between sequences
  computed with and without a treatment of semiconvection indicates
  that the neglect of semiconvection will (a) reduce the length of
  the horizontal-branch track by a factor of 1.8 and (b) decrease the
  horizontalbranch lifetime by a factor of 1.9. A number of additional
  horizontal-branch sequences including a treatment of semiconvection
  are presented over the mass range from 0.51-0.65 M0. These sequences
  suggest that a mass spread on the order of 0.05 M0 would be sufficient
  to produce a dispersion of 0.30 in log Teff over the log Teff interval
  from roughly 3.70-4.15. Key words: stellar evolution - semiconvection -
  honzontal-branch - Population II stars

Title: Theoretical Isochrones for Disk Population Stars.
Authors: Demarque, P.; Gisler, G.
Bibcode: 1972BAAS....4..326D
Altcode:
  No abstract at ADS

Title: Some Uncertainties on Models for Horizontal-Branch Stars
    (These papers are represented by abstracts)
Authors: Demarque, Pierre; Mengel, John G.
Bibcode: 1972teps.proc...27D
Altcode:
  No abstract at ADS

Title: A Possible Explanation of the Gaps on the Giant Branch of M15
Authors: Demarque, Pierre; Mengel, John G.; Sweigart, Allen V.
Bibcode: 1972ApJ...173L..27D
Altcode:
  It is conlectured that fast rotating cores in the red giants of MIS
  might explain the possible existence of gaps on the giant branch of
  the cluster. In going outward through the transition layer between the
  rotating core and the nonrotating envelope the temperature gradient
  dT/dr will increase abruptly. As the hydrogen-burning shell traverses
  this transition layer, a sudden increase in the luminosity might
  therefore be expected. A numerical simulation of this phenomenon has
  confirmed this prediction. Some implications of this hypothesis on
  the evolution of Population II stars are briefly discussed.

Title: Advanced Evolution of Population II Stars. III. Some
    Uncertainties in Horizontal-Branch Models
Authors: Demarque, Pierre; Mengel, John G.
Bibcode: 1972ApJ...171..583D
Altcode:
  Evolution from the zero-age horizontal branch is investigated for
  stars with the chemical composition parameters (X, Z) = (0.75,
  10- ) and masses 0.50, 0.56, and 0.60 M0. For the 0.60 M0 models,
  the effects of semiconvection and of the, choice of interpolation
  between opacity tables are studied. It is found that increasing the
  free-free opacities in the region enriched in carbon and oxygen affects
  the evolution markedly, yielding longer blue loops and a horizontal
  branch thicker in luminosity. Semiconvection, which has the effect of
  increasing the size of the convective core and of forming an extensive
  region of varying chemical composition, also leads to longer blueward
  loops and longer times spent on the horizontal branch as opposed to
  the asymptotic branch. Astronomical implications are briefly discussed.

Title: Yale University Observatory, New Haven,
    Connecticut. Observatory report.
Authors: Demarque, P.
Bibcode: 1972BAAS....4..202D
Altcode:
  No abstract at ADS

Title: Concluding Remarks
Authors: Demarque, P.
Bibcode: 1972ade..coll...21D
Altcode: 1972IAUCo..17...21D
  No abstract at ADS

Title: Evolution Near the Main Sequence
Authors: Demarque, P.
Bibcode: 1972stev.conf..107D
Altcode:
  No abstract at ADS

Title: Effects of Semi-convection on the Horizontal Branch.
Authors: Demarque, P.; Sweigart, A.
Bibcode: 1971BAAS....3..479D
Altcode:
  No abstract at ADS

Title: Is There a Black Hole in ɛ Aurigae?
Authors: Demarque, Pierre
Bibcode: 1971Natur.230..516D
Altcode:
  THE suggestion has been made<SUP>1,2</SUP> that the secondary
  component of the eclipsing binary system ɛ Aurigae is a black hole,
  the result of a stellar implosion. Current interest in the physics of
  black holes<SUP>3</SUP> and the research by Wilson<SUP>4</SUP> on the
  dynamics of the supernova phenomenon, which indicates that collapsed
  objects may be quite common in the galaxy, make Cameron's<SUP>1</SUP>
  suggestion particularly intriguing.

Title: Advanced Evolution of Population II Stars. I. Red Giants and
    the Helium Flash
Authors: Demarque, Pierre; Mengel, John G.
Bibcode: 1971ApJ...164..317D
Altcode:
  Models for red-giant stars of Population II have been constructed with
  emphasis on the determination of the critical mass of the helium core
  at the onset of the helium flash and on the subsequent development
  of the flash and core-cooling phase which precedes horixontal-branch
  evolution. Stars with masses 0.85, 0.60, and 0.502 and compositions
  (X, Z) = (0.75, 0.001) and (0.75, 0.0001) have been considered. The
  effects of including relativistic degeneracy have been investigated,
  together with the effects of the inclusion of neutrino losses due to
  weakAnteraction processes. No mixing between the helium core and the
  hydrogen-rich envelope is found in any of the models considered. The
  dependence of the mass of the helium core on total mass and on Z has
  been determined and found to be very weak in both cases. Finally,
  a tentative explanation for Barnard 29 is suggested.

Title: Advanced Evolution of Population II Stars. II. The Horizontal
    Branch
Authors: Demarque, Pierre; Mengel, John G.
Bibcode: 1971ApJ...164..469D
Altcode:
  Evolutionary tracks for post-helium-flash and horizontal-branch
  evolution are presented for masses 0.85,0.60,0.559, and 0.502 . The
  surface chemical composition is (X, Z) = (0.733,0.001) corresponding to
  (X, Z) = (0.75, 0.001) on the main sequence. Comparison with Newell's
  study of blue horizontalbranch stars yields agreement with his Group
  A for 0.60 . The very blue stars in Newell's Groups B and C, so far
  unexplained, are seen to have masses ranging from 0.50 to 0.56 . Mass
  loss and other less likely explanations of the low masses found are
  briefly discussed.

Title: A Method for the Simultaneous Determination of Helium and
    Metal Abundances in Old Open Clusters
Authors: Demarque, Pierre; Heasley, James N., Jr.
Bibcode: 1971ApJ...163..547D
Altcode:
  A method for the simultaneous determination of the helium content V,
  and metal content Z, for stars in old open clusters is described. The
  method is independent of the distance modulus of the cluster and of
  color corrections. It is found that the maximum luminosity during the
  phase of evolution in which hydrogen is burned in a thick shell is
  proportional to V for fixed Z. By using this effect and the analysis
  of the dependence of the gap width upon V for fixed Z determined by
  Aizenman, Demarque, and Miller it is possible in principle to determine
  V and Z for an old open cluster. In order to calibrate this new effect
  a series of theoretical evolutionary tracks was computed for stars
  evolving from the main sequence to the base of the giant branch for
  different chemical compositions. Problems of observational comparison
  are considered.

Title: Yale University Observatory, New Haven,
    Connecticut. Observatory report.
Authors: Demarque, P.
Bibcode: 1971BAAS....3..432D
Altcode:
  No abstract at ADS

Title: The Early Evolution of Population II Stars. II
Authors: Demarque, Pierre; Mengel, John G.; Aizenman, Morris L.
Bibcode: 1971ApJ...163...37D
Altcode:
  Evolutionary tracks for Population II stars of low mass are
  presented. The chemical composition lie: in the range 0.50 &lt;
  X &lt;0.999 and 10- &lt;Z &lt; 10- . Isochrones suitable for
  comparison with color magnitude diagrams of globular clusters have been
  constructed. The results are compared with earlie work, in particular
  with models by Simoda and Iben and Iben and Rood. Discrepancies are
  everywber less than 12 percent, except for the stellar radii which
  are subject to larger uncertainties due to th hydrogen convection
  zones. The strong dependence on Z of the turnoff luminosity for very
  low Z foun by Simoda and Iben is confirmed qualitatively.

Title: Red giant evolution to the heliumflash of a super-metal-rich
    star
Authors: Demarque, Pierre; Heasley, James N.
Bibcode: 1971MNRAS.155...85D
Altcode:
  An evolutionary sequence is presented for a star of 1 19 M , with
  composition parameters (X, Z) = ( , ). The evolution was followed
  from the main sequence to the onset of convection in the core during
  the helium flash. The resulting core mass at the helium flash, Me =
  M is smaller than those found for Population II stars with the same
  helium abundance. No mixing between hydrogen-rich envelope and the
  helium core can be expected due to the non-central development of the
  flash. The clumping of stars on the giant branch of old open clusters,
  discussed by Cannon, is considered.

Title: A Method for the Simultaneous Determination of Helium and
    Metal Abundances in Old Galactic Clusters
Authors: Demarque, Pierre; Heasley, James N., Jr.
Bibcode: 1970BAAS....2Q.308D
Altcode:
  No abstract at ADS

Title: Early Evolution of Population II Stars
Authors: Demarque, Pierre; Mengel, John G.
Bibcode: 1970BAAS....2R.308D
Altcode:
  No abstract at ADS

Title: Stellar Evolution through the Helium Flash
Authors: Demarque, Pierre; Mengel, John G.
Bibcode: 1970BAAS....2S.308D
Altcode:
  No abstract at ADS

Title: Yale University Observatory, New Haven, Connecticut. Report
    1968-1969.
Authors: Demarque, P.
Bibcode: 1970BAAS....2..166D
Altcode:
  No abstract at ADS

Title: ON the Color-Magnitude Diagrams of NGC 2360 and NGC 3680
Authors: Demarque, Pierre; Miller, Richard H.
Bibcode: 1969ApJ...158.1037D
Altcode:
  Eggen's recent observations of the color-magnitude diagrams of the two
  galactic clusters NGC 2360 and NGC 3680 are interpreted by the method
  previously applied to M67 and NGC 188 The width of the gap in NGC 2360
  is the same as that in M67, implying similar chemical composition. The
  gap in NGC 3680 is significantly wider, suggesting a much higher helium
  abundance. NGC 3680 may be a `super-metal-rich" cluster

Title: ON the Chemical Composition and Age of NGC 188
Authors: Demarque, Pierre; Schlesinger, Barry M.
Bibcode: 1969ApJ...155..965D
Altcode:
  Stellar models for a wide range of chemical compositions are constructed
  in an attempt to explain the presence of a gap above the main sequence
  in the C-M diagram of NGC 188. The procedure of fitting the theory to
  the observations is described. Agreement with observation is obtained
  for a high value of the metal content, Z ~ 0.07. The corresponding
  age for the cluster is of the order of 7 X 1O~ years

Title: ON the Interpretation of the Color-Magnitude Diagrams of M67
    and NGC 188
Authors: Aizenman, Morris L.; Demarque, Pierre; Miller, R. H.
Bibcode: 1969ApJ...155..973A
Altcode:
  A method for determining the helium content Y, for a given Z, of old
  galactic clusters is described. This method could be of considerable
  importance since it is independent of the distance modulus of the
  cluster and of color corrections such as those due to interstellar
  reddening and differential line blanketing. It is found that V is
  proportional to the width of the gap of the C-M diagram just above the
  main sequence In order to calibrate this effect, a number of theoretical
  evolutionary tracks was obtained from the main sequence to beyond the
  hydrogen-exhaustion phase for different chemical compositions. A sta-
  tistical analysis of the data of Eggen and Sandage was made which
  confirms the presence of such a gap in M67 and NGC 188 It shows that
  the gap width has a well-defined value equal to 0.167 Â± 0.010 mag
  in M67. This last result yields V = 038 Â± 0.02 at Z = 0 03 and V =
  0.28 Â± 0.02 at Z = 0.06. Higher V-values would be required if Z
  is as low as 001. The corresponding ages for M67 are about 3.5 X 1O~
  years for V = 0.38, Z = 0.03, and 2 6 X 1O~ years for V = 0 28, Z =
  0.06. In NGC 188, the gap, al- though present, does not appear to
  be fully developed, which leaves some uncertainty as to its chemical
  composition if this method is used

Title: Some Uncertainties in Population II Stellar Models Near the
    Main Sequence
Authors: Demarque, Pierre; Hartwick, F. D. A.; Naylor, M. D. T.
Bibcode: 1968ApJ...154.1143D
Altcode:
  Stellar models for Population II stars near the main sequence, computed
  in several different ways, are compared. It is found that, although
  there are considerable uncertainties in the radii of such models,
  the bolometric magnitude is nearly constant for a given age, mass,
  and chemical composition

Title: Some Current Problems in the Theory of Late-Type Stars
Authors: Demarque, Pierre
Bibcode: 1968AJ.....73..669D
Altcode:
  Present uncertainties in the position of the main sequence for
  Population I and Population II stars, and in the ages and chemical
  composition of old galactic clusters and globular clusters are discussed
  in terms of galactic evolution and current views in cosmology.

Title: Interpretation of the C-M Diagrams of M67 and NGC 188
Authors: Aizenman, Morris L.; Demarque, Pierre; Miller, R. H.
Bibcode: 1968AJS....73S.161A
Altcode:
  A method for determining the helium content Y, for a given Z, of
  old galactic clusters is described. This method is independent of
  differential line blanketing and interstellar reddening. It is found
  that Y is proportional to the width of the gap of the C-M diagram
  just above the main sequence. In order to calibrate this effect, a
  number of theoretical evolutionary tracks was obtained from the main
  sequence to beyond the hydrogen exhaustion phase for different chemical
  compositions. A statistical analysis of the data of Eggen and Sandage
  (1964) was made which confirms the presence of such a gap in M67 and
  NGC 188 It shows that the gap width has a well-defined value equal to
  0.167~0.010 mag in M67. This last result yields Y=0.38~0.02 atZ=0.03
  and Y=0.28~0.02 at Z=0.06. Higher Y values would be required if Z is
  as low as 0.01. The corresponding ages for M67 are about 3.5X109 yr for
  Y=0.38, Z=0.03, and 2.6X109 yr for Y=0.28, Z=0.06. In NGC 188, the gap,
  although present does not appear to be fully developed, leaving some
  uncertainty as to its chemical composition if this method is used.

Title: The Distance Modulus of Hyades: Distances in the Universe
    and Stellar Interiors
Authors: Demarque, Pierre
Bibcode: 1967ApJ...150..943D
Altcode:
  It is shown that Hodge and Wallerstein's recent suggestion of a
  revision in the Hyades distance modulus does not remove the difficulties
  previously encountered by Iben and Bodenheimer in comparing the Hyades
  binaries with stellar interior models The problem seems to lie with
  the individual parallaxes attributed to each binary system It is also
  pointed out that a change in the Hyades distance modulus would not
  necessarily affect other distances in the Universe.

Title: Dependence of the ^8{B} Solar Neutrino Flux on Heavy Element
    Composition
Authors: Bahcall, John N.; Cooper, Martin; Demarque, Pierre
Bibcode: 1967ApJ...150..723B
Altcode:
  No abstract at ADS

Title: Hyades Distance Modulus and Stellar Interiors.
Authors: Demarque, Pierre
Bibcode: 1967AJ.....72S.792D
Altcode:
  It is shown that Hodge and Wallerstein's recent suggestion
  (Publ. Astron. Soc. Pacgic 78, 411,1966) of a revision in the
  Hyades distance modulus does not remove the difficulties previously
  encountered by Iben (Astrophys. J. 138, 452,1963) and Bodenheimer
  (Astrophys. J. 142, 451,1965) in comparing the Hyades binaries with
  stellar interior models. The problem seems to lie with the individual
  parallaxes attributed to each binary sytsem. It is also pointed out
  that a change in the Hyades distance modulus would not necessarily
  affect other distances in the universe.

Title: The Early Evolution of Population II Stars
Authors: Demarque, Pierre
Bibcode: 1967ApJ...149..117D
Altcode:
  Results of calculations of stellar evolution from the main sequence are
  presented for a range of masses and chemical compositions applicable to
  subdwarfs and globular-cluster members Twenty-two evolutionary tracks
  consisting of more than 770 models were obtained for the following
  compositions X = 0 999, 0 90, and 0 75 for Z = 0001 and X = 0 99 and
  0.76 for Z = 0 01. These tracks were used to construct isochrones in the
  M i4og Teff diagram. It is emphasized that observed subdwarfs should
  not be compared with main-sequence models but rather with isochrones
  corresponding to their age and chemical composition. The slope of
  the observational data then favors a "normal" helium abundance Other
  evidence, however, suggests the possibility of variations in helium
  content from one Population II object to another. Uncertainties in
  the radii of the stellar models in this region of the H-R diagram
  are discussed, and it appears that the only fully reliable coordinate
  in the H-R diagram to be obtained from the theory is the value of at
  the turnoff point. No gap above the turnoff point similar to the one
  observed in M67 and confirmed by Population I models is predicted in
  globular-cluster color-magnitude arrays.

Title: Hydrogen Convection Zones and Stellar Rotation
Authors: Demarque, P.; Roeder, R. C.
Bibcode: 1967ApJ...147.1188D
Altcode:
  No abstract at ADS

Title: The Hydrogen and Helium Content of Extreme Population i Objects
Authors: Percy, John R.; Demarque, P. R.
Bibcode: 1967ApJ...147.1200P
Altcode:
  No abstract at ADS

Title: The Early Evolution of a Star of 1.2 Solar Masses
Authors: Hallgren, E. L.; Demarque, P. R.
Bibcode: 1966ApJ...146..430H
Altcode:
  Evolutionary models for a star of 1.2 Mo are constructed. The initial
  composition is X = 0.67 and Z = 0.03 with a mixing length equal to
  the pressure scale height. The star is evolved through the stages of
  hydrogen depletion, gravitational contraction, burning of the shell
  source, and a second gravitational contraction. The evolutionary track,
  in its main features, is found to be more similar to that of a 2.0 Mo
  star than to that of a 1.0 Mo star.

Title: Solar Evolution and Brans-Dicke Cosmology
Authors: Roeder, R. C.; Demarque, P. R.
Bibcode: 1966ApJ...144.1016R
Altcode:
  The evolution of the Sun from the zero-age main sequence has been
  studied using the assumption that the gravitational constant, G,
  is time-dependent and is given by the flat-space solution of the
  Brans-Dicke theory. The effects of the choice of the parameters co
  and H upon the evolutionary track are shown. It is concluded that
  a good fit to the present Sun in terms of Mbel and log Teff can be
  found for reasonable choices of the above parameters and chemical
  composition. The results obtained here also imply that the neutrino
  flux from the Sun could be appreciably different from that predicted
  by Ezer and Cameron without conflicting with the Brans-Dicke theory.

Title: Evolution of Stars Near One Solar Mass
Authors: Demarque, P.
Bibcode: 1966stev.conf..231D
Altcode:
  No abstract at ADS

Title: The Upper Main Sequence
Authors: Morris, Stephen C.; Demarque, Pierre
Bibcode: 1966ZA.....64..238M
Altcode:
  No abstract at ADS

Title: On Fernie's Period-Radius Mass Relation for Variable Stars.
Authors: Demarque, Pierre; Percy, Jojn R.
Bibcode: 1965ApJ...142.1082D
Altcode:
  A counterpart to Fernie's period-radius-mass relation for variable
  stars is obtained applying the classical theory of adiabatic pulsation
  to models for giant stars. The expression, which is to be regarded
  as approximate, is based on models with masses ranging from 1.2 to
  20 solar masses. No attempt was made to study the physical processes
  responsible for the pulsation.

Title: The Evolutionary Status of β Cephei Stars.
Authors: Demarque, Pierre; Percy, John R.
Bibcode: 1965AJ.....70S.136D
Altcode:
  Use is made of the evolutionary tracks for stars of 10.1 and 15. SM
  presented at this Meeting by Demarque, Morris, and Percy. Following
  Schmalberger (Astrophys. J. 132, 591, 1960), the coincidence in the H-R
  diagram of the phase of hydrogen exhaustion in the core and the position
  of the p Cephei stars is emphasized. The effective ratio of specific
  heats in our models is found to be close to but somewhat below the
  value of 1.6 found by Chandrasekhar and Lebovitz (Astrophys. J. 136,
  1105, 1962) to explain the nonradial pulsation models of p Canis
  Majoris. Changes in the period of adiabatic pulsation with time are
  also investigated and compared with observation.

Title: Solar Evolution and Cosmology.
Authors: Roeder, R. C.; Demarque, P. R.
Bibcode: 1965AJ.....70S.689R
Altcode:
  Investigations of solar evolution in the flat space model universe
  of Brans and Dicke [where the gravitational constant is a function of
  epoch given by G=G0(t0/t)n, n=2/(4+3co)] have been carried out for ~=4,
  6, 8, and a Hubble constant of 75 and 100 km/sec/Mpc. Evolutionary
  tracks covering an interval of 4.5 x 1 0~ yr have been calculated
  using Larson and Demarque's version (Astrophys. J. 140, 524, 1964) of
  the Henyey method for various solar compositions having Z--0.03. The
  results show that the effect of increasing is to change the shape of the
  evolutionary track in the H-R diagram from a steep downward line-similar
  to that found by Pochoda and Schwarzschild (Astrophys. J. 139, 587,
  1964) for co=2-tO a U-shaped curve and ultimately (as co~ co) to the
  conventional upward curve. It also appears that increasing the Hubble
  constant from 75 to 100 km/sec/Mpc makes relatively little difference
  in the composition needed to fit the present sun, but has a drastic
  effect on the shape of the evolutionary track.

Title: Main Sequence and Early Evolutionary Models for Moderately
    Massive Stars.
Authors: Morris, Stephen C.; Demarque, Pierre; Percy, John R.
Bibcode: 1965AJ.....70Q.145M
Altcode:
  Main sequence models have been constructed for stars of composition
  X=0.67, Z=0.03, with masses ranging from 1.4 to 15.9 solar masses. The
  method used is that described by Larson and Demarque (Larson, R. B.,
  and Demarque, P. R., Astrophys. J. 140, 524, 1964), modified to allow
  for radiation pressure. The energy source is hydrogen burning, using the
  formulas given by Reeves (Reeves, H., Stellar Energy Sources, Institute
  for Space Studies Preprint). The opacity law used is a Kramers'type
  formula plus electron scattering, the latter being dominant for more
  massive stars. Radiative zero boundary conditions are assumed. The
  resulting models have been compared with the observed mass-luminosity
  relation and with the zero- age main sequence, after transforming
  M1101, log Te to Mv, (B - V). The agreement is entirely satisfactory,
  considering the uncertainties in the transformation. Models of 10.1
  and 15.5 solar masses have been evolved to the stage of core exhaustion
  of hydrogen. Evolution proceeds in the direction of increasing Mv and
  (B- V) until core exhaustion is approached; then (B- V) decreases
  again, while Mv decreases slightly. This turning point is reached
  in 17.6 and 10.2 million years for stars of 10.1 and 15.5 solar
  masses, respectively. A comparison has been made with an evolutionary
  track calculated for a star of 15.6 solar masses, with X=.90, Z=.02
  (Sakashita, S., Ono, Y., and Hayashi, C., Progr. Theoret. Phys. 21,
  315,1959; Hayashi, C., and Cameron, R. C., Astrophys. J. 136, 166,
  1962). The shape of this track compares well with that of our star of
  15.5 solar masses, but the positions in the color-magnitude diagram
  and the evolutionary time scales are different, as is expected, owing
  to the different chemical compositions.

Title: An Application of Henyey's Approach to the Integration of
    the Equations of Stellar Structure.
Authors: Larson, R. B.; Demarque, P. R.
Bibcode: 1964ApJ...140..524L
Altcode:
  A method is described for the numerical solution of the equations of
  stellar structure by a technique especially designed for the solution
  of boundary-value problems. The numerical solution incorporates the
  boundary conditions from the start and eliminates the necessity
  for the trial-and-error calculations involved in many previous
  methods. Model-atmosphere calculations and mixing-length theory can
  readily be incorporated for accurate treatment of convective envelopes,
  and the method is capable of treating more or less exactly the energy
  generation and opacity laws and the equation of state for partial
  degeneracy. In addition, the method is well suited for the computation
  of evolutionary sequences of models. The method has been successfully
  used at the University of Toronto for a number of purposes, including
  the computation of evolutionary tracks from the main sequence for the
  purpose of estimating the ages of old star clusters.

Title: A Series of Solar Models.
Authors: Demarque, P. R.; Percy, J. R.
Bibcode: 1964ApJ...140..541D
Altcode:
  Models for the Sun are constructed, assuming a solar age between 4 5
  and 5 X 10' years, and the hydrogen content corresponding to metal
  abundances between Z = 0 02 and Z = 0.04 are determined The mixing
  length yielding the present solar radius is also determined in terms
  of the pressure-scale height in the outer convection zone.

Title: The Age of Galactic Cluster NGC 188.
Authors: Demarque, P. R.; Larson, R. B.
Bibcode: 1964ApJ...140..544D
Altcode:
  The early evolution of lower main-sequence stars of Population I
  (composition parameters X = 0.67, Z = 0.03) is calculated on an IBM 7090
  computer using the entirely automatic method of Larson and Demarque
  (1964). The agreement between theory and Sandage's color-maguitude
  diagram of NGC 188 is good and yields an age of 9- 10 X 10' years for
  that cluster. From another evolutionary track for X = 0 75 and Z = 0.01,
  the age of NGC 188 is estimated at 12 X 10' years, but it is found in
  this case that agreement with observation is not as satisfactory as
  for composition (X = 0 67, Z = 003).

Title: Ages of Old Clusters.
Authors: Demarque, P. R.; Larson, R. B.
Bibcode: 1964AJ.....69R.136D
Altcode:
  The ages of old star clusters are determined from theoretical
  evolutionary tracks for stars around one solar mass, using a method
  similar to that of Henyey et al. (Astrophys. J. 129, 628,1959). For a
  given mass and composition, the calculations, performed with the IBM
  7090 of the University of Toronto, are entirely automatic, including
  the construction of the hydrogen convection zone on the outside. The
  age of the old Population I star cluster NGC 188 is found to be
  between 9 and lOX 10~ yr, under the assumption that X =0.67 and Z
  =0.03. Population II stars, for which Z = 0.001, have an uncertain
  hydrogen content and calculations were performed for X=0.999, X=0.90
  and X=0.75, yielding corresponding ages for the globular clusters M3,
  MS, M13 between approximately 25X109 and 17X109 yr.

Title: Models for Red Giant Stars. I.
Authors: Demarque, Pierre; Geisler, John E.
Bibcode: 1963ApJ...137.1102D
Altcode:
  The evolution of population II stars into the red giant region of
  the H-R diagram is investigated, with a series of quasi-stationary
  models. The main features of the models are the following: a) The
  central region forms an isothermal partially degenerate core of
  helium. Both the pressure of the partially degenerate electrons and
  that of the non-degenerate nuclei are taken into account. The mass of
  the helium core increases as the star evolves b) The energy generation
  is principally due to the carbon-nitrogen cycle. Also included are
  the proton- proton chains through He3(He3, 2p)He4 and He3(a, )Be7(
  -, p)Li7(p, He4. Both C-N cycle and p-p chains are concentrated
  in a shell surrounding the helium core of the star. c) The opacity
  calculations of Keller and Meyerott are used. d) The outer boundary
  conditions are obtained from a gray model atmosphere. The structure
  of the convection zone assumes a mixing length equal to the local
  pressure scale height. In the result the slope of the giant branch is
  satisfactorily reproduced. The effect of the mass on the evolutionary
  track is investigated with stars of 1.0 and 1.2Mo. The effect of the
  chemical composition is also studied, metal content and helium content
  being varied independently. At constant Y (Y = 0), Z = 0, Z = 0.001,
  and Z = 0.01 evolutionary tracks are compared. At constant Z (Z =
  0.001), Y = 0, and Y = 0 25 cases are similarly compared. Agreement with
  observation, for various metal contents is reasonable. There is no way
  to check the effect of helium content at the present time. Finally,
  uncertainties in our knowledge of bolometric corrections and (B - V)
  colors for a given effective temperature are pointed out.

Title: Evolution of Population II Stars.
Authors: Demarque, Pierre
Bibcode: 1962AJ.....67Q.270D
Altcode:
  The evolution of Population II stars into the red-giant region
  in the H-R diagram is investigated following a method recently
  used by Kippenhahn, Temesrary, and Biermann (Z. Astrophys. 46,
  257, 1958) who emphasized the importance of the structure of the
  hydrogen convection zone to determine the radius of red giants,
  and consequently their position in the H-R diagram. (1) The central
  region forms an isothermal partially degenerate core of helium
  (Hoyle and Schwarzschild, Astrophys. J. Suppl. 2, 1, 1955). Both the
  pressure of the degenerate electron gas and the non- degenerate nuclei
  are taken into account. The mass of the core increases as the star
  evolves. (2) The energy generation is due to both proton- proton chain
  and carbon-nitrogen cycle. It is concentrated in a shell surrounding
  the helium core of the star. (3) The opacity is that given by Keller
  and Meyer- ott (Astrophys. J. 122, 32, 1955). (4) The outer boundary
  conditions are obtained from a model atmosphere. The structure of the
  hydrogen convection zone is calculated assuming the mixing length to
  be of the order of the local pressure scale height. The main purpose
  of this work is to investigate the differential effects of various
  chemical compositions on the evolutionary track. Calculations have
  been performed for stars of 1.2 and 1.0 solar masses. The results are
  compared to previous models and cluster color-magnitude diagrams.

Title: Models for Lower Main-Sequence Population II Stars.
Authors: Demarque, Pierre
Bibcode: 1961ApJ...134....9D
Altcode:
  Metal-deficient lower main-sequence stellar models by the author (Ap
  J, 132,366) are reconstructed by making a new assumption regarding the
  structure of the hydrogen convection zone. The mixing length 1 is taken
  to be 1 = 2H, instead of 1 = H as previously assumed The position of
  the resulting models in the N-R diagram is little changed, although,
  as expected, a shallow region of the hydrogen convection zone is
  considerably affected.

Title: Interior models for subdwarf stars
Authors: Demarque, Pierre
Bibcode: 1960AJ.....65..396D
Altcode:
  No abstract at ADS

Title: The Structure of Population II Stars.
Authors: Demarque, Pierre
Bibcode: 1960ApJ...132..366D
Altcode:
  Interior models for metal-deficient stars are constructed for values
  of Z = 0.001, Z = 0.005, and Z = 0.01, for masses ranging from 0.6 to
  1.0 solar mass, and hydrogen content X varying from 0.75 to 0.99 by
  weight. The models have a structure similar to that of red dwarf stars,
  investigated by Osterbrock in 1953. They have a radiative core and a
  convective envelope in adiabatic equilibrium. The energy production is
  due to the proton-proton reaction, and Keller and Meyerott's tables
  (1955) are used for the opacity. In order to know the depth of the
  convective zone and therefore the position of the star in the Hertz-
  sprung-Russell dia,gram, the outer boundary conditions as given
  by the physical conditions in the subphotospheric layers must i?e
  determined. In the atmosphere of stars with effective temperatures in
  the vicinity of the sun's, the temperature gradient does not approach
  the adiabatic `gradient as soon as convection sets in; there is an
  intermediate zone where one bas to take into account the effect of the
  super- adiabatic gradient. Model atmospheres are constructed, making
  use of the theory of the mixing length as developed by Biermann. Both
  cores and atmospheres were integra'ted with the help of the University
  of Toronto IBM 650 computer. Integrations for adiabatic envelopes'
  have been given by Ost'erbrock (1953). The resulting models' enable
  `is to establish clearly the respective positions of main sequences for
  stars of various compositions in the theoretical Hertzsprung-Russeli
  diagram. It is found that the shifts in position between main
  sequences of different chemical contents do not exceed a few tenths
  of a magnitude, even in cases of extreme metal deficiency. This is in
  good agreement with recent observational results. The massluminosity
  law, nevertheless, is not unique for stars with different chemical
  abundances.

Title: The Structure of Subdwarf Stars.
Authors: Demarque, Pierre Raymond
Bibcode: 1960PhDT.........2D
Altcode:
  No abstract at ADS

Title: The structure of subdwarf stars.
Authors: Demarque, Pierre
Bibcode: 1959AJ.....64..327D
Altcode:
  It is generally accepted that the subdwarfs are characterized by a low
  metal abundance. The present investigation indicates that the helium
  content also plays a role in differentiating among subdwarfs. Interior
  models for subdwarf stars were constructed assuming a low heavy-element
  content, i.e., Z = 0.001, for masses ranging from 0.6 to 1.0 solar mass,
  and hydrogen content varying from 0.75 to 0.999 by weight. The models
  have a structure similar to that of red dwarf stars, investigated by
  Osterbrock: they have a radiative core and a convective envelope in
  adiabatic equilibrium. The energy production was assumed to be due to
  the proton-proton reaction, and Keller and Meyerott's tables were used
  for the opacity. In order to determine the depth of the convective
  zone, and therefore the position of the star in the H-R diagram,
  the outer boundary conditions as given by the physical conditions in
  the subphotospheric layers must be determined. In the atmospheres
  of stars with effective temperatures in the vicinity of the sun's,
  the temperature gradient does not approach the adiabatic gradient as
  soon as convection sets in. There is therefore an intermediate zone
  where one has to take into account the effect of the superadiabatic
  gradient. Such model atmospheres were constructed, making use of the
  theory of the mixing length as developed by Biermann. Both cores and
  atmospheres were integrated with the help of the University of Toronto
  IBM 650 computer. The resulting models are situated in the sub- dwarf
  region of the theoretical H-R diagram. One notices that for a given
  mass the helium content strongly affects the radius and therefore the
  effective temperature, in the sense that abundant helium makes for a
  smaller star with higher surface temperature. Unfortunately, comparison
  with observation is difficult because the actual position of observed
  subdwarfs in the L log - log Te diagram is still uncertain. The L0
  results can be used to estimate the masses and helium content of
  stars in globular clusters. David Dunlap Observatory Richmond Hill,
  Ont., Canada

