[IAUC] CBET 1774: 20090421 : VARIABLE STAR IN LIBRA

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                                                  Electronic Telegram No. 1774
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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CBAT en CFA.HARVARD.EDU (science)
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VARIABLE STAR IN LIBRA
     G. Pojmanski, D. Szczygiel, and B. Pilecki, Warsaw University
Astronomical Observatory, report a new apparent outburst of a variable that
was first discovered by the "All Sky Automated Survey" (ASAS) on 2003 July 23
and is located at R.A. = 15h09m46s, Decl. = -21o47'.7 (equinox 2000.0).
Three-minute CCD exposures taken with the ASAS3V instrument (70-mm-diameter,
200-mm f.l. f/2.8 telephoto lens + Johnson V filter; pixel size 14".8, rms
astrometric accuracy 4") yield the following V magnitudes:  2003 July 14.058
UT, 11.50; 15.155, 11.49; 23.071, 11.20; 25.189, 10.86; Aug. 2.034, 10.47;
7.069, 10.60; 11.040, 10.81; 21.049, 11.20; 25.003, 11.35; 27.005, 11.45;
Sept. 3.992, 11.47; 2009 Mar. 28.255, 11.55; 28.272, 11.48; 31.249, 10.93;
31.262, 10.95; Apr. 5.369, 10.38.  I-band exposures this month by Pojmanski
with the 1.3-m OGLE telescope suggest that this variable (designated ASAS
J150946-2147.7) is associated with the brighter of two close 2MASS sources:
2MASS J15094657-2147462 (J = 10.5, H = 10.4, K = 10.3).  Light curve and
images can be found at the following website URL:
http://www.astrouw.edu.pl/cgi-asas/asas_disc/150946-2147.7,4900,5000.
     K. Kinugasa, S. Honda, and O. Hashimoto, Gunma Astronomical Observatory
(GAO); and T. Kato, H. Maehara, and D. Nogami, Kyoto University, report that
they observed ASAS J150946-2147.7 with the GAO 1.5-m telescope (+ Gunma Low-
resolution Spectrograph, GLOWS; resolution about 400; range 400-800 nm) on
Apr. 7, 9, 10, and 15.  The spectra showed strong emission lines of He II at
468.6 nm, C III/N III at 464.0 nm, and weaker He I emission lines superimposed
on a late-A-type stellar spectrum.  These emission lines and stellar absorption
lines showed radial-velocity variations with measured amplitudes of about 110
km/s and 200 km/s (respectively) out of phase, suggesting that the emission
lines arise from an accretion disk around a black hole of 3-5 solar masses.
The ASAS J150946-2147.7 system is remarkably similar to the binary components
of the unusual microquasar V4641 Sgr (IAUC 7440; Orosz et al. 2001, Ap.J. 555,
489).  Since the large, superluminal 1999 outburst of V4641 Sgr (IAUC 7253,
7254, 7256, 7257, 7263, 7265, 7267) was preceded by enhanced optical activity
for months (IBVS 4777), the present active state might lead to a similar
giant outburst.  Close monitoring and observations at other wavelengths are
strongly encouraged.


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                         (C) Copyright 2009 CBAT
2009 April 21                    (CBET 1774)              Daniel W. E. Green