[IAUC] CBET 1242: 20080208 : SUPERNOVAE 2008U AND 2008X

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                                                  Electronic Telegram No. 1242
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVAE 2008U AND 2008X
     S. Blondin, Harvard-Smithsonian Center for Astrophysics (CfA), on behalf
of the CfA Supernova Group, reports that a spectrum (range 350-740 nm) of
2008U (cf. CBET 1238), obtained on Feb. 8.46 UT by M. Calkins with the F. L.
Whipple Observatory 1.5-m telescope (+ FAST), shows it to be either a
reddened type-IIn supernova or an outburst of a luminous blue variable (LBV).
The spectrum consists of a reddened continuum and narrow Balmer emission
lines (FWHM about 300 km/s), as well as other emission lines from the
underlying host galaxy.  The H_alpha emission line has a broader (FWHM about
3000 km/s) component not present in the other Balmer lines.  While this may
be the signature of a supernova-like event, adopting a recession velocity of
1948 km/s for the host galaxy (from The Updated Zwicky Catalog,
http://tdc-www.harvard.edu/uzc/), and assuming no peculiar motion, the
discovery magnitude of 18.4 corresponds to an absolute magnitude of roughly
-15, which is more consistent with an LBV than a supernova (cf. also SN
1997bs:  Van Dyk et al. 2000, PASP 112, 1532).
     Blondin et al. add that a spectrum (range 350-740 nm) of 2008X (cf.
CBET 1239), obtained as above on Feb. 8.43 UT by Calkins, shows it to be a
type-II-plateau supernova, 3-4 weeks past explosion.  Cross-correlation with
a library of supernova spectra using the "Supernova Identification" code
(SNID; Blondin and Tonry 2007, Ap.J. 666, 1024) indicates that 2008U is
most similar to the type-II-plateau supernova 2005cs at 3 weeks past
explosion.  Adopting a recession velocity of 3730 km/s for the host galaxy
of 2008U (from The Updated Zwicky Catalog), the maximum absorption in the
H_alpha line (rest 656.3 nm) is blueshifted by roughly 4000 km/s.


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                         (C) Copyright 2008 CBAT
2008 February 8                  (CBET 1242)              Daniel W. E. Green