Combined stellar structure and atmosphere models for massive stars. I. Interior evolution and wind properties on the main sequence.
We present the first "combined stellar structure and atmosphere models" (CoStar) for massive stars, which consistently treat the entire mass loosing star from the center out to the asymptotic wind velocity. The models use up-to-date input physics and state-of-the-art techniques to model both the stellar interior and the spherically expanding non-LTE atmosphere including line blanketing. Our models thus yield consistent predictions regarding not only the basic stellar parameters, including abundances, but also theoretical spectra along evolutionary tracks. On the same ground they allow us to study the influence of stellar winds on evolutionary models. In this first paper, we present our method and investigate the wind properties and the interior evolution on the main sequence (MS) at solar metallicity. The wind momentum and energy deposition associated with the MS evolution is given and the adopted wind properties are discussed. From our atmosphere calculations, which include the effect of multiple scattering and line overlap, we also derive theoretical estimates of mass loss driven by radiation pressure. These values are compared with the predictions from recent wind models of the Munich group (Pauldrach et al. 1990, 1994, Puls et al. 1995). While we find an overall agreement with most of their results, our estimates for the mass loss rates are larger for supergiants. Our rates are in better agreement with the observed values than those of Puls et al. (1995). A comparison between boundary conditions given by the conventional plane parallel and the new spherically expanding atmosphere approach is made. For the MS evolution the evolutionary tracks and the interior evolution are found to be basically unchanged by the new treatment of the outer layers. However, for stars close to the Eddington limit, a small uncertainty in the behaviour of the deep atmosphere is found which might marginally affect the evolution. Given the small spherical extension of the continuum forming layers in the considered evolutionary phases, the predicted stellar parameters differ negligibly from those obtained using plane parallel atmospheres.