Mullard Space Science Laboratory

R. H. D. Corbet
Optical observations of binary x-ray sources

1984 (supervisor: J. L. Culhane)

A review is presented of the current state of observational and theoretical research into X-ray binaries.

A computer code has been developed to calculate the equipotential surfaces in a binary system including the effects of an eccentric orbit, radiation pressure and non-synchronous stellar rotation. This code is applied to several X-ray binaries and the problem of explaining the X-ray and optical light curves of GX301-2 is investigated.

Spectroscopic and photometric optical observations have been made of the galactic X-ray sources A0538-66, 2S0921-630 and 3A0726-260.

The recurrent X-ray transient A0538-66 was observed on two occasions, once whilst it was in an active state, and flares were occurring, and again when the system was inactive. During the ON state several different line components were present; their evolution throughout the outburst is discussed. During the OFF state H-Beta has an "inverse P-Cygni" profile. Radial velocity measurements during the OFF state show that A0538-66 is a highly eccentric system as previously suspected. A limit of 0.15% is placed on 69 ms optical pulsations during an outburst in May 1982.

The radial velocity curve of the HeII 4686 A emission line in the spectrum of 2S0921-630 confirms the 9 day period previously suggested for the system and excludes other candidate periods. Photometry shows that, contrary to previous reports, there is no well defined long duration eclipse of the B-band light. Models of the system are discussed.

A spectral map of 3A0726-260 is presented; the star is found to be of spectral type B0Ve and based on this classification a distance of 4.6 kpc is obtained.

A strong correlation is shown to exist between the orbital periods of binaries consisting of a Be and a neutron star and the spin period of the neutron star component. This relationship is explained as being caused by an equality of the Alfven and corotation radii of the neutron stars. It is demonstrated that this correlation makes possible the use of neutron stars as probes of the extended Be star atmosphere.


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