CONTINUUM POLARIZATION BY ELECTRON-SCATTERING IN ROTATIONALLY DISTORTED, RADIATION-DRIVEN STELLAR WINDS - B[E] SUPERGIANTS

We have constructed a simple, axisymmetric, radiation-driven wind model for a rotating B[e] supergiant in order to determine the expected continuum linear polarization arising from electron scattering in the rotationally distorted wind driven by strong lines. We solve for the structure of the radiation driven wind along the rotation axis and in the equatorial plane with rotations at various fractions of the critical rotation speed. A simple combination of the polar and equatorial solutions is then used to obtain the structure of the wind in a meridional plane. We then compute the ionization-excitation equilibrium at a discrete grid of points in the meridional plane and use these results to evaluate the continuum linear polarization produced by single scattering of the photospheric radiation field. The rotationally distorted wind for a star rotating at 80% of the critical speed produces a polarization of approximately 1.5% on the red side of the Balmer limit, similar to the observational data for the B[e] star MWC 939. By choosing extreme values for some model parameters, it may also be possible to reproduce the polarization data for MWC 645. However, the model wind is completely ionized to 3000 stellar radii so that dust and molecules cannot exist closer to the star than this distance. Some directions for possible improvement of the model are briefly discussed.