The interacting early-type contact binary SV Cen.

Abstract

Extensive optical and UV observations of SV Cen (b1 V + B6.5III) were obtained between 1978 and 1981. Orbital elements and absolute dimensions were derived from the data. The period-time diagram between 1894 and 1981 shows a large rate of period decrease of -2.15 x 10 to the -5th/yr in average, which exhibits pronounced variations with time. The unsteady period changes can be explained by mass loss through an outer Lagrangian point, in terms of loss of angular momentum carried away by the ejected matter. The UV spectroscopy revealed an expanding circumbinary envelope. A UV resonance line profile analysis indicates the occurrence of sudden ejections of matter forming radially expanding condensed shells in the envelope; these short-term fluctuations of the stellar wind are of a time scale of only a few hours.