Keck observations of the black-hole candidate GRO J0422+32

Keck observations of the black-hole candidate GRO J0422+32 in quiescence have been used by Filippenko, Matheson, & Ho (1995) to determine a mass function f(M-x) = 1.21 +/- 0.06 M. for the compact object. Reanalysis of the data shows that the mass ratio, q = M-c/M-x, is q = 0.116 +/- (0.079)(0.071) from the rotational broadening of the companion star v sin i = 90+/-(22)(27) km s(-1) (la). From q and the mass function (slightly revised to 1.13 +/- 0.09 M.), we derive the mass of the compact object, M-x = (1.4 +/- 0.2) sin-(3) i M.. The companion star (M2+/-(2)(1) spectral type) contributes 61 +/- 4% of the light at red wavelengths. An Ha! Doppler image of the system shows the typical ring-like distribution of an accretion disk. Emissivity laws for Her in black-hole binaries roughly follow an R-1.5 law, which is also supported dy GRO J0422+32. The Li I lambda 6708 absorption line is not detected (1 sigma equivalent width limit of 0.13 Angstrom), in contrast to four other X-ray binaries.