On the Age Difference Between the Oldest Population I and the Extreme Population II Stars
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 andZ=0.02, andX=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.
- Publication:
-
Astrophysics and Space Science
- Pub Date:
- March 1977
- DOI:
- 10.1007/BF00651364
- Bibcode:
- 1977Ap&SS..47..151S
- Keywords:
-
- Galactic Evolution;
- Hertzsprung-Russell Diagram;
- Stellar Evolution;
- Stellar Models;
- Astronomical Models;
- Chemical Evolution;
- Globular Clusters;
- Star Clusters;
- Star Distribution;
- Astrophysics