On the occurrence of streams and disks in massive X-ray binary systems

It is argued that the companion stars in the massive X-ray binaries Cyg X-1, Cen X-3, SMC X-1, 3U 1700-37, and 3U 0900-40 are expected to fill their critical lobe and lose mass by means of both a strong stellar wind and a stream from the surface point closest to the compact object, with the stream trajectory strongly depending on the rotation rate of the companion. Some consequences of mass loss via a stream are investigated for the formation of accretion disks and the occurrence of absorption features in X-ray light curves. It is shown that most of the accreted matter is likely to be captured from a stream in Cen X-1, SMC X-1, and Cyg X-1 in its high state, while the compact objects in 3U 1700-37 and 3U 0900-40 apparently accrete only from a stellar wind and do not have accretion disks around them. It is suggested that: (1) not every massive X-ray binary needs to have an accretion disk, but the occurrence of a disk in such systems is by no means excluded; (2) lobe-overflow streams are likely to be the cause of the absorption features observed in the X-ray light curves of the five systems; and (3) the companions in massive X-ray binaries are usually very slow rotators.