Ionization structure in the disks and winds of B[e] stars

Abstract

We investigate the ionization structure in the non-spherical winds and disks of B[e] stars. Especially the luminous B[e] supergiants seem to have outflowing disks which are neutral in hydrogen already close to the stellar surface. The existence of neutral material so close to the central star is surprising and needs to be investigated in detail. We perform our model calculations mainly in the equatorial plane, trying to find a plausible scenario that leads to recombination in the vicinity of the hot stars. Two different approaches are presented that both result in a hydrogen neutral equatorial region. We especially focus on the influence of stellar rotation which is known to play a significant role in shaping non-spherical winds. We show that a rotating star can have a neutral equatorial wind, even without the need of a density enhancement due to bi-stability or wind compression, but simply due to graviational darkening in combination with the known high mass-loss rates of the B[e] stars and especially the B[e] supergiants.