Journal
ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES
Volume 136, Issue 2, Pages 417-437Publisher
IOP PUBLISHING LTD
DOI: 10.1086/321795
Keywords
cosmology : theory; globular clusters : general; stars : abundances; stars : evolution; stars : interiors
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We have constructed a new set of isochrones, called the Y(2) 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 alpha -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 alpha -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.
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