Electronic Telegram No. 3136
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
CBAT Director:  Daniel W. E. Green; Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau@eps.harvard.edu (alternate cbat@iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


NOVA SCORPII 2012
     R. M. Wagner, Ohio State University (OSU) and Large Binocular Telescope
Observatory; S. Dong, Institute for Advanced Study, Princeton; T. Bensby,
Lund Observatory; J. Prieto, Princeton University; I. Bond, Massey
University; P. Tristram, Mt. John University Observatory; D. Bennett,
University of Notre Dame; K. Wada and T. Sumi, Osaka University, and the
Microlensing Observations in Astrophysics (MOA) collaboration; A. Gould,
OSU, and the Microlensing Follow-Up Network (microFUN) collaboration; and
S. Starrfield, Arizona State University, report the discovery and initial
photometry and spectroscopy of a bright transient in the direction of the
Galactic bulge.  The MOA collaboration detected a candidate microlensing
event, designated MOA 2012 BLG-320, on 2012 May 22.80 UT at magnitude
I = 18.5, located at R.A. = 17h50m53s.90, Decl. = -32d37'20".5 (equinox
2000.0).  No significant source appears at this position on either the R
or N survey plates of the Digitized Sky Survey.
     MOA photometry of the source before the outburst shows that the
progenitor was at I magnitude about 19.0-19.5, but with substantial
variability on nightly time scales.  Between May 14 and 16 UT, the source
began a slow monotonic increase in brightness, and after May 24 UT, the
rate increased significantly.  The light curve obtained between May 28 and
31 UT exhibits periodic modulations with an amplitude of about 0.1 mag and
a period of about 1.6 hr superposed on the brightening source.  Between
June 1.77 and 2.55 UT, the transient brightened dramatically from I magnitude
about 17, reaching I magnitude about 11 on June 3.33 UT -- prompting more
detailed follow-up by both MOA and the microFun collaborations.
    On June 4.08 UT, a high-resolution optical spectrum (range 375-950 nm;
resolution R = 42000) of the transient was obtained with the Very Large
Telescope (+ UVES).  The spectrum exhibits strong emission lines with
striking P-Cyg profiles of the Balmer series of hydrogen and many multiplets
of Fe II, as well as O I 777.4- and 844.6-nm.  The equivalent widths of both
H-beta emission and absorption are 1.7 and 0.3 nm, respectively.  The
interstellar Na D lines are resolved and exhibit considerable structure at
this spectral resolution.  The total equivalent widths of the D1 and D2
lines are 0.16 and 0.19 nm, respectively.  The spectrum is reminiscent of
either a slow "Fe II-type" classical nova or an intermediate-luminosity red
transient like V838 Mon.  However, the measured H-beta and H-alpha FWHM of
about 800 km/s (average expansion velocity of about 400 km/s) are more
consistent with slow classical novae that have t_2 around 50-200 days and
are thermonuclear events on accreting white dwarfs.  Other historical slow
novae include V450 Cyg and HR Del, which were observed to have comparable
expansion velocities and t_2 of 90 and 150 days, respectively.
     The most recent photometry of this new nova obtained on June 7.29, from
images obtained with the Cerro Tololo 1.3-m telescope (+ ANDICAM) are
magnitudes V = 11.6 and I = 9.4.  The transient continues to brighten at a
rate of about 0.4 mag/day in the I band over the past three nights.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2012 CBAT
2012 June 8                      (CBET 3136)              Michael Rudenko