Central Bureau for Astronomical Telegrams
IAUC 7542: XTE J1118+480
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Circular No. 7542
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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XTE J1118+480
J. McClintock, M. Garcia, P. Zhao, N. Caldwell, and E. Falco,
Harvard-Smithsonian Center for Astrophysics, write: "Spectroscopic
observations of this x-ray nova were made with the new 6.5-m MMT on
Dec. 1 (two spectra) and 4 (six spectra). As expected, the spectra
contain both broad Balmer emission lines and the numerous
absorption features characteristic of a late-type dwarf. Robust
velocity measurements were obtained by cross-correlating the
individual spectra (range 490-650 nm) against the spectra of
several bright dwarfs (K5-M2). The eight velocities provide good
phase coverage and yield a velocity amplitude K = 698 +/- 11 km/s,
an orbital period P = 0.1701 +/- 0.0003 day (IAUC 7412, 7418), and
a time of maximum velocity on 2000 Dec. 1.4776 +/- 0.0005 UT. The
large value of the mass function, f(M) = 6.0 +/- 0.3 solar masses,
is rivaled only by that of V404 Cyg. Our Oct. 26 observations (V =
18.8; Whipple Observatory 1.2-m telescope) showed that the nova was
near its pre-outburst brightness (IAUC 7390). See also the
simultaneous Nov. 30-Dec. 1 photometry given below."
R. M. Wagner, LBT Observatory; C. B. Foltz, MMT Observatory;
S. G. Starrfield, Arizona State University; and P. Hewett,
Institute of Astronomy, Cambridge, report: "Thirteen optical
spectra (range 410-750 nm; resolution 0.35 nm) of XTE J1118+480
were obtained with the 6.5-m MMT on Nov. 20.40-20.48 and 30.36-
30.51 UT. Convolution of the average flux-calibrated spectrum
obtained on Nov. 20 with a V-band filter gives V = 19.0, comparable
to its pre-outburst quiescent brightness (IAUC 7390). The spectrum
exhibits broad (FWHM about 2400 km/s), double-peaked, Balmer
emission lines superposed on the spectrum of an M0-M1V star,
similar to other x-ray novae in their quiescent states. Cross-
correlation of the individual spectra with three bright, late-type
dwarf star spectra yields a sinusoidal variation in radial velocity
of the absorption lines with the following orbital parameters: K =
695 +/- 16 km/s, P = 0.1699 +/- 0.0001 day, T_0 = 2000 Nov. 20.392
UT +/- 0.045 day (corresponding to absolute phase 0.0 or inferior
conjunction of the dwarf star). The inferred mass function is 5.9
+/- 0.4 solar masses, suggesting that the compact object is a black
hole."
P. Garnavich, University of Notre Dame, monitored XTE
J1118+480 via 2-min I-band exposures for a total of 6 hr with the
1.8-m Vatican Advanced Technology Telescope on Nov. 30 and Dec. 1
UT: "The star was near quiescence at V = 18.8 (P. Groot, priv.
comm.). The light curve, phased to a period of 4.1 hr (Uemura et
al. 2000, PASJ 52, 15), shows a double sinusoidal variation with a
peak-to-peak amplitude of 0.15 mag, plus some additional flux at
phase 0.55 away from minimum light."
(C) Copyright 2000 CBAT
2000 December 15 (7542) Daniel W. E. Green
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