Atmospheres for hot, high-gravity stars. II - Pure helium models

Abstract

An extensive grid of pure helium stellar model atmosphere calculations for hot, high-gravity stars is presented in order to elucidate the nature and characteristics of the progenitors of the DB white dwarfs. Surface gravities range from log g equals 6.0 (1.0) 9.0, and the effective temperatures from 25,000 K at log g equals 6.0 and 8.0 up to temperatures close to the Eddington limit at each gravity. All models assume (1) hydrostatic equilibrium, (2) steady-state statistical equilibrium, (3) pure helium composition, and (4) plane-parallel geometry. In addition, most are unblanketed and in LTE, and include convective heat transport. It is shown that neutral helium lines are stronger than the unblanketed values by about 15 percent, while the singly-ionized helium lines are found to be strengthened by about 25 percent over a large range of surface gravities and effective temperatures. Multichannel colors and detailed He 1 profiles are tabulated for all LTE unblanketed models.