Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983apj...264..228s&link_type=abstract
Astrophysical Journal, Part 1, vol. 264, Jan. 1, 1983, p. 228-236. Research supported by Lick Observatory, University of Califo
Astronomy and Astrophysics
Astrophysics
47
Abundance, Gaseous Diffusion, Globular Clusters, Helium, Hydrogen, Stellar Evolution, Hertzsprung-Russell Diagram, Red Giant Stars, Stellar Models
Scientific paper
Evolutionary calculations continuing until well past turnoff are presented for models of low-mass Population II stars which take into account the effects of the diffusion of helium relative to hydrogen. Evolutionary tracks, cluster isochrones and hydrogen distributions were obtained for stellar masses in the range 0.75 to 1.01 solar masses, both in the presence and absence of diffusion. It is found that for a star of a given mass, diffusion speeds up the evolutionary process on the main sequence, although after turnoff evolution is slowed with respect to the case without diffusion. As the stars ascend the red giant branch, their outer regions are remixed so that evidence of helium diffusion is erased, and the evolutionary tracks of the models with and without diffusion converge. Thus, if the age of a globular cluster is determined from the absolute magnitude at turnoff or from fitting isochrones, diffusion results in a 25% reduction in the derived age at a turnoff magnitude of 4.23, and a 14% reduction at a turnoff magnitude of 3.45.
Arigo R. J.
Bodenheimer Peter
Noerdlinger Peter D.
Stringfellow Guy S.
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