New Yonsei-Yale (Y2) Isochrones and horizontal-branch evolutionary tracks with helium enhancements

S. I. Han, Y. C. Kim, Y. W. Lee, S. K. Yi, D. G. Kim, P. Demarque

Research output: Chapter in Book/Report/Conference proceedingConference contribution

6 Citations (Scopus)


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 Y2 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.

Original languageEnglish
Title of host publicationGlobular Clusters - Guides to Galaxies
Subtitle of host publicationProceedings of the Joint ESO-FONDAP Workshop on Globular Clusters
EditorsTom Richtler, Soren Larsen
Number of pages2
Publication statusPublished - 2009

Publication series

NameESO Astrophysics Symposia
ISSN (Print)1431-2433
ISSN (Electronic)1611-6143

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Physics and Astronomy (miscellaneous)


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