Structure and Evolution of Model Helium Stars

Author: Divine, Theodore Neil

Year: 1965

Degree: Dissertation (Ph.D.)

Advisor: Oke, J. Beverley

Committee Member: Unknown, Unknown

Option: Astronomy; Physics

DOI: 10.7907/G079-F390

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.

Numerical models have been constructed which describe the evolution of stars which are initially pure helium. The iterative technique, programed for a large computer, permits the inclusion of radiation pressure, electron degeneracy, electron scattering opacity, gravitational contraction, and detailed composition changing brought about by triple-alpha and ([alpha],[gamma]) reactions.

The twenty homogeneous (pure helium) models, which range in mass from 0.4 to 60M[...] form a "main sequence" on the left of the H-R diagram. Evolutionary sequences of models at 0.5, 1, and 6M[...] exhaust their central helium supply in times of 80, 12, and 0.8 million years. Thereafter the connective core models, which have remained near their main sequence positions, are replaced by shell source models of increasing luminosity. At all three masses the final composition of the helium-exhausted core is almost exclusively oxygen, although a reduced rate for Csuperscript 120[superscript 16] can lead to moderate fractions of carbon.

There is no clear indication that the models correspond to any group of observed stars. Massive helium star models may resemble Wolf-Rayet stars in mass, luminosity, and effective temperature.

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