Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.3604t&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #36.04; Bulletin of the American Astronomical Society, Vol. 24, p.1175
Astronomy and Astrophysics
Astronomy
Scientific paper
As part of an ongoing project to generate synthetic integrated spectra covering a range of chemical compositions and ages, we have calculated a new set of solar abundance evolutionary tracks. These have been used to produce isochrones for ages between 4 and 16 Gyr. Rather than using a color-temperature conversion table, as is generally done, we instead calculate detailed synthetic spectra at intervals along the isochrones and so directly determine colors for a variety of photometric filter systems. As a test we have compared the 5 Gyr isochrone from this set to the color-magnitude diagram of the well-studied old open cluster M67. The fit is quite good from the unevolved main sequence through the turnoff and continuing up the first ascent giant branch if an apparent distance modulus of (m-M)_V=9.50 and reddening of E(B-V)=0.032 are used. The isochrones assume a Helium abundance Y=0.27 and convective parameter alpha =1.6. The effect of variations in alpha and in the surface pressure boundary condition (based on model atmospheres) are discussed. Evolution through the He-burning phases has also been included in a consistent manner. Differential comparison of the zero-age horizontal branch and subsequent evolutionary tracks for various masses with the position of the M67 clump giants reveals a surprisingly large amount of mass loss; masses of less than 0.70 M_&sun; are strongly indicated. The implications of this loss of nearly half the stellar mass are examined. This work has been supported in part by NSF grant AST-9122361
Bell Roger A.
Dorman Ben
Tripicco Michael J.
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