Helium-Star Models with Optically Thick Winds: Implications for the Internal Structures and Mass-Loss Rates of Wolf-Rayet Stars

摘要

We construct helium (He) star models with optically thick winds and comparethem with the properties of Galactic Wolf-Rayet (WR) stars. Hydrostatic He-coresolutions are connected smoothly to trans-sonic wind solutions that satisfy theregularity conditions at the sonic point. Velocity structures in the supersonicparts are assumed by a simple beta-type law. By constructing acenter-to-surface structure, a mass-loss rate can be obtained as an eigenvalueof the equations. Sonic points appear at temperatures ~ 1.8e5 - 2.8e5 K belowthe Fe-group opacity peak, where the radiation force becomes comparable to thelocal gravity. Photospheres are located at radii 3-10 times larger than sonicpoints. The obtained mass-loss rates are comparable to those of WR stars. Ourmass-loss rate - luminosity relation agrees well with the relation recentlyobtained by Graefener et al. (2017). Photospheric temperatures of WR stars tendto be cooler than our predictions. We discuss the effects of stellar evolution,detailed radiation transfer, and wind clumping, which are ignored in thispaper.