Does the upper main sequence extend across the whole H-R diagram

Details Does the upper main sequence extend across the whole H-R diagram Does the upper main sequence extend across the whole H-R diagram

Jan 1977

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977apj...211..189s&link_type=abstract

Astrophysical Journal, vol. 211, Jan. 1, 1977, pt. 1, p. 189-197.

Astronomy and Astrophysics

Astrophysics

74

Hertzsprung-Russell Diagram, Main Sequence Stars, Opacity, Radiative Transfer, Stellar Evolution, Stellar Models, Hydrogen Atoms, Nuclear Reactions, Reaction Kinetics, Stellar Envelopes, Stellar Luminosity, Stellar Mass Ejection, Stellar Temperature, Supergiant Stars

Scientific paper

The effect of using Carson's (1976) radiative opacities in evolutionary sequences of stellar models has been studied over the mass range from 7 to 60 solar masses. The opacities are very large in the outer part of the envelope and induce such enormous radii for masses greater than about 30 solar masses for a heavy-element fraction of 0.02 or about 20 solar masses for a heavy-element fraction of 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 (in logarithms) of 3.6 to 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 exceeding 8 solar masses (heavy-element fraction of 0.02) or 6 solar masses (heavy-element fraction of 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.

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