The hydrogen profile, previous mixing, and loops in the H-R diagram during core helium burning

Details The hydrogen profile, previous mixing, and loops in the H-R diagram during core helium burning The hydrogen profile, previous mixing, and loops in the H-R diagram during core helium burning

Mar 1977

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977apj...212..507s&link_type=abstract

Astrophysical Journal, Part 1, vol. 212, Mar. 1, 1977, p. 507-512.

Astronomy and Astrophysics

Astrophysics

16

Cepheid Variables, Helium, Hydrogen, Nuclear Fusion, Stellar Evolution, Stellar Models, Abundance, Chemical Composition, Profiles, Stellar Envelopes, Stellar Mass

Scientific paper

Static models of 5-solar-mass stars burning core helium have been calculated which consist of three zones: the core of a 5-solar-mass evolutionary model whose outer boundary is the outer edge of the hydrogen-burning shell; an envelope with chemical composition constant from the surface inward; and an intermediate zone whose composition varies with mass fraction. Models differ in the composition profile of the intermediate zone. Both the total excess of helium in the intermediate zone over what would be present if it had the envelope composition and the distribution of this excess helium can significantly influence the effective temperature of the star. Large excesses and concentration to the shell favor redder stars. The effect of changing the composition profile inside the nuclear-burning shell is not clear. The rapid transition from red to blue in pre-Cepheid models in which deep convective mixing has occurred at the giant tip is the result of the helium distribution in the intermediate zone. A summary is given of factors that affect the composition profile at different stages of evolution and consequently affect the length of the Cepheid loop. The effect on models of changing input parameters may then be deduced from how the input change affects each of these factors.

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