On the age difference between the oldest Population I and the extreme Population II stars

Hideyuki Saio, Yukio Shibata, Mahiro Simoda

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

The age difference between the oldest Population I stars and the extreme Population II stars is investigated by comparison of observational H-R diagrams with theoretical results using the common input physics and computer program for both Populations. Chemical compositions adopted for Population I and II stars are, X=0.7 and Z=0.02, and X=2×10-4, respectively. Evidence collected indicates that the open cluster NGC 188 and the globular cluster M92 are the representative samples of the oldest Population I and extreme Population II stars, respectively. Comparison between the observed H-R diagrams and theoretical isochrones in terms of the luminosity of the subgiant region and the turnoff point for NGC 188 and M92, respectively, then suggests that there is a significant age difference between Population I and II objects. The uncertainty of the oxygen abundance in the extreme Population II stars and its effect on their age determination is briefly discussed.

Original languageEnglish
Pages (from-to)151-162
Number of pages12
JournalAstrophysics and Space Science
Volume47
Issue number1
DOIs
Publication statusPublished - 1977 Mar

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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