Variable, optically thick plasma in the interacting binaries R Arae and HD 207739.

Abstract

Two close binaries observed with the IUE, R Ara and HD 207739, exhibit strong variations of spectral energy distribution that indicate the presence of variable, optically thick extrastellar gas. The deepening of the secondary (eclipse-like) minimum toward shorter wavelengths observed in the ultraviolet light curves of R Ara also provides additional strong evidence for the existence of inhomogeneous, optically thick extraneous plasma. The presence of absorption lines of Si IV, C IV, and N V indicates the existence of hotter gas than that implied by the B9 spectral type.