Studies in Stellar Evolution. I. The Influence of Initial CNO Abundances in a Star of Mass 2.3.
Abstract
A series of evolutionary sequences have been calculated for a configuration of mass 2 3 M0. They cover late pre-main-sequence and main-sequence evolution and differ in their initial chemical compositions. Sequence I begins with concentrations of C, N, and 0 similar to observed atmospheric values published for stars predominantly of Population I. The C/N and 0/N ratios are considerably in excess of their equilibrium values, and there is found to be a pre-main-sequence adjustment period of carbon burning causing an additional pre-main-sequence dip in luminosity on the Hertzsprung-Russell diagram. Sequence IV shows that the dip becomes less marked if the total heavy-element concentration is reduced. Sequence II begins with nearly equilibrium abundances of C'2 and N'4 and the carbon dip is not seen. Sequence III illustrates the effect of increasing the 0/N ratio and confirms that 016 is only very gradually converted to CN isotopes. In a series of appendices we describe the physical approaches and approximations used in these calculations. They are intended to supplement the basic discussion of the numerical technique. They treat the equation of state, opacity, chemical composition changes due to hydrogen burning, chemical homogenization of convective regions, and the obtaining of a starting configuration for an evolutionary sequence.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 1965
- DOI:
- 10.1086/148194
- Bibcode:
- 1965ApJ...141.1019B