Polarimetry of Be stars at 1.25 and 2.2 microns

Abstract

Presented are observations of the linear polarization of 8 Be stars at 1.25 and 2.2 microns. An equatorial disk model is developed where the polarization due to electron scattering of stellar and disk radiation is treated discretely, allowing two scatters of the stellar radiation and one of the disk radiation. Neutral hydrogen opacity is taken into account and the populations of the levels of hydrogen are allowed to depart from LTE if the dillute and diffuse fields indicate such a departure is necessary. ϕ Per, ζ Tau, γ Cas, and EW Lac all show a decrease in polarization longward of 1 micron. When combined with polarimetry in the visible model calculations indicate an increase in the density of the disk toward the star for these stars. 48 Lib, ε Cap, and o Aqr all maintain a high polarization into the near-infrared and each requires a different disk structure when modeled. The excess emission longward of 1 micron for these stars can be shown to arise in the disk.