The Long Period, High Latitude, Eclipsing Systems V748 Cen (= Cen X-4?) and BL Tel

Abstract

Extensive photoelectric photometry (Walraven system) as well as infra-red photometry and spectroscopy of V748 Cen (= S5003 Cen) are discussed. This object is found to be a binary showing total eclipses. The secondary is an M-type star. Gas streams in the system seem necessary to explain various aspects of the photometry as well as a shell absorption spectrum just before eclipse and a low excitation emission spectrum during totality. Infra-red photometry of BL Tel shows the presence of a cool secondary. This (M-type) star is probably larger than the supergiant F primary and the eclipses are partial. Complicating effects probably include an atmospheric eclipse by the secondary. The considerable distance of these systems from the galactic plane and their relation to such binaries as AR Pav and (nova) T CrB are briefly discussed. The possibility that the primary of V748 Cen like that of some related systems is highly evolved and that the heating effect of the gas stream was unusually strong near the epoch of the appearance of the transient (nova-like) X-ray source Cen X-4 makes the identification with this source at least plausible. There also seems to be some similarity of V748 Cen to the optical candidate for another transient X-ray source, 2U 1543–47.