The polarization of Hβ in γ Cas

Extract

High resolution (0.15 Å/pixel) spectropolarimetry across the Hβ emission line of the Be star γ Cas is presented (solid line in Figure B), as well as the intensity profile (Figure A). Earlier observations of the linear polarization across the emission lines (P_L) in Be stars (Coyne 1975, Poeckert 1975) found that P_L is inversely proportional to the total intensity of the emission line. However, our data clearly show that the width of the polarization profile is much wider than that of the emission line. The dotted line in Figure B gives P_L, based on the relationship of: which follows directly from Coyne (1975), where I_A is the intensity of the underlying Hβ absorption feature, I_total the observed intensity profile, and P_C the polarization in the adjacent continuum. The underlying stellar profile of Hβ (dotted line in Figure C), adopted from models by Hubeny (1988), gives a good match to the wings of the depolarization profile.