UV Observations of Three LMC Be-Star/X-ray Binaries

This paper describes IUE ultraviolet observations of three Be-star/X-ray binaries in the LMC: CAL 9, CAL E, and RX J0520.5-6932. Because the optical spectra show evidence of an overlying continuum source, ultraviolet spectra were obtained to further investigate its properties, but no UV emission lines are found. The UV spectra have been compared to models indicating that the stellar temperatures are near 30000 K (for log g = 4.0). This is in agreement with the temperatures suggested by the spectral type determined in the optical region. Thus, there is no clear evidence in either the optical or UV regions of the gas being accreted by the unseen compact companion which must give rise to the X-ray emission. Optical photometry shows these systems undergo irregular variations of up to a few tenths of a magnitude.