demarque

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

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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
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.

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Title: Stellar evolution models with entropy-calibrated mixing-length
parameter: application to red giants
Authors: Spada, Federico; Demarque, Pierre; Kupka, Friedrich
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.

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Title: Testing the entropy calibration of the radii of cool stars:
models of α Centauri A and B
Authors: Spada, Federico; Demarque, Pierre
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 αMLT, recently
developed and successfully applied to the Sun (Spada et al. 2018, ApJ,
869, 135). In this technique the value of αMLT 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 αMLT. 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 αMLT 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 αMLT 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.

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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.
2018ApJ...869..135S Altcode: 2018arXiv181101817S
Main-sequence, solar-like stars (M ≲ 1.5 M ⊙)
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 MLT, 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 MLT based on 3D
radiation hydrodynamics (RHD) simulations of convection. The value of α
MLT 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}eff}) 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.

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Title: YaPSI: a new database of evolutionary tracks and isochrones
Authors: Spada, F.; Demarque, P.; Kim, Y. -C.; Boyajian, T. S.;
Brewer, J. M.
2018IAUS..334..362S Altcode:
The Yale-Potsdam Stellar Isochrones (YaPSI) cover the low and
intermediate stellar mass regime (0.15 to 5.0 M⊙) 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.

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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
2018RNAAS...2..147B Altcode: 2018RNAAS...2c.147B
Not Available 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.

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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
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}⊙ and 1.018+/- 0.011 {M}⊙
 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}{Jup}. 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}⊙ , 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. 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.

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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.
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. 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. 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. (3 data files).

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Title: The Yale-Potsdam Stellar Isochrones
Authors: Spada, F.; Demarque, P.; Kim, Y. -C.; Boyajian, T. S.;
Brewer, J. M.
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}* &lt; 0.6 {M}⊙ ), 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}⊙
 densely enough to permit detailed interpolation in mass, and
the metallicity and helium abundance ranges [Fe/H] = -1.5 to +0.3
and Y 0 = 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}eff}-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.

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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
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. 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. 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.

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Title: Entropy in Adiabatic Regions of Convection Simulations
Authors: Tanner, Joel D.; Basu, Sarbani; Demarque, Pierre
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}{{eff}}, which holds potential for calibrating
stellar models in a simple and more general manner.

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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.
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⊙
and 0.592 ± 0.006 M⊙ 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⊙, 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. 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.

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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.
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.

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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
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
θLD = 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 (Teff = 4875 ± 43, 6092 ± 103 K),
stellar linear radii (R* = 0.805 ± 0.016, 1.203 ± 0.061
R⊙), mean stellar densities (ρ* = 1.62 ± 0.11,
0.58 ± 0.14 ρ⊙), planetary radii (Rp = 1.216
± 0.024, 1.451 ± 0.074 RJup), and mean planetary densities
(ρp = 0.605 ± 0.029, 0.196 ± 0.033 ρJup) 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 αMLT =1.34
need to be employed.

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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
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.

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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
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.

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Title: Modeling Convective Core Overshoot and Diffusion in Procyon
Constrained by Asteroseismic Data
Authors: Guenther, D. B.; Demarque, P.; Gruberbauer, M.
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 ⊙.

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Title: The Effect of Metallicity-dependent T-τ Relations on
Calibrated Stellar Models
Authors: Tanner, Joel D.; Basu, Sarbani; Demarque, Pierre
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.

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Title: The Chemical Composition Dependence of Stellar Envelope
Convection and Overshoot
Authors: Tanner, J. D.; Basu, S.; Demarque, P.
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
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.
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 ⊙) 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
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 eff &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
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.
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 Teff 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⊙) 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.
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, νmax,
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
νmax to estimate the preliminary asteroseismic mass,
which is confirmed with the modeling result (M = 1.45 ± 0.05 M
⊙) 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
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 Msolar 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
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. 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
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 Teff 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.
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. Data from Kepler.

---------------------------------------------------------
Title: 2D solar modeling
Authors: Ventura, P.; Penza, V.; Li, L.; Sofia, S.; Basu, S.;
Demarque, P.
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.
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, νmax. 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.
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.
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. 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.
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. αHp) 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.
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 sun, 0.85 M sun, 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.
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 ν0 = 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.
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
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
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.
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 20x20arcmin2. 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. 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
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. (1 data file).

---------------------------------------------------------
Title: Dissipation Efficiency of Turbulent Convection
Authors: Penev, Kaloyan; Sasselov, D.; Barranco, J.; Demarque, P.;
Robinson, F.
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 2) 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.
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 2 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.
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. 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 Y2 Isochrones Getting an Extra Dimension
Authors: Yi, Sukyoung K.; Kim, Yong-Cheol; Demarque, Pierre; Lee,
Young-Wook; Han, Sang-Il; Kim, Do Gyun
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 Y2 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.
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.
2008MNRAS.386.1625C Altcode: 2008arXiv0802.3243C; 2008MNRAS.tmp..416C
We report on a new, wide-field (20 × 20 arcmin2),
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. Based on
this result, we revise the properties of NGC 2112 using stellar models
from the Padova and Yale-Yonsei groups. 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. 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. This investigation
outlines the importance of a detailed membership analysis in the study
of disc star clusters. This paper includes data gathered with
the 6.5 Magellan Telescopes, located at Las Campanas Observatory,
Chile. 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. ‡
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.
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. 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). 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. 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. 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.
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.
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.
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. 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.
2007IAUS..239..388S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Comparing convection in the Sun with Procyon A
Authors: Robinson, Frank; Demarque, Pierre
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
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
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.
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.
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. 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. 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.
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
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.
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.
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.
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 10-4)
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.
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.
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.
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. 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.
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. 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
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.
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. 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. 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.
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
αOV&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 +/-0.05HP. 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 ΔαOV~=+0.10 between 1.5 and 15
Msolar. This theory places an upper limit on Procyon A's
core overshoot extent of ~0.4HP, 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.
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. 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
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 Y2
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: Y2 Isochrones with an Improved Core Overshoot
Treatment
Authors: Demarque, Pierre; Woo, Jong-Hak; Kim, Yong-Cheol; Yi,
Sukyoung K.
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 Y2 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.
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.
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.
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.
2004ESASP.559..313B Altcode: 2004soho...14..313B
No abstract at ADS

---------------------------------------------------------
Title: The Y 2 Isochrones
Authors: Yi, Sukyoung K.; Demarque, Pierre; Kim, Yong-Cheol
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.
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. 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
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 Γ1 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 104, we expect errors σY in the estimated
helium abundance to range from 0.03 for 0.8-Msolar stars to
0.01 for 1.2-Msolar 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 10-4.

---------------------------------------------------------
Title: A Preliminary Seismic Analysis of 51 Pegasi: Large and Small
Spacings from Standard Models
Authors: Murphy, Eric J.; Demarque, Pierre; Guenther, D. B.
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 Msolar, 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 1.10Msolar). 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.
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.
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 Γ1 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
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.
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.
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. 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.
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 Hp 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 10Hp scaling
law, based on 2D numerical simulations, suggests a few hundred cells
on a supergiant. 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. The convection scale size from
the giant simulation is compared to previous extrapolations and to
observation. 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.
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.
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 Y2 Stellar Evolutionary Tracks
Authors: Yi, Sukyoung K.; Kim, Yong-Cheol; Demarque, Pierre
2003ApJS..144..259Y Altcode: 2002astro.ph.10201Y
We present a database of the latest stellar models of the Y2
(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 Y2
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
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. 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
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. Based on observations collected at the European Southern Observatory,
Paranal, Chile (ESO 64.L-0385).

---------------------------------------------------------
Title: The Y2 Isochrones
Authors: Yi, S.; Demarque, P.; Kim, Y. C.
2003ASPC..296..240Y Altcode: 2003nhgc.conf..240Y
No abstract at ADS

---------------------------------------------------------
Title: The Y 2 Isochrones and Stellar Evolution Tracks
Authors: Yi, Sukyoung K.; Demarque, Pierre; Kim, Yong-Cheol
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.
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.
2003aahd.conf..509D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Stellar Convection
Authors: Demarque, Pierre; Robinson, Francis J.
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.
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.
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 Y2 Isochrones for α-Element Enhanced Mixtures
Authors: Kim, Yong-Cheol; Demarque, Pierre; Yi, Sukyoung K.; Alexander,
David R.
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 Y2 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.
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⊕ of iron (or ~40 M⊕ 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
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
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.
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.
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
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 Y2 Isochrones
Authors: Yi, S. K.; Demarque, P.; Kim, Y. -C.; Lee, Y. -W.; Ree,
C. H.; Lejeune, T.
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
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.
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
V0-MV in the range 6.35 to 6.38, which is in
excellent agreement with the distance modulus (m-M)0=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. (4 data files).

---------------------------------------------------------
Title: Towards Better Age Estimates for Stellar Populations: The
Y2 Isochrones
Authors: Demarque, Pierre; Yi, Sukyoung; Kim, Yong-Cheol
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.
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
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
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
Y2 Isochrones for Solar Mixture
Authors: Yi, Sukyoung; Demarque, Pierre; Kim, Yong-Cheol; Lee,
Young-Wook; Ree, Chang H.; Lejeune, Thibault; Barnes, Sydney
2001ApJS..136..417Y Altcode: 2001astro.ph..4292Y
We have constructed a new set of isochrones, called the Y2
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
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 Msolar for Z=Zsolar),
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
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 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 +22.9 km
s-1. 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
V0-MV in the range 6.35 to 6.38, which is in
excellent agreement with the distance modulus (m-M)0=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.
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.
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 logTeff 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.
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.
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.
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
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
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.
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 YZAMS=~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 YZAMS 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
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 Mv(RR) on metallicity in globular
clusters and the slope of the mean &lt;MV(RR)&gt;-[Fe/H]
relation. The SHB models confirm Lee's earlier finding that the
slope of the &lt;MV(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 MV(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 Mv(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 Mv(RR). Taking HB morphology into account,
we find that the slope of the mean &lt;MV(RR)&gt;-[Fe/H]
relation varies between 0.36 for the clusters with Galactocentric
distances Rgc less than 6 kpc and 0.22 for clusters with
6 kpc&lt;Rgc&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.
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 Msolar 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 Msolar. 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
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.
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.
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.
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
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)v=9.69+/-0.11 for M67 and (m-M)v=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/Msolar&gt;1.1) being more centrally concentrated than
those that are the least massive (0.8&gt;=M/Msolar&gt;0.65).

---------------------------------------------------------
Title: The Pulsation Properties of Procyon A
Authors: Chaboyer, Brian; Demarque, P.; Guenther, D. B.
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
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.
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
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.
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 H0 and Ω0, the
younger, metal-rich models would have no conflict with a cosmology
of a negligibly small Λ0, whereas the older, metal-poor
models unavoidably suggest a substantially large value of Λ0
(i.e., Λ0&gt;~0.63 for zfor=∞) 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
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.
1999ASPC..173..373D Altcode: 1999sstt.conf..373D
No abstract at ADS

---------------------------------------------------------
Title: Globular Cluster Ages: Overview
Authors: Demarque, P.
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.
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.
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.
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 × 10-12 yr-1 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.
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 Mv (RR Lyrae stars) = 0.39 +/- 0.08 (statistical) at
[Fe/H] = -1.9 with an additional uniform systematic uncertainty of
+0.13-0.18. 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. 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 H0
&lt;= 67 km s-1 Mpc-1). 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.
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.
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.
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 Teff 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.
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.
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.
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.
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}) {Msun 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 Msun} to {0.46
Msun}. 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.
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.
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. 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.
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. 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.
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)⊙. 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⊙
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⊙. The
seismic data are also incompatible with extensive rapid mixing of
4He in the solar envelope. This, we believe, also argues
against the possibility of slow mixing of 3He occurring
in a shell, as was recently proposed by Cumming and Haxton to lower
the 7Be/8B neutrino flux ratio. But we note
that the occurrence of some mixing of 3He and other trace
elements and isotopes in the region of the solar interior where the
initial 4He 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
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. 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 Teff because a
more metal-rich helium-burning star has a smaller mass than a metal-poor
one and because lifetime increases as mass decreases. 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
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 0.25Hp, where Hp
is the pressure scale height at the core edge. All four sets of
theoretical isochrones were adjusted to an adopted distance modulus of
Vdeg-MV=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 0.20Hp 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 0.25Hp 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
Vdeg-MV=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.
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
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.
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.
1996MNRAS.283..683C Altcode:
Globular cluster age estimates based on the absolute magnitude of the
main-sequence turn-off [Mv(TO)] are generally considered
to be the most reliable from a theoretical viewpoint. However, the
difficulty in determining Mv(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 [Mv(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 Mv(BTO) is similar to
Mv(TO). As a result, ages derived using Mv(BTO)
are at least a factor of 2 more precise than those derived using
Mv(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.
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.
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.
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.
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
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.
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
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
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
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. 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.
1996ASPC...92..269F Altcode: 1996fogh.conf..269F
We present the HST WFPC2 VIC 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
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.
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.
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.
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.
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
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.
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.
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.
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
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
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.
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.
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
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.
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-IC) 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
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.
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 Hp), 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 × 106 ergs cm-2
for the 8B 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.
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.
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 Hp)
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+1.0-0.5 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+0.5-0.3
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.
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-beta, 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.
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
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.
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.
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.
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.
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.
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.
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.
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.
1995somo.conf..151D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Helioseismology
Authors: Demarque, P.; Chaboyer, B.; Guenther, D. B.; Pinsonneault,
M. H.
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.
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
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-beta 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.
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.
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.
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 Hp) 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
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.
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, 10-10, 5 x 10-10, and 10-9
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 10-9 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
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 (RG) 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 RG 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.
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.
1994IAUS..162..131S Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: Diffusion and Rotational Mixing in Stellar Models
Authors: Chaboyer, Brian; Demarque, P.
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
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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
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.
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.
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.
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.
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.
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
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
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
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.
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.
1991IAUS..145...71D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Post-main-sequence solar evolution.
Authors: Demarque, Pierre; Guenther, David B.
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-Msun 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.
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
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
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.
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.
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.
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.
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.
1990BAAS...22.1206P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Evolution of Horizontal-Branch Stars: Theoretical Sequences
Authors: Lee, Young-Wook; Demarque, Pierre
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.
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
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.
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.
1990aadm.conf..275L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Seismology of Sun-like Stars
Authors: Demarque, P.; Guenther, D. B.
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.
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.
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.
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
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
1989PhRvL..62.1583D Altcode:
We present the results of new theoretical work on surface
7Li and 6Li 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;Ωbh2&lt;0.025 (where the Hubble
constant is 100h Km sec-1 Mpc -1), 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.
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.
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.
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.
1988plsm.book.....D Altcode:
The authors present the results of new theoretical work on surface
7Li and 6Li 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;
Ωbh2 &lt; 0.025, and impose limitations on
alternative nucleosynthesis scenarios.

---------------------------------------------------------
Title: Probing the Sun's Internal Rotation
Authors: Demarque, P.; Guenther, D. B.
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.
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.
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
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.
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.
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.
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.
1988asgc.conf...97D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Internal Constitution and Oscillation Spectrum of Procyon
Authors: Demarque, P.; Guenther, D. B.
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.
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.
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
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.
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
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
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.
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
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
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.
1986BAAS...18.1012Y Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Stellar Seismology of epsilon Eridani
Authors: Guenther, D. B.; Demarque, P.
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.
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.
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 - 4.5×109yr. 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.
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.
1985BAAS...17Q.904L Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: From solar dynamo to terrestrial climate
Authors: Sofia, S.; Demarque, P.; Endal, A.
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.
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.
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
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 2.5×10-10 &lt; M &lt; 1×10-9M_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.
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.
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.
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.
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.
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.
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.
1984BAAS...16..526C Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: Resonant three-wave interactions of solar g-modes
Authors: Guenther, D. B.; Demarque, P.
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.
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.
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.
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.
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.
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.
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.
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.
1982ApJ...259..193D Altcode:
We present evolutionary calculations of a 0.9 Msun 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 andgiants 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.
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
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.
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.
1982BAAS...14R.665C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Models for Horizontal-Branch Stars with Cores Enriched in
Carbon and Nitrogen
Authors: Demarque, P.
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.
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.
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.
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⊙ with Zero Heavy Element
Content
Authors: Demarque, P.; Guenther, D. B.
1980BAAS...12..833D Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: Ages and abundances of globular clusters and the oldest
open clusters.
Authors: Demarque, P.
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.
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
Teff]-plane and in the [MV- (B-V)]-diagram.
Authors: Ciardullo, R. B.; Demarque, P.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
1974Natur.252..368D Altcode:
ROOD and Ulrich1 have discussed the oblateness of solar
models with a rotating core. They find a larger oblateness for the same
model than we did2. We have looked again into the oblateness
calculation and now believe that the correct solution of the equations
of Goldreich and Schubert3 gives an oblateness for the final
model of our2 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.
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.
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.
1974ApJ...187..423D Altcode:
No abstract at ADS

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

---------------------------------------------------------
Title: Variable Stars and Evolution in Globular Clusters
Authors: Demarque, P.
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.
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.
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.
1973BAAS....5..406D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Effect of Overshoot Mixing in Old Galactic Clusters.
Authors: Prather, M. J.; Demarque, P.
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.
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.
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.
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.
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.
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.
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.
1973ASSL...36..187D Altcode: 1973vsgc.coll..187D; 1973IAUCo..21..187D
No abstract at ADS

---------------------------------------------------------
Title: Remarks on stellar abundances.
Authors: Demarque, P.
1973stag.conf...21D Altcode: 1973IAUCo..17...21D
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.
1972NPhS..239...85D Altcode: 1972Natur.239...85D
ON the basis of calculations of evolution of Population
II stars, Iben1 has shown that the ratio R of
theoretical horizontal branch (HB) to red giant (RG) lifetimes
(R = tHB/tRG) is a function of their helium
abundance. This ratio can also be written where NHB and
NRG 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
calibration2, Iben et al.3 then determined the
helium content of a number of globular clusters for which observations
were available4, 5. 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.
1972NPhS..239...55D Altcode: 1972Natur.239...55D
The theory of Feynman and Gell-Mann1 of weak interactions
predicts an electron-neutrino interaction (\emacr ve)
(\vmacr2 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. Ruderman2 and Chiu3 have discussed
various aspects of this problem. Stothers4 has reviewed
the relevant astrophysical data and concluded that so far all evidence
confirms the existence of the interaction. He further concluded that
g2=g2β × 10°+/-2,
where gβ is the β-decay coupling constant.

---------------------------------------------------------
Title: Effects of Semiconvection on the Horizontal-Branch
Authors: Sweigart, A. V.; Demarque, P.
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.
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.
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.
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.
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: Concluding Remarks
Authors: Demarque, P.
1972ade..coll...21D Altcode: 1972IAUCo..17...21D
No abstract at ADS

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

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

---------------------------------------------------------
Title: Is There a Black Hole in ɛ Aurigae?
Authors: Demarque, Pierre
1971Natur.230..516D Altcode:
THE suggestion has been made1,2 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 holes3 and the research by Wilson4 on the
dynamics of the supernova phenomenon, which indicates that collapsed
objects may be quite common in the galaxy, make Cameron's1
suggestion particularly intriguing.

---------------------------------------------------------
Title: Advanced Evolution of Population II Stars. I. Red Giants and
the Helium Flash
Authors: Demarque, Pierre; Mengel, John G.
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.
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.
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: The Early Evolution of Population II Stars. II
Authors: Demarque, Pierre; Mengel, John G.; Aizenman, Morris L.
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.
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.
1970BAAS....2Q.308D Altcode:
No abstract at ADS

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

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

---------------------------------------------------------
Title: Yale University Observatory, New Haven, Connecticut. Report
1968-1969.
Authors: Demarque, P.
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.
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.
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.
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.
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
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.
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
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
1967ApJ...150..723B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Hyades Distance Modulus and Stellar Interiors.
Authors: Demarque, Pierre
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
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.
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.
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.
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.
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.
1966stev.conf..231D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Upper Main Sequence
Authors: Morris, Stephen C.; Demarque, Pierre
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.

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Title: Models for Lower Main-Sequence Population II Stars.
Authors: Demarque, Pierre
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.

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

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Title: The Structure of Population II Stars.
Authors: Demarque, Pierre
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.

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

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Title: The structure of subdwarf stars.
Authors: Demarque, Pierre
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