Ultraviolet, optical and infrared studies of galactic binary x-ray sources

The central theme of this work is the study of the subclass of Galactic binary X-ray systems known as the Massive X-Ray Binaries (MXRB). The properties of these systems are first reviewed from an observational and theoretical standpoint, and contrasted with the related, though distinct, low-mass X-ray binary subclass. One of the most striking properties peculiar to the MXRB is that they exhibit regular X-ray pulsations. The UV flux of three of these systems has been examined to search for modulations over intervals corresponding to the known X-ray pulse periods. The IUE satellite was used for this purpose. As IUE was not designed for photometry of this sort, it was necessary to employ a special trailed observation mode in conjunction with specific data analysis techniques designed to optimise the sensitivity and temporal resolution available. These procedures, which should be applicable to other similar research programmes, are described in detail. The UV spectrum of the sources Vela X-1, A0535+ 26 and 4U1145-619 were sampled with a resolution of ∼1/10th of the respective pulse periods. Modulations of 15-20% were observed from Vela X-1 on two occasions, for which it is concluded that an intrinsic variation in the flux from the supergiant B0.5Ib companion is the most likely explanation. Only one observation of A0535 + 26 was made, but the finding of a modulation of 10-15% is more compelling: because of the manner in which the image was obtained, the modulated UV component requires an explanation in terms of reprocessed X-rays or possibly (though less plausibly) direct emission from the vicinity of the neutron star. Modulation of the UV signal from the 4U1145-619 system is excluded at the 5% level. The remainder of this work deals with new observations of the proposed counterparts of three hard X-ray transients; in all three cases it is shown that the most likely counterpart has a spectrum consistent with that of a Be star. The first UV spectrum of the A1118-616 system is presented, and is consistent with a 25,000±5000K star reddened by E_B-V= 0.9±0.1. IR observations of the V0332 + 53 transient over a 28-month period following an X-ray outburst are reported which show the flux to be declining. The behaviour of the Hα emission is also found to be partly correlated with the IR decline; both are accounted for by the expulsion of a shell of material from the companion star. The latter is a late Oe/early Be type with TEFF≃30,000K displaying local plus interstellar reddening of E_B-V= 1.95±0.05. Finally the optical/IR counterpart of the EXO 2030 + 375 system is identified. It is shown that the candidate previously proposed (Robin et al., 1985) is erroneous. (D80425)