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IAUC 7407: XTE J1118+480; 1999gv

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                                                  Circular No. 7407
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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XTE J1118+480
     C. A. Haswell, Open University; R. I. Hynes, Southampton
University; and A. R. King, Leicester University, on behalf of a
larger collaboration, report that Hubble Space Telescope
observations of XTE J1118+480 were made during Apr. 8.52-8.81 UT:
"Preliminary reductions reveal a flux density at 150 nm of 3 x
10**-13 erg cm**-2 s**-1 A**-1 with a continuum slope from 115 to
800 nm somewhat flatter than the nu**1/3 power law expected for a
viscously heated blackbody accretion disk.  This may suggest that
the intrinsic x-ray flux is relatively low, removing the motivation
for suggesting a nearly edge-on viewing angle (IAUC 7392).  The
Balmer jump appears in absorption.  N V emission (124.0, 124.3 nm)
is most prominent, with FWHM 1.4 nm and equivalent width 0.6 nm.
Si IV (139.4, 140.3 nm) and He II (164.0 nm) are also seen with
equivalent widths of 0.15 and 0.25 nm, respectively.  Lyman-alpha
absorption is apparent with full width likely > 10 000 km/s, which
is suggestive of a massive accretor.  No C IV or O V emission is
detected, suggesting that the accreting material has been CNO-
processed.  The indicated evolutionary scenarios, coupled with the
suggested 0.17-day orbital period (IAUC 7397), would make a primary
of mass > 3 solar masses unlikely.  J. Stull, Z. Ioannou, and N. A.
Webb obtained V-band photometry from the 0.8-m Stull Observatory
telescope at Alfred University during Apr. 13.05-13.35.  These data
appear inconsistent with a 0.17-day period, suggesting instead a
modulation at approximately twice this period.  In this case, the
0.17-day modulation might suggest nodal precession of a tilted disk
with period approximately half the orbital period
(http://xxx.lanl.gov/abs/astro-ph/?0004159).  A 0.34-day period
would remove the restriction to low-mass primaries referred to
above.  Further satellite observations are scheduled for Apr. 26-
May 1 and May 4.  Exact timings are given at
     O. Taranova and V. Shenavrin, Sternberg Astronomical
Institute, report the following mean infrared magnitudes of XTE
J1118+480 obtained during Apr. 12-15 with the 1.25-m telescope (+
InSb photometer) at the Crimean Station of the Sternberg
Astronomical Institute:  J = 12.4 +/- 0.2; H = 11.9 +/- 0.1; K =
10.9 +/- 0.1; L = 9.2 +/- 0.1.

Corrigendum.  On IAUC 7405, line 5, for  'broad B'  read  'broad R'

                      (C) Copyright 2000 CBAT
2000 April 26                  (7407)            Daniel W. E. Green

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