A rotating, magnetic, radiation-driven wind model applied to Be stars

Abstract

The rotating magnetic hot star wind model of Friend and MacGregor (1984) is extended to include the treatment of an O or Be star as a finite disk. In O stars, the mass-loss rates become nearly independent of the surface magnetic field strength. In Be stars, rapid rotation sharply increases the mass-loss rate and, for magnetic fields on the order of 50 G or less, decreases the terminal velocity. If the poles of a Be star are identified with low rotation rate models and the equator with high rotation rate models, then the rotating wind model predicts that the equator will have a slower and denser wind then the poles. This model is consistent with observations that the mass-loss rate along the equator is orders of magnitude larger than the rate near the poles. However, the velocity law on the equator still reaches the terminal velocity within a few stellar radii, in contradiction to the slowly expanding disk suggested by the empirical models of H-alpha emission and infrared excess.