Pubs.GISS: Abstract of Stothers and Chin 1977

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Stothers and Chin 1977

Stothers, R., and C.-W. Chin, 1977: Does the upper main sequence extend across the whole H-R diagram. Astrophys. J., 211, 189-197.

The effect of using Carson's radiative opacities in evolutionary sequences of stellar models has been studied over the mass range from 7 to 60 M_☉. The opacities are very large in the outer part of the envelope and induce such enormous radii for masses greater than ~ 30 M_☉ (Z_e = 0.02) or ~ 20 M_☉ (Z_e = 0.04) that the evolutionary tracks during the phase of core hydrogen burning extend across the whole H-R diagram. The choice of the Schwarschild or Ledoux criterion for convection makes very little difference for the behavior of the tracks. Evolution through the effective-temperature range T_e = 3.6-4.0 occurs in all cases on a rapid (secular) time scale. Core helium burning takes place exclusively in the red-supergiant configuration for stellar masses > 8 M_☉ (Z_e = 0.02) or > 6 M_☉ (Z_e = 0.04). These stellar models seem to be in significantly better agreement with the observed distribution of bright stars on the H-R diagram than are the older models based on the Cox-Stewart opacities. It can be inferred that a large envelope opacity (e.g., Carson's) exists and that substantial mass loss takes place in very massive late-type supergiants.