THE MASS OF THE BLACK-HOLE IN GS2000+25 (=QZ VUL)

We report the first infrared light curve of GS 2000 + 25. By modelling the brightness variations as ellipsoidal modulations of the secondary star, we find the mass of the compact object to lie between 4.8 and 1 4.4 M. (90 per cent confidence) for secondary masses less than or equa l to 0.7 M.; this result is independent of the mass ratio, q. The uppe r inclination limit of the system is more dependent on q, although the lower inclination limit is almost independent of it, and for q = 20 w e find the inclination of the system to lie between 43 degrees and 69 degrees.