4 research outputs found
Mass Loss In M67 Giants: Evidence From Isochrone Fitting
We present a study of the stellar content of the open cluster M67. We have
computed new evolutionary sequences of stellar models with solar abundance that
cover all phases of evolution from the Zero-Age Main Sequence to the bright end
of the Asymptotic Giant Branch (AGB). We examine the fit between the calculated
and the observed red giant branch (RGB) in particular, and discuss factors that
most influence its quality. The distinct color gap between the RGB and the
clump giants is compared with the temperature gap between the He-burning tracks
and the computed 5 Gyr isochrone. This purely differential approach strongly
indicates that the clump giants have M \lta 0.70\msun\ , implying an amount
of mass loss ( \msun) well in excess of that found in globular
cluster stars. Observational constraints on mass loss processes favor the
interpretation that mass loss in cool low-mass giant stars increases with
metallicity.Comment: 21pp., plain TeX astro-ph/yymmnn
Derived Parameters for NGC 6791 from High-Metallicity Isochrones
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] . Comparison to the NGC 6791 BVI
photometry of Ka{\l}u\.zny & Udalski (1992) and Montgomery, Janes & Phelps
(1994) yields an age of 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
[Fe/H] .
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.Comment: 23 pages, postscript fil