CYG X-3 - EVIDENCE FOR A BLACK-HOLE

We have observed time-variations in the profiles of several infrared e mission lines from the X-ray binary, Cyg X-3, which is believed to con sist of a Wolf-Rayet star and a compact object. We conclude that the v ariations are due to the orbital motion of the Wolf-Rayet star and der ive a mass function for Cyg X-3 of 2.3 M.. Assuming reasonable values for the mass of the Wolf-Rayet star and the inclination of the system, we obtain a range of masses 7-40 M. for the compact object, with a mo st likely value of 17 M.. This strongly suggests that the compact comp onent of Cyg X-3 is a black hole.