Radial velocity of HD 77581 (Vela X-1) in the period of 1972 - 1983.

Abstract

The radial velocity of HD 77581 (Vela X-1 = 4U 0900-40) was derived from photospheric Fe Iv and Fe II lines observed by the International Ultraviolet Explorer (IUE) satellite in the period 1978-1983. No long-term variation in the radial velocity of 30 km/s was observed. It is shown that the absence of variation effectively rules out the possibility that the long-term variation of the pulse period of Vela X-1 is due to the Doppler effect of orbital motion of the HD 77581/Vela X-1 system around an unseen third body. The IUE radial velocity data are given in a table.