Mullard Space Science Laboratory

G. E. Parkes
A study of the optical counterparts of Galactic X-ray sources

1979 (supervisor: J. L. Culhane)

Optical spectroscopy at the 3.9m Anglo-Australian telescope has revealed the optical counterparts of two compact Galactic X-ray sources, 4U 1258-61 and 4U 1538-52. High resolution spectral studies of these and the previously identified counterparts of 4U 1145-61 (star HEN 715) and 4U 1223-62 (star WRAY 977) are used to accurately assess the spectral types and hence masses, radii and luminosities of the primary stars in their pulsating X-ray systems. All four are massive early-B stars which are losing mass.

Velocity progressions along series of absorption lines in the spectrum of WRAY 977 and asymmetrical absorption line profiles in the spectrum of the 4U 1538-52 primary indicate that both these supergiant stars have expanding and accelerating atmospheres. WRAY 977 and the dwarf star HEN 715 are examined for spectral variability. Changes in the asymmetrical H_alpha emission from HEN 715 indicate considerable activity in the atmosphere of this star.

The newly discovered optical counterpart of 4U 1258-61 is a shell star. The sharp, deep absorption lines in the spectrum are probably formed in a dense extended envelope (or shell). The size of this envelope is estimated from the H_alpha emission profile. Rotationally broadened stellar lines underlying the shell lines at H_gamma and H_beta indicate that the star is an early-B dwarf rotating at close to instability.

The interstellar spectra of the four stars are examined, and the distances and hence X-ray luminosities of each system estimated. Mass loss rates from the primary stars and source models are discussed.

An optical spectrum of the faint blue star associated with 4U 0614+09 is presented. This X-ray source is one of a class of objects which are probably fundamentally different in nature to the massive X-ray binaries. The models are discussed.


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