Rotationally Extended Stellar Envelopes: Cas

Abstract

New high time- and spectral-resolution observations of γ Cas have revealed an intermittent periodicity (0·7 days) in emission line profile variations. Profiles of a number of weak spectral lines have been obtained including two He I double emission lines and some O-type absorption lines. Absorption- and emission-line profiles have been calculated for rotating stars by two independent methods. The observed profiles in the spectrum of γ Cas are fitted best by those computed for an O8 star rotating at break-up velocity and viewed at $$i\,=\,55^{\circ} \,\pm\,10^{\circ}$$ . A detailed model of the star and extended envelope is derived and explanations of the line profile and other spectral variations are proposed. The method is applicable to all rotating B stars.