On the mass of the black hole in GS 2000+25

We present J- and K'-band (1.95-2.35 mu m) photometry of the quiescent X-ray nova GS 2000+25, obtained in an attempt to constrain the mass of the compact object (M(X)). Combined with the mass function of 4.97 M(.), the infrared light curves imply M(X) less than or equal to 11 M(.) (90% confidence level), regardless of the evolutionary state of the secondary, for a mass ratio q of 4 < q < 30. For a secondary mass in the range M(2) = 0.4-0.9 M(.) (as expected for a K dwarf companion), and assuming a negligible contribution from the disk at these wavelengths, we find M(X) = 8.5 +/- 1.5 M(.) and an inclination of 65 degrees +/- 9 degrees. The observed infrared color is consistent with that expected of a K dwarf secondary. If the accretion disk continuum is given by f(lambda) proportional to lambda(-1.8), as observed in other quiescent X-ray novae, we constrain the accretion disk contribution to the K' flux (independently of optical estimates) to less than or equal to 12%.