Differential polarization of Hβ in γ CAS

High resolution ( 0.15 Å/pixel ) spectropolarimetry across the Hβ emission line of the Be star γ Cas is presented. The differential polarization and polarization angle vary both in profile and depth. It was found that the polarization profile fits the relation PL, = (Iunderlying / Itotal)Pc, instead of the generally accepted PL = PC / Iemmission (Coyne 1975). Assuming the absolute polarization in the adjoining continuum is constant, the polarization profile is used to determine Teff, geff, and v sin i for the underlying star by fitting the Hubeny (1988) atmosphere model. The Be star model developed by Poeckert and Marlborough (1978a) for γ Cas is used as a basis to explain our polarization observations. We have made two types of modifications to the model: the first being to revise the intrinsic properties of the underlying star; the other is to make more accurate treatment of the radiation transfer equation in the disk. A search of the parameter space was made to find the best fit. We find an adequate fit to the emission line profile, but only a poor fit to the polarization profile from Poeckert and Marlborough model.Science, Faculty ofPhysics and Astronomy, Department ofGraduat