Derived Parameters for NGC 6791 From High-Metallicity Isochrones
Abstract
We have computed 8, 10, and 12 Gyr isochrones and physically consistent models of zero-age red horizontal branch stars for stellar masses between 0.55 and 1.3~\msun, all at [Fe/H] $=+0.15$. Comparison to the NGC 6791 BVI photometry of Kałużny & Udalski (1992) and Montgomery, Janes & Phelps (1994) yields an age of $10.0\pm0.5$ Gyr at an apparent distance modulus $ 13.49 < \dmv < 13.70$. The color offsets required to fit the isochrones, combined with the spectroscopic results of Friel & Janes, imply that the foreground reddening to NGC 6791 lies in the range $0.24 > \ebv >0.19$ with $+0.27 <$ [Fe/H] $<+0.44$. The zero-age horizontal branch models suggest that the red horizontal branch stars of NGC 6791 have masses $\lesssim 0.7\msun$. The masses are similar to those found for M67 red clump stars by Tripicco, Dorman & Bell (1993) and for globular cluster red horizontal branch stars, despite higher and lower masses (respectively) in those cases. This suggests the presence of a mechanism that tends to reduce stellar envelopes on the zero-age horizontal branch {\it to} a given mass rather than {\it by} a given amount.
- Publication:
-
The Astronomical Journal
- Pub Date:
- April 1995
- DOI:
- 10.1086/117397
- arXiv:
- arXiv:astro-ph/9502020
- Bibcode:
- 1995AJ....109.1697T
- Keywords:
-
- Galactic Evolution;
- Horizontal Branch Stars;
- Metallic Stars;
- Stellar Mass;
- Astronomical Models;
- Astronomical Photometry;
- Metallicity;
- Stellar Color;
- Stellar Envelopes;
- Astrophysics;
- OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC 6791;
- Astrophysics
- E-Print:
- 23 pages, postscript file