[IAUC] CBET 1337: 20080415 : SUPERNOVA 2008bt IN NGC 3404

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                                                  Electronic Telegram No. 1337
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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SUPERNOVA 2008bt IN NGC 3404
     S. Blondin, Harvard-Smithsonian Center for Astrophysics (CfA), on behalf
of the CfA Supernova Group, reports that a spectrogram (range 350-740 nm) of
2008bt (cf. CBET 1336), obtained by M. Calkins on Apr. 15.16 UT with the F.
L. Whipple Observatory 1.5-m telescope (+ FAST), shows it to be a type-Ia
supernova around maximum light.  Cross-correlation with a library of
supernova spectra using the "Supernova Identification" code (SNID; Blondin
and Tonry 2007, Ap.J. 666, 1024) indicates that 2008bt is most similar to the
sub-luminous type-Ia supernova 1991bg at 3 days past maximum.  Adopting a
recession velocity of 4551 km/s for the host galaxy (from Fairall et al.
1992, A.J. 103, 11), the maximum absorption in the Si II line (rest 635.5 nm)
is blueshifted by roughly 10300 km/s.  Assuming that the galaxy is in the
Hubble flow and the supernova suffers negligible extinction, the discovery
magnitude of 16.6 corresponds to an absolute magnitude of roughly -17.5,
comparable to SN 1991bg at the same age.  Also, interstellar Na I D
absorption at the redshift of the host galaxy is visible in the spectrum with
an equivalent width of 0.2 nm.


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                         (C) Copyright 2008 CBAT
2008 April 15                    (CBET 1337)              Daniel W. E. Green