Far-ultraviolet emission lines in U Cephei : evidence for a hot, turbulent circumstellar envelope.

Abstract

U Cephei is a classical semidetached eclipsing binary of the Algol type, whose unusually high level of activity in the optical spectrum has long been recognized. This paper reports detection of numerous emission lines in the far-ultraviolet spectrum. For the first time, the line-emitting region has been studied both in emission and in absorption. It surrounds the hotter component and extends to a distance of several of its radii. A model is proposed in which the emission originates in a circumstellar region at an electron temperature of about 10,000K. This region is highly turbulent. The circumstellar material, coming from the Roche-filling secondary star, appears to have been at least partially processed by the CNO cycle.