Wolf-Rayet stellar evolution models with improved treatment of the atmosphere

Abstract

Evolutionary models of massive stars are quasi-exclusively computed using an Eddington gray atmosphere. This approximation does not accurately describe the complex physical phenomena occurring in the atmosphere of massive stars. We aim to include state-of-the-art atmosphere models in the evolution computations of massive stars and test how the Wolf-Rayet phase is impacted. We computed the evolution of Galactic massive stars with the code STAREVOL. During the advanced phases of evolution, we applied outer boundary conditions interpolated within a grid of CMFGEN model atmospheres at each time step. The effective temperature and effective gravity were extracted from the atmosphere models. We then compared the resulting evolutionary tracks with classical calculations assuming Eddington gray atmospheres. We find that including detailed model atmospheres has a significant impact on the effective radius and temperature of the models during the later stages of the evolution. The effective temperatures of the evolution models computed with detailed model atmospheres are greatly reduced and in better agreement with observations of Wolf-Rayet stars. On the other hand, the internal structure of the models is barely affected by the choice of the atmosphere. We show that applying post-processing corrections on effective temperature and gravity is a method equivalent to our direct inclusion of atmosphere models in evolutionary calculations. The inclusion of detailed atmosphere models in the computation of evolutionary models is necessary to correctly reproduce the position of evolved massive stars in the Hertzsprung-Russell diagram. However, this has no impact on the internal and chemical evolution.