Atmospheres for Hot, High-Gravity Pure Helium Stars. (original) (raw)

Abstract

An extensive grid is presented of pure helium stellar model atmosphere calculations for hot, high gravity stars. These models are intended to help elucidate the nature and characteristics of the progenitors of the DB white dwarfs. The surface gravity in our model grid ranges from log g = 6.0(1.0)9.0, whereas the effective temperature ranges from T = 25,000K at log g = 6.0 and 8.0 (T = 40,000K at log g = 7.0 and 9.0) up to temperatures close to the Eddington limit at each gravity. All our models assume hydrostatic equilibrium, steady state statistical equilibrium, pure helium composition, and plane-parallel geometry. Most of the models are unblanketed and in LTE, and include convective energy transport. In addition to these, smaller grids of NLTE models (assuming detailed radiative balance in the helium lines) and of LTE, helium-line blanketed models (including convective energy transport) were computed to assess the importance of these effects. For all LTE, unblanketed models, Greenstein's multichannel colors and detailed profiles are tabulated for the HeI 3889, 4026, 4387, 4438, 4471, 4713, 4921, 5015, 5047, 5876, 6678, 7065 and HeII 1085, 1640, 3203, 4340, 4542, and 4686 lines.