Effects of Semiconvection on the Horizontal-Branch
Abstract
Summary. The effects of semiconvection on the horizontal-branch evolution of a 0.60 M0 Population II star with the envelope composition parameters X =0.732 and Z =0.001 are investigated. Following an initial phase of convective-core overshooting the models form a semiconvective zone which at its maximum extent results in the depletion of helium out to a mass value of 0.25 M0. A comparison between sequences computed with and without a treatment of semiconvection indicates that the neglect of semiconvection will (a) reduce the length of the horizontal-branch track by a factor of 1.8 and (b) decrease the horizontalbranch lifetime by a factor of 1.9. A number of additional horizontal-branch sequences including a treatment of semiconvection are presented over the mass range from 0.51-0.65 M0. These sequences suggest that a mass spread on the order of 0.05 M0 would be sufficient to produce a dispersion of 0.30 in log Teff over the log Teff interval from roughly 3.70-4.15. Key words: stellar evolution - semiconvection - honzontal-branch - Population II stars
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- September 1972
- Bibcode:
- 1972A&A....20..445S