Publications (43)
Two-Dimensional Stellar Evolution Code Including Arbitrary Magnetic Fields. II. Precision Improvement and Inclusion of Turbulence and Rotation
Linghuai Li, Sabatino Sofia, Paolo Ventura +4
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…
The Relative Ages of Galactic Globular Clusters
Ata Sarajedini, Brian Chaboyer, Pierre Demarque
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…
On Dissipation inside Turbulent Convection Zones from 3D Simulations of Solar Convection
Kaloyan Penev, Dimitar Sasselov, Frank Robinson +1
The development of 2D and 3D simulations of solar convection has lead to a picture of convection quite unlike the usually assumed Kolmogorov spectrum turbulent flow. We investigate…
The theoretical calculation of the Rossby number and the `non-local' convective overturn time for pre-main sequence and early post-main sequence stars
Yong -Cheol Kim, Pierre Demarque
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 p…
Entropy in adiabatic regions of convection simulations
Joel D. Tanner, Sarbani Basu, Pierre Demarque
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 mixi…
Hubble Space Telescope Astrometry of the Procyon System
Howard E. Bond, Ronald L. Gilliland, Gail H. Schaefer +9
The nearby star Procyon is a visual binary containing the F5 IV-V subgiant Procyon A, orbited in a 40.84 yr period by the faint DQZ white dwarf Procyon B. Using images obtained ove…
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
Tabetha Boyajian, Kaspar von Braun, Gregory A. Feiden +24
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 angul…
Modelling fully convective stars in eclipsing binaries: KOI-126 and CM Draconis
Federico Spada, Pierre Demarque
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 con…
On the UV Bright Phase of Metal-Rich Horizontal-Branch Stars
Sukyoung Yi, Pierre Demarque, Yong-Cheol Kim
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…
Space and Ground Based Pulsation Data of Eta Bootis Explained with Stellar Models Including Turbulence
Christian W. Straka, Pierre Demarque, D. B. Guenther +2
The space telescope MOST is now providing us with extremely accurate low frequency p-mode oscillation data for the star Eta Boo. We demonstrate in this paper that these data, when…
A Lower Limit on the Age of the Universe
Brian Chaboyer, Peter J. Kernan, Lawrence M. Krauss +1
We report the results of a detailed numerical study designed to estimate both the absolute age and the uncertainty in age (with confidence limits) of the oldest globular clusters.…
NGC 6791: an exotic open cluster or the nucleus of a tidally disrupted galaxy?
Giovanni Carraro, Sandro Villanova, Pierre Demarque +3
We report on high resolution Echelle spectroscopy of 20 giant stars in the Galactic old open clusters NGC 6791 obtained with Hydra at the WIYN telescope. High precision radial velo…
Helium-Abundance and Other Composition Effects on the Properties of Stellar Surface Convection in Solar-like Main-sequence Stars
Joel D. Tanner, Sarbani Basu, Pierre Demarque
We investigate the effect of helium abundance and -element enhancement on the properties of convection in envelopes of solar-like main-sequence stars stars using a grid of 3D r…
Seismic Test of Solar Models, Solar Neutrinos and Implications for Metal-Rich Accretion
R. A. Winnick, Pierre Demarque, Sarbani Basu +1
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…
Calculation of Solar P-mode Oscillation Frequency Splittings Based on a Two-dimensional Solar Model
Linghuai Li, Sarbani Basu, Sabatino Sofia +1
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.
Modelling of Shallow and Inefficient Convection in the Outer Layers of the Sun Using Realistic Physics
Yong -Cheol Kim, Peter A. Fox, Sabatino Sofia +1
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…
Observations of Binary Stars with the Differential Speckle Survey Instrument. V. Toward an Empirical Metal-Poor Mass-Luminosity Relation
Elliott P. Horch, William F. van Altena, Pierre Demarque +6
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 imagi…
Core Overshoot: An Improved Treatment and Constraints from Seismic Data
Christian W. Straka, Pierre Demarque, D. B. Guenther
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 to…
Modeling Kepler Observations of Solar-like Oscillations in the Red-giant Star HD 186355
Chen Jiang, Biwei Jiang, Jorgen Christensen-Dalsgaard +11
We have analysed 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, wh…
A Precision Age Determination Technique for Globular Clusters
Brian Chaboyer, Pierre Demarque, Peter Kernan +2
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.…
The YY Isochrones for alpha-element Enhanced Mixtures
Yong -Cheol Kim, Pierre Demarque, Sukyoung K. Yi +1
We present a new set of isochrones in which the effect of the alpha-element enhancement is fully incorporated. These isochrones are an extension of the already published set of YY…
Comparing the Effect of Radiative Transfer Schemes on Convection Simulations
Joel D. Tanner, Sarbani Basu, Pierre Demarque
We examine the effect of different radiative transfer schemes on the properties of 3D simulations of near-surface stellar convection in the superadiabatic layer, where energy trans…
Super Helium-Rich Population and the Origin of Extreme Horizontal-Branch Stars in Globular Clusters
Young-Wook Lee, Seok-Joo Joo, Sang-Il Han +7
Recent observations for the color-magnitude diagrams (CMDs) of the massive globular cluster Omega Centauri have shown that it has a striking double main sequence (MS), with a minor…
On the Origin of the UV Upturn in Elliptical Galaxies. II. Test of the HB Hypothesis
Sukyoung Yi, Pierre Demarque, Augustus Oemler
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 previou…
Asteroseismic determination of helium abundance in stellar envelopes
Sarbani Basu, Anwesh Mazumdar, H. M Antia +1
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 ob…
A Preliminary Seismic Analysis of 51 Peg: Large and Small Spacings from Standard Models
Eric J. Murphy, Pierre Demarque, D. B. Guenther
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 dia…
The Metallicity Dependence of RR Lyrae Absolute Magnitudes from Synthetic Horizontal-Branch Models
Pierre Demarque, Robert Zinn, Young-Wook Lee +1
A grid of synthetic horizontal-branch (SHB) models based on HB evolutionary tracks with improved physics has been constructed to reconsider the theoretical calibration of the depen…
Y2 Isochrones with an Improved Core Overshoot
Pierre Demarque, Jong-Hak Woo, Yong-Cheol Kim +1
Convective core overshoot affects stellar evolution rates and the dating of stellar populations. In this paper, we provide a patch to the isochrones with an improved treatmen…
Evidence for strong progenitor age dependence of type Ia supernova luminosity standardization process
Young-Wook Lee, Chul Chung, Pierre Demarque +3
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 wo…
Variation of Stellar Envelope Convection and Overshoot with Metallicity
Joel D. Tanner, Sarbani Basu, Pierre Demarque
We examine how metallicity affects convection and overshoot in the superadiabatic layer of main sequence stars. We present results from a grid of 3D radiation hydrodynamic simulati…
Stellar evolution models with entropy-calibrated mixing-length parameter: application to red giants
Federico Spada, Pierre Demarque, Friedrich Kupka
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…
Evolution of Stellar Collision Products in Globular Clusters -- I. Head-on Collisions
Alison Sills, James C. Lombardi, Charles D. Bailyn +3
We explore the evolution of collisionally merged stars in the blue straggler region of the HR diagram. The starting models for our stellar evolution calculations are the results of…
Detection of solar-like oscillations from Kepler photometry of the open cluster NGC 6819
Dennis Stello, Sarbani Basu, Hans Bruntt +49
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 theor…
On the Origin of the UV Upturn in Elliptical Galaxies. I. Sensitivity of UV Population Synthesis to Various Input Parameters
Sukyoung Yi, Pierre Demarque, Augustus Oemler
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 po…
The Effect of Metallicity-Dependent T-tau Relations on Calibrated Stellar Models
Joel D. Tanner, Sarbani Basu, Pierre Demarque
Mixing length theory is the predominant treatment of convection in stellar models today. Usually described by a single free parameter, alpha, the common practice is to calibrate it…
Asteroseismic Diagnostics of Stellar Convective Cores
Anwesh Mazumdar, Sarbani Basu, Braxton L. Collier +1
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…
The Y^2 Stellar Evolutionary Tracks
Sukyoung K. Yi, Yong -Cheol Kim, Pierre Demarque
We present a database of the latest stellar models of the (Yonsei-Yale) collaboration. This database contains the stellar evolutionary tracks from the pre-main-sequence birth…
Empirical Constraints on Convective Core Overshoot
Jong-Hak Woo, Pierre Demarque
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 unsat…
The Sirius System and its Astrophysical Puzzles: Hubble Space Telescope and Ground-Based Astrometry
Howard E. Bond, Gail H. Schaefer, Ronald L. Gilliland +11
Sirius, the seventh-nearest stellar system, is a visual binary containing the metallic-line A1 V star Sirius A, brightest star in the sky, orbited in a 50.13-year period by Sirius…
The Non-Homologous Nature of Solar Diameter Variations
Sabatino Sofia, Sarbani Basu, Pierre Demarque +2
We show in this paper 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 hot stars in orbit around the M31 central supermassive black hole: are they young or old?
Pierre Demarque, Shanil Virani
AIMS: The cluster of hot stars observed in orbit around the central black hole of M31 has been interpreted as a 200 Myr starburst. The formation of a population of young stars in c…
Dissipation Efficiency in Turbulent Convective Zones in Low Mass Stars
Kaloyan Penev, Dimitar Sasselov, Frank Robinson +1
We extend the analysis of Penev et al. (2007) to calculate effective viscosities for the surface convective zones of three main sequence stars of 0.775Msun, 0.85Msun and the presen…
The old open cluster NGC 2112: updated estimates of fundamental parameters based on a membership analysis
Giovanni Carraro, Sandro Villanova, Pierre Demarque +2
We report on a new, wide field (), multicolor (), photometric campaign in the area of the nearby old open cluster NGC 2112. At the same time,…