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All stellar evolution models for nucleosynthesis require an initial isotopic abundance set to use as a starting point. Generally, our knowledge of isotopic abundances of stars is fairly incomplete except for the Solar System. We present a…

Solar and Stellar Astrophysics · Physics 2015-06-04 Christopher West , Alexander Heger

We supplement recent evolutionary computations of canonical stellar models (i.e. with inefficient core overshooting) with Z=0.0002, 0.0004, 0.0006, 0.001, 0.004, 0.008 and suitable assumptions about the original He content. Evolutionary…

Astrophysics · Physics 2007-05-23 S. Degl'Innocenti , P. Cariulo , P. G. Prada Moroni , M. Marconi

Integrated light from distant galaxies is often compared to stellar population models via the equivalent widths of spectral features--spectral indices--whose strengths rely on the abundances of one or more elements. Such comparisons hinge…

Astrophysics · Physics 2009-06-23 A. Dotter , B. Chaboyer , J. W. Ferguson , H. -c. Lee , G. Worthey , E. Baron , D. Jevremovic

An improved algorithm for interpolating isochrones and isochrone population functions (IPFs), based on the scheme introduced by Bergbusch & VandenBerg (1992, APJS, 81, 163), is described. The computer programs (FORTRAN 77) and the grids of…

Astrophysics · Physics 2009-11-06 Peter A. Bergbusch , Don A. VandenBerg

Hubble Space Telescope (HST) fine guidance sensor observations were used to obtain parallaxes of eight metal-poor ([Fe/H] < -1.4) stars. The parallaxes of these stars determined by the revised Hipparcos reduction average 17% accuracy, in…

Standard evolutionary synthesis models rely on the assumption of a fully sampled stellar initial mass function (IMF). Under this assumption, the age, chemical composition, and IMF uniquely define the predicted absorption spectra. However,…

We present the effects due to alpha-element enhancement on surface brightness fluctuation magnitudes and broad-band colors in order to investigate the calibration zero-point. We study these effects at ages covering 0.1 to 13 Gyr and…

Astrophysics · Physics 2009-11-13 Hyun-chul Lee , Guy Worthey , John P. Blakeslee

Precise stellar ages from asteroseismology have become available and can help setting stronger constraints on the evolution of the Galactic disc components. Recently, asteroseismology has confirmed a clear age difference in the solar…

Astrophysics of Galaxies · Physics 2019-03-06 E. Spitoni , V. Silva Aguirre , F. Matteucci , F. Calura , V. Grisoni

A new method is presented to compute age estimates from theoretical isochrones using temperature, luminosity and metallicity data for individual stars. Based on Bayesian probability theory, this method avoids the systematic biases affecting…

Astrophysics · Physics 2009-11-10 Frederic Pont , Laurent Eyer

The evolution of the metal content of the universe can be tracked through rest-frame UV spectroscopy of damped Ly-$\alpha$ systems (DLAs). Gas-phase abundances in DLAs must be corrected for dust depletion effects, which can be accomplished…

We present an abundance analysis based on high resolution spectra of 10 stars selected to span the full range in metallicity in the Ursa Minor dwarf spheroidal galaxy. We find [Fe/H] for the sample stars ranges from -1.35 to -3.10 dex and…

Cosmology and Nongalactic Astrophysics · Physics 2015-05-19 Judith G. Cohen , Wenjin Huang

Stellar evolution models which include the effect of helium and heavy element diffusion have been calculated for initial iron abundances of [Fe/H] = -2.3, -2.1, -1.9 and -1.7. These models were calculated for a large variety of masses and…

Astrophysics · Physics 2011-02-11 Brian Chaboyer , W. H. Fenton , Jenica E. Nelan , D. J. Patnaude , Francesca E. Simon

ABRIDGED: METHODS: We have conducted a high-resolution spectroscopic study of 714 F and G dwarf and subgiant stars in the Solar neighbourhood. The star sample has been kinematically selected to trace the Galactic thin and thick disks to…

Astrophysics of Galaxies · Physics 2015-06-17 T. Bensby , S. Feltzing , M. S. Oey

We have performed the first extensive analysis of the impact of an [alpha/Fe]>0 metal distribution on broadband colors in the parameter space (surface gravity, effective temperature, metal content) covered by Galactic globular cluster…

Astrophysics · Physics 2009-11-10 Santi Cassisi , Maurizio Salaris , Fiorella Castelli , Adriano Pietrinferni

We have used an updated version of the empirically and semi-empirically calibrated BaSeL library of synthetic stellar spectra of Lejeune et al. (1997, 1998) and Westera et al. (1999) to calculate synthetic photometry in the UBVRIJHKLL'M,…

Astrophysics · Physics 2009-10-31 Thibault Lejeune , Daniel Schaerer

We present detailed chemical element abundance ratios of 17 elements in three metal poor stars in the Ursa Minor dwarf spheroidal galaxy, which we combine with extant data from the literature to assess the predictions of a novel suite of…

Astrophysics of Galaxies · Physics 2015-06-23 Ugur Ural , Gabriele Cescutti , Andreas Koch , Jan Kleyna , Sofia Feltzing , Mark I. Wilkinson

We present the current status of an effort to create an updated grid of low-mass stellar evolution mass tracks and isochrones computed using the Dartmouth stellar evolution code. Emphasis is placed on reliably extending the present grid to…

Solar and Stellar Astrophysics · Physics 2014-08-11 Gregory A. Feiden , Jaquille Jones , Brian Chaboyer

We present a new method to determine the star formation and metal enrichment histories of any resolved stellar system. This method is based on the fact that any observed star in a colour-magnitude diagram will have a certain probability of…

Astrophysics of Galaxies · Physics 2015-06-11 Emma E. Small , David Bersier , Maurizio Salaris

We aim to develop a model-driven deep learning approach to age determination, by training neural networks on stellar evolutionary grids. Contrary to the usual data-driven deep learning approach of using prior age estimates as training data,…

Astrophysics of Galaxies · Physics 2026-04-15 T. Boin , L. Casamiquela , M. Haywood , P. Di Matteo , Y. Lebreton , M. Uddin , D. R. Reese

We use nearby K dwarf stars to measure the helium-to-metal enrichment ratio, a diagnostic of the chemical history of the Solar Neighbourhood. Our sample of K dwarfs has homogeneously determined effective temperatures, bolometric…

Astrophysics · Physics 2009-11-13 Luca Casagrande , Chris Flynn , Laura Portinari , Leo Girardi , Raul Jimenez