[IAUC] CBET 3187: 20120721 : SUPERNOVA 2012dt IN NGC 309 = PSN J00563888-0954091

Sab Jul 21 15:45:07 ART 2012

                                                  Electronic Telegram No. 3187
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 en eps.harvard.edu (alternate cbat en iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


SUPERNOVA 2012dt IN NGC 309 = PSN J00563888-0954091
     Greg Bock, Windaroo, Queensland, Australia, reports the discovery of an
apparent supernova (red mag 18.1) by Stuart Parker (Oxford, Canterbury, New
Zealand) on a 30-s unfiltered CCD image taken on July 17.54 UT with a 28-cm
Celestron C11 reflector (+ ST10 camera).  The new object is located at R.A. =
0h56m38s.88, Decl = -9d54'09".1 (equinox 2000.0; reference stars from USNO-B
and UCAC3 catalogues; measured by Bock), which is 50" west and 48" north of
the nucleus of the galaxy NGC 309.  Nothing is visible at this position on
Digitized Sky Survey red and infrared images (limiting mag > 19).  The variable
was designated PSN J00563888-0954091 when it was posted at the Central Bureau's
TOCP webpage and is here designated SN 2012dt based on the spectroscopic
confirmation reported below.  Additional magnitudes for 2012dt:  June 30, [18.5
(Parker); July 18.768, 18.3 (J. Brimacombe, Cairns, Australia, 41-cm RCOS
telescope + infrared filter; bandpass > 700 nm); July 19.096, 18.4 (F. Luppi
and L. Buzzi, Varese, Italy, 0.38-m f/6.8 reflector; position end figures
38s.85, 09".7; reference stars from CMC-14 catalogue; image posted at website
URL http://www.astrogeo.va.it/pub/TOCP/PSN_N309.jpg); 20.425, 18.0 (Brimacombe;
luminance filter inferred; position end figures 38s.85, 09".3; image posted at
URL http://www.flickr.com/photos/43846774@N02/7613256578/).  Brimacombe's July
18 image is posted at URL http://www.flickr.com/photos/43846774@N02/7600273288/.
The type-IIb supernova 2008cx also appeared in NGC 309 (cf. CBET 1399).

     J. T. Parrent, Las Cumbres Observatory Global Telescope (LCOGT) and
Dartmouth College; and D. A. Howell, LCOGT and University of California at
Santa Barbara report that a CCD spectrogram (range 390-950 nm) of PSN
J00563888-0954091 = SN 2012dt, taken with the Gemini Multi-Object Spectrograph
(GMOS) on the 8-m Gemini North telescope on July 19.2 UT, shows that it is a
type-IIP supernova several weeks after maximum light.  A recession velocity of
5780 km/s is inferred from the emission lines of the host galaxy, NGC 309.
Correcting for this redshift, the minimum of the H_alpha 656.3-nm absorption
feature is found to be blue-shifted by about 7400 km/s.  Comparisons to other
spectra with "Superfit" (Howell et al. 2005, Ap.J. 634, 1190) show similar
overlap with SN 1999em.

     Kate Maguire, Department of Physics, University of Oxford, writes that a
spectrogram of PSN J00563888-0954091 = SN 2012dt, obtained on July 20.5 UT
with the Double Beam Spectrograph on the Palomar 5-m telescope, shows broad
P-Cyg H_alpha emission with a velocity (half-width) of 1600 km/s and absorption
minimum at 8084 km/s.  Running the "Superfit" software yields a best match
to the spectrum of the type-II supernova 1999em at +9 days.


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

                         (C) Copyright 2012 CBAT
2012 July 21                     (CBET 3187)              Daniel W. E. Green