SELF-CONSISTENT MODELS OF WOLF-RAYET STARS AS HELIUM STARS WITH OPTICALLY THICK WINDS

We propose a helium star with a steady, optically thick wind as a first-order model for Wolf-Rayet stars. Using an enhanced opacity which is guided by results of recent opacity calculations, we obtain self-consistent solutions which are made up of an inner helium-burning core in hydrostatic equilibrium and an outer radiative envelope through which a steady state wind is accelerated. Our surface is at optical depth near unity. The models are of homogeneous composition (primarily helium) and are of mass in the range 9-30 M . . In the most massive model, the momentum of the mass flow exceeds the photon momentum at the photosphere by a factor of 30. Terminal wind velocities are of order 1000 km s-1; these velocities are lower limits, as we neglect line-driven wind acceleration above the photosphere. For an appropriate choice of the opacity enhancement law, models of different mass define a relationship between the mass-loss rate [log M (M . yr-1) from -5.5 to -3.5] and the photospheric temperature (T(ph) = 2-9 x 10(4) K) which is consistent with observed data. We also find a forbidden region in the low-temperature part of the H-R diagram where no thick wind solutions exist.