Rotating Stellar Atmospheres (Review Paper)

Abstract

AbstractThe effects of rapid rotation on the emergent energy distribution, line profiles, atmospheric motions and polarization are discussed. A simplified explanation of some of the effects is presented. Results of detailed radiation transfer calculations are briefly reviewed. The rotation can lead to circulation and turbulent motions in the photospheric layers which could affect the outflow from the Be stars. The rotation rates actually observed in the Be stars are sufficiently below the critical rate that many of the effects predicted by the plane parallel atmosphere calculations should be small. Nevertheless, the models are useful and necessary for estimating rotation speeds from lines that are widely separated in wavelength. The rapidly rotating photospheric models predict far too small an infrared excess, as well as too small an intrinsic polarization. The explanation of these observations requires that geometrically extended envelopes be considered. Theoretical models for the intrinsic polarization are critically discussed. It is stressed that polarization is a powerful diagnostic for determining the asymmetrical structure of the outer atmospheres of the Be stars.