IUE observations of the X-ray binary A0538-66 : spectroscopic study of a strange stellar system.

Abstract

The results of extensive IUE monitoring of the optical counterpart of the recurrent periodic LMC X-ray transient A0538-66 are presented. Even when the system is not in outburst dramatic spectral variations occur, accompanied by changes in the temperature and surface area of the continuum emitting region. It is shown that, in spite of these variations, the out-of-outburst data are consistent with constant bolometric luminosity. The optical outbursts can be powered solely by reprocessed X-rays. The long-term and orbital behavior of the system is discussed in the light of these results. From an analysis of apparently undisturbed P Cygni profiles, the mass-loss rate of the primary via its stellar wind is determined to be about 4 x 10 to the -9th solar masses/yr. Infrared photometry reveals an excess at H and K which is too large to be explained by free-free emission from this wind alone.