Properties of the Scenario for the Formation of WR Stars as Post-Red Supergiants

Abstract

Grids of evolutionary models for single stars in the range 9–120 M _⊙ have been computed up to the end of the central C-burning phase with up-to-date stellar physics. In addition to other results these models allow us to study the main properties of the formation of WR stars as post-red supergiants (Maeder, 1981c). Three grids of models have been computed: one for constant mass evolution (grid A) and the other two (B and C) with mass loss. As there exists no unique parametrization representing, over the various spectral types, the mass loss rates $\dot M$ as a function of basic stellar parameters, we have used mass loss rates fitted on the observations, applying different laws for a) OB stars, b) B-G supergiants, c) red supergiants (RSG) and d) WR stars. At a given luminosity, the rates in grid C are twice as large ąs in grid B and both grids encompass the central bulk of the observed mass loss rates.