Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...18510312t&link_type=abstract
American Astronomical Society, 185th AAS Meeting, #103.12; Bulletin of the American Astronomical Society, Vol. 26, p.1488
Astronomy and Astrophysics
Astronomy
Scientific paper
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 M_sun, all at [Fe/H] =+0.15. Comparison to the NGC 6791 BVI photometry of Ka{\l}uzny & Udalski (1992, Acta Astron., 42, 29) and Montgomery, Janes & Phelps (1994, AJ, 108, 585) yields an age of 10+/-0.5 Gyr at an apparent distance modulus 13.49 < (m-M)_v < 13.70. The color offsets required to fit the isochrones, combined with the spectroscopic results of Friel & Janes (1993, A&A, 267,75), imply that the foreground reddening to NGC 6791 lies in the range 0.24 > E(B-V) >0.19 with +0.27 < [Fe/H] <+0.44. These results are derived using a technique by which we predict color shifts and apply these to the isochrones to simulate progressively higher metallicities. The zero-age horizontal branch models suggest that the red horizontal branch stars of NGC 6791 have masses ≲ 0.7M_sun. This is similar to the results found for the M67 red horizontal branch stars by Tripicco, Dorman & Bell (1993, AJ, 106, 618), and for globular cluster branch stars, even though the M67 progenitors are ~ 0.2 M_sun more massive, and the globular cluster progenitors similarly less massive. This suggests the presence of a mechanism, not strongly dependent on metallicity, which reduces stellar envelopes on the zero-age horizontal branch to a given mass rather than by a given amount.
Bell Roger A.
Dorman Ben
Hufnagel Beth
Tripicco Michael J.
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