Intrinsic Polarization of Early-Type Stars with Extended Atmospheres

Polarimetric observations were made for forty Be and shell stars. About half of these stars show evidence of intrinsic polarization, in most cases changing with time. The wavelength dependence of intrinsic polarization has maxima at wavelengths longer than the limits of the Balmer and Paschen series of hydrogen. The ratio of the amount of intrinsic polarization in the ultraviolet spectral region of the UBV system to that in the blue is about 0.5, while for interstellar polarization it is akvays larger than 0.7. Changes of polarization with time were found for three B-type supergiants, for the eclipsing binaries TT Hya and V453 Sco, and for the -Rayet stars 0 Mus and HD 50896; for the latter star, polarization is larger in the ultraviolet than in the blue. There is no evidence of intrinsic polarization in the early- type stars which are not surrounded by extended envelopes or shells. Polarimetric observations were made for the stars for which diameters were measured with an intensity interferometer. An attempt has been made to separate intrinsic and interstellar polarization under the assumption that the color-dependence law of intrinsic as well as interstellar polarization is already sufficiently known.