An Optical Outburst from the Periodic Recurrent X-Ray Transient A0538-66

Abstract

We present optical spectroscopy and photometry and IUE spectroscopy of the counterpart of the LMC recurrent X-ray transient A0538-66 during an outburst at the end of December 1980 which was consistent with the 16.6 day X-ray period (Skinner, 1980). The optical spectra show steadily increasing Balmer and HeI emission (indicative of a shell phase) superposed on a B2 IV spectrum with a substantial brightness increase of 2^m and the sharp turn-on of HeII λ686 at the peak. Significant radial velocity changes have been detected but they show no correlation with the 16.6 day period. IUE spectra during a subsequent outburst show very strong and broad (∼5000 km s^-1) emission from C IV λ1550 and HeII λ1640. This behaviour is compared with other galactic transients and shell/Be stars.