Electronic Telegram No. 2575
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


SUPERNOVA 2010ko IN NGC 1954
     P. Challis, G. H. Marion, and R. Kirshner, Harvard-Smithsonian Center for
Astrophysics (CfA), on behalf of the CfA Supernova Group, report that a
spectrum (range 340-740 nm) of the supernova candidate in NGC 1954 (cf. CBETs
2569, 2570) was obtained on Dec. 7 UT by M. Calkins with the F. L. Whipple
Observatory 1.5-m telescope (+ FAST).  Cross-correlation with a library of
supernova spectra using the "Supernova Identification" code (SNID; Blondin and
Tonry 2007, Ap.J. 666, 1024) shows the best fit for 2010ko is with the type-Ia
supernova 1992A at a phase of five days before maximum brightness.  The
velocity of the Si II 635.5-nm feature, measured at the absorption minimum, is
11900 km/s.

     J. Parrent, D. A. Howell, P. E. Nugent, M. Sullivan, and D. Murray, on
behalf the "Palomar Transient Factory", confirm the discovery of this supernova
in NGC 1954.  A CCD spectrum (range 350-950 nm) was taken with the Gemini South
telescope on Dec. 7 UT.  Matches to other spectra using "Superfit" (Howell et
al. 2005, Ap.J. 634, 1190) indicate that 2010ko is a type-Ia supernova close to
or before maximum light at an approximate redshift of z = 0.01.  Assuming this
redshift, the absorption minimum of the Si II 635.5-nm line displays a blue-
shifted velocity of 11400 km/s.  Further inspection of the spectrum reveals a
stronger-than-normal Si II 580-nm absorption line, similar to those observed in
subluminous type-Ia supernovae.  If 2010ko is subluminous, an apparent absence
of Ti II lines near 420 nm suggests that the supernova is only slightly sub-
luminous.  A Palomar image taken on Dec. 2.27 shows 2010ko at magnitude R =
17.5 +/- 0.3 (with respect to USNO-B1-catalogue data).


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2010 CBAT
2010 December 8                  (CBET 2575)              Daniel W. E. Green