Polarization in Be Stars: (Review Paper)

Abstract

A review of polarization produced in the extended circumstellar disks about Be stars is given. While variability of the polarization and its peculiar wavelength dependence in wide-band continuum measurements are discussed, emphasis is placed upon the recently discovered polarization effects in the emission lines and upon a discussion of models. Scattering in the photosphere of a star, even one rigidly rotating near breakup velocity, does not explain the observations. Better fits to the observations are obtained by scattering from electrons in a flattened gaseous disk extending some 10 stellar radii from the star with electron temperatures Te ≅ 10 000 K and electron densities Ne ≅ 1012 cm−3. In some stars the emission flux in Hα and Hβ appears to be partly polarized.