2002IAUC.7989....1S

C. Sanchez-Fernandez, Research and Scientific Support Department, European Space Agency; C. Zurita and J. Casares, Instituto de Astrofisica de Canarias; A. J. Castro-Tirado, Instituto de Astrofisica de Andalucia; I. Bond, Mt. John University Observatory; and S. Brandt and N. Lund, Danish Space Research Institute, report: "We obtained time-series spectroscopy of the blackhole candidate XTE J1650-500 on June 10 using the UT4 telescope (+ FORS2) at the European Southern Observatory, Paranal. Fifteen spectra (range 575-731 nm; resolution 0.076 nm FWHM) showed a broad, double-peaked H-alpha emission line (EW = 1.0 nm) from the accretion disk and weak absorption lines from the companion star. Radial-velocity curves of the secondary star were measured by cross-correlation with several G/K-type template stars, all giving consistent results. A four-parameter sinusoidal fit to the secondary radial-velocity data was performed, yielding the following parameters for the best fit: period, 0.212 ± 0.001 days; semi-amplitude of the radial-velocity curve of the companion star, 309 ± 4 km/s; systemic radial velocity, 19 ± 3 km/s; T_0 = HJD 2452436.543 ± 0.001 day. The reduced chi**2 for the fit was 1.034. The resulting mass function for the compact object is then M_1(sin**3 i)/(1+M_2/M1)**2 = 0.64 ± 0.03 solar mass. If the more massive compact object is indeed a blackhole (i.e., M_1 > 3 solar masses), as indicated by the x-ray properties (IAUC 7707, 7715), and assuming a typical mass ratio of 0.1 for blackhole binaries, the inclination of the system must then be lower than 40 deg. The equivalent width of the H-alpha emission showed a about 40-percent modulation with the 0.21-day orbital period. The weakness of the absorption lines from the companion suggests that residual emission from the accretion disk still dominates the optical spectrum, and hence XTE J1650-500 had not yet reached true quiescence at the time of our observations."