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Stothers, R., 1963: Evolution of O stars. I. Hydrogen-burning. Astrophys. J., 138, 1074-1084.
The evolution of an O-type star of 30 M☉ is considered from its initial main-sequence state to the point where the hydrogen content of the core has decreased from 70 per cent to 7 per cent by weight. The O stars are characterized by convective instability in the envelope and the full CNO-cycle of energy generation. Radiation pressure is important throughout the star, and electron scattering dominates the opacity. The inhomogeneous models consist of four zones: (I) a radiative envelope retaining the initial composition, (II) an outer semiconvective zone with a continuously varying composition that has a discontinuity at the interface with (III) an inner radiative zone also with a continuously varying composition, and (IV) a homogeneous convective core. Due to increasing radiation pressure, the semiconvective zone grows more rapidly outward than inward, but produces little effect on the important stellar quantities. The mass fraction of the core decreases from 0.60 to 0.34 and the mean hydrogen content of the star gets 40 per cent depleted. The age, 4.7 million years, is shorter than that for other sequences computed for stars of mass ≈ 30 M☉ because of a higher luminosity. This is mainly the result of choosing a higher mean molecular weight and CNO content.
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