Ultraviolet and optical spectral variability in the Be star Gamma Cassiopeiae - A coronal model for the emission

This paper reports the presence of Mg II emission, the probable presence of Si IV emission, and the possible presence of N V absorption in the UV spectrum of the B0.5 IVe star Gamma Cas. Changes in these features on time scales of several months are described. The detached-ring and mass-exchange binary models are briefly discussed and shown to be inadequate for Gamma Cas. An ad hoc generalization of the detailed stellar-wind model of Poeckert and Marlborough (1978) is presented and suggested as being qualitatively compatible with the UV data as well as with photoelectric H-alpha observations and the X-ray outburst observed in 1976. The presence of a 1-solar-mass neutron star companion with an orbital period of about 4 yr is hypothesized.