Subject: IAUC 6931: XTE J2012+381
From: quai@cbatmpc (IAUC mailing list)

Circular No. 6931
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XTE J2012+381
     M. R. Garcia, J. E. McClintock, and E. Barton,
Harvard-Smithsonian Center for Astrophysics; and P. Callanan,
University College, Cork, report:  "On June 1.45 UT, we obtained an
optical spectrum of the USNO A1.0 star 1275.13846761, which is
within about 1".3 of the variable radio source (IAUC 6924, 6926),
and in turn may be related to the x-ray transient XTE J2012+381
(IAUC 6920, 6922).  Preliminary reduction of the 20-min exposure
with the Whipple Observatory 1.5-m telescope (+ FAST spectrograph;
0.3-nm resolution, range 400-700 nm) shows a nearly featureless red
continuum.  The only clearly identifiable lines are H-beta, H-gamma,
and Na D in absorption; a strong night sky line at H-alpha makes it
difficult to determine the intrinsic H-alpha profile.  The upper
limit to the equivalent width of any possible He II 468.4-nm
emission is about 0.1 nm.  A cross-correlation with the Jacoby
stellar atlas indicates a spectral type of F3 +/- 3 subclasses for
a dwarf, or F0 +/- 6 subclasses for a giant.  CCD photometry with
the Whipple Observatory 1.2-m telescope on May 28.31 yields B =
19.35 +/- 0.1, V = 18.1 +/- 0.1, indicating B-V = +1.25.  The
photometry and spectroscopy are consistent with an absorption A(V)
= 2.8, and an F3 dwarf at about 3 kpc or an F0 giant at about 6
kpc.  These results neither confirm nor refute the possible
association of this star with the x-ray nova.  If this star is the
counterpart, it could be similar to the F-giant companion of Cyg
X-2, which shows weak (equivalent width about 0 to 0.3 nm) and
variable He II 468.6-nm emission, and sometimes an absence of
H-Balmer emission.  Alternatively, the star could be a chance
coincidence along the line of sight, similar to the case of GX 17+2."

                      (C) Copyright 1998 CBAT
1998 June 4                    (6931)            Daniel W. E. Green