Simultaneous ultraviolet, optical and X-ray observations of the X-raysource Vel X-1 (HD 77581).
Davis, R. J.; Raymond, J. C.; Hammerschlag-Hensberge, G.; Dupree, A. K.; Lamers, H. J. G. L. M.; Black, J. H.; Watson, M.; van den Heuvel, E. P. J.; Burger, M.; Whitelock, P. A.; Sanford, P. W.; Morton, D. C.; Hartmann, L.; Menzies, J. W.; Gursky, H.; De Loore, C.; Vanden Bout, P. A.; van Dessel, E. L.; Matilsky, T.; Pollard, G. S. G.
United States, Netherlands
Abstract
UV spectra (obtained by the IUE) of HD 77581, associated with the binary X-ray source Vela X-1, show a spectrum typical of an early B-type supergiant. However, the P Cygni profiles of strong resonance lines show substantial variations with orbital phase. These variations can be ascribed to the changing ionization state in the stellar wind caused by the X-ray emitting companion. X-ray and spectroscopic and photometric optical observations, simultaneous with the IUE observations, indicate behavior consistent with previous epochs.