The X-ray source A0538 - 66 in optical quiescence

Photometric observations of A0538 - 66 in quiescence show that the optical star is an object of equivalent spectral type B7eII. Spectroscopic data taken simultaneously confirm this spectral classification and are consistent with the reported periodic variations seen in the emission lines. It is unlikely that the optical outburst is due to X-rays reprocessed in the atmosphere of the primary star or elsewhere. (author)