On the orbital evolution of Centaurus X-3.

The evolutionary history of the binary system containing Cen X-3 is investigated by considering the orbital evolution of the primary from the post-explosion stage to the present. Particular account is taken of the dependence of the system's orbital evolution on the adopted present rotational angular momentum of the primary. A scheme for analyzing the orbital evolution of a massive X-ray binary is outlined and applied to the Cen X-3 system, using several combinations of the component masses permitted by the uncertainty ranges obtained by Avni and Bahcall (1974). It is found that the track of orbital evolution depends critically on the value assumed for the ratio of the primary's present rotational angular momentum to the system's orbital angular momentum. The low galactic latitude of the system is shown to suggest strongly that the runaway velocity of the system is not very large. It is estimated that the runaway velocity is likely to be about 25 to 50 km/s, that the mass of the exploded star should have been about 3 to 4 solar masses, and that the rotational angular momentum of the primary should constitute a considerable fraction of the system's total angular momentum. It is suggested that the rotation of the primary is synchronous with the orbital motion.