Central Bureau for Astronomical Telegrams
IAUC 6931: XTE J2012+381
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Circular No. 6931
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
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XTE J2012+381
A. Castro-Tirado, Laboratorio de Astrofisica Espacial y Fisica
Fundamental (LAEFF-INTA), Madrid, and Instituto de Astrofisica de
Andalucia, Granada; and J. Gorosabel, LAEFF-INTA, report:
"Following the detection of the x-ray transient XTE J2012+381 (IAUC
6920), U- and R-band images were taken on May 28.17 UT at the 2.2-m
telescope at the German-Spanish Calar Alto Observatory. The images
included the ASCA position reported on IAUC 6927. New U- and
R-band images were obtained on June 3.13 by N. Walton (Isaac Newton
Group of Telescopes, La Palma) at the 1.0-m Jacobus Kapteyn
telescope. No variable (by > 0.2 mag) source is seen when
comparing both images, down to a limiting magnitude of R = 21.5.
We note that a star of mag 18 is coincident (within 1") with the
variable radio source reported on IAUC 6924 and 6926."
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
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