Electronic Telegram No. 1408
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
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SUPERNOVA 2008cw
     S. Blondin, Harvard-Smithsonian Center for Astrophysics (CfA), on behalf
of the CfA Supernova Group, reports that a spectrum (range 320-840 nm) of
2008cw (cf. CBET 1395), obtained on June 6.38 UT by P. Challis with the MMT
6.5-m telescope (+ Blue Channel spectrograph), shows it to be a type-IIb
supernova around one week past maximum light.  SN 2008cw was classified as a
peculiar type-Ib supernova, similar to SN 2005bf, by Yuan et al. on CBET 1395.
Cross-correlation with a library of supernova spectra using the "Supernova
Identification" code (SNID; Blondin and Tonry 2007, Ap.J. 666, 1024) indicates
that 2008cw is most similar to the type-IIb supernova 1993J at four days past
maximum light.  The top 50 comparison spectra that yield a good correlation
with 2008cw all belong to type-IIb supernovae.  Blueshifted absorption
features due to H_alpha and H_beta are clearly seen in the spectrum, as are
conspicuous lines of He I (rest 587.6, 667.8, 706.5 nm), characteristic of
type-IIb supernovae.  Specifically, a P-Cyg profile due to He I (rest 667.8
nm) overlaps with the H_alpha emission profile to create a broad, double-
peaked emission feature.  A recession velocity of cz = 9724 +/- 38 km/s is
derived using 12 emission lines in the host-galaxy spectrum, consistent with
the redshift reported by Yuan et al. (z = 0.032; i.e., cz approximately 9590
km/s).  Adopting this recession velocity for the host galaxy of 2008cw, the
maximum absorption in the H_alpha line is blueshifted by roughly 11000 km/s.
Furthermore, several other spectra (range 350-740 nm), obtained between June
4.29 and 11.23 UT by E. Falco, M. Calkins, and P. Berlind with the F. L.
Whipple Observatory 1.5-m telescope (+ FAST), confirm the classification of
2008cw as a type-IIb supernova.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
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                         (C) Copyright 2008 CBAT
2008 June 17                     (CBET 1408)              Daniel W. E. Green