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IAUC 7989: XTE J1650-500; P/2002 S1

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                                                  Circular No. 7989
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
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XTE J1650-500
     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/M_1)**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."

     Additional observations and the following elliptical orbital
elements appear on MPEC 2002-S61:

     T = 2002 Mar. 26.5669 TT         Peri. =  35.6546
     e = 0.437531                     Node  = 347.4633  2000.0
     q = 2.305629 AU                  Incl. =  27.6887
       a =  4.099120 AU    n = 0.1187594    P =   8.299 years

                      (C) Copyright 2002 CBAT
2002 October 8                 (7989)            Daniel W. E. Green

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