STATIONARY HYDRODYNAMIC MODELS OF WOLF-RAYET STARS WITH OPTICALLY THICK WINDS

We investigate the influence of a grey, optically thick wind on the su rface and internal structure of Wolf-Rayet (WR) stars. We calculate hy drodynamic models of chemically homogeneous helium stars with stationa ry outflows, solving the full set of stellar structure equations from the stellar center up to well beyond the sonic point of the wind, incl uding the line force originating from absorption lines in a parameteri zed way. For specific assumptions about mass loss rate and wind opacit y above our outer boundary, we find that the iron opacity peak may lea d to local super-Eddington luminosities at the sonic point. By varying the stellar wind parameters over the whole physically plausible range , we show that the radius of the sonic point of the wind flow is alway s very close to the hydrostatic stellar radius obtained in WR star mod els which ignore the wind. However, our models confirm the possibility of large values for observable WR radii and correspondingly small eff ective temperatures found in earlier models. We show further that the energy which is contained in a typical WR wind can not be neglected. T he stellar luminosity may be reduced by several 10%, which has a prono unced effect on the mass-luminosity relation. I. e., the WR masses der ived for a given luminosity may be considerably larger Thereby, also t he momentum problem of WR winds is considerably reduced, as well as th e scatter in the M vs. M diagram for observed hydrogen-free WN stars.