Publication Abstracts

Stothers 1964

Stothers, R.B., 1964: Evolution of O Stars. II. Hydrogen exhaustion and gravitational contraction. Astrophys. J., 140, 510-523, doi:10.1086/147945.

The evolution of a star of 30 M is considered from the end of the stable phase of hydrogen burning to the onset of helium burning. Ten models are constructed for the hydrogen-exhaustion (E) phase, and six models for the gravitational contraction (G) phase.

The time scale of the E-phase is so short (8.8×104 years) that the shell source remains peaked at q = 0.34 and undergoes little hydrogen depletion. Because radiation pressure remains strong in the core, convection does not vanish when the hydrogen content at the center falls to zero. Gravitational contraction of the core contributes more to the luminosity than shell burning, but since the total luminosity changes little, the structure of the envelope is hardly affected. On the H-R diagram, the evolutionary track turns back toward the main sequence when Xc = 0.03, and does not turn away again until the shell source becomes important.

The G-phase begins when LH,core/L < 0.001, and lasts 9×108 years. Although the temperature in the shell increases, hydrogen depletion remains negligible because of the short time scale. However, the shell narrows considerably and its peak moves slightly inward for a while. The steep temperature gradient outside the shell causes the semiconvective zone to move inward to q = 0.48; the hydrogen discontinuity attains a value ΔX = 0.1. As the luminosity and radiation pressure in the shell simultaneously increase, the envelope expands. The shell then behaves like a node, since the core continues to contract. The convective region near the center shrinks asymptotically to a value q = 006, but at no time does the core approach an isothermal condition. The gravitational energy release is nearly uniform throughout the core in all phases. At the onset of helium burning, Tc = 1.5×1080 K and Pc = 270 gm/cm3. Because of the brightening shell source, the stellar radius increases rapidly, bringing the evolutionary track to completion of the typical S-shaped curve on the H-R diagram.

When helium starts to burn, the spectral type is B3, and the star is expected never to return to the region of O stars during its active life.

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BibTeX Citation

@article{st04910c,
  author={Stothers, R. B.},
  title={Evolution of O Stars. II. Hydrogen exhaustion and gravitational contraction},
  year={1964},
  journal={Astrophys. J.},
  volume={140},
  pages={510--523},
  doi={10.1086/147945},
}

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RIS Citation

TY  - JOUR
ID  - st04910c
AU  - Stothers, R. B.
PY  - 1964
TI  - Evolution of O Stars. II. Hydrogen exhaustion and gravitational contraction
JA  - Astrophys. J.
VL  - 140
SP  - 510
EP  - 523
DO  - 10.1086/147945
ER  -

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