[IAUC] CBET 915: 20070408 : SUPERNOVAE 2007bc AND 2007bd

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                                                  Electronic Telegram No. 915
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 2007bc AND 2007bd
     S. Blondin, M. Hicken, M. Modjaz, R. Kirshner, and P. Challis,
Harvard-Smithsonian Center for Astrophysics, report that spectra (range
350-740 nm) of 2007bc (cf. CBET 913) and 2007bd (cf. CBET 914), obtained
on Apr. 7.26 and 7.19 UT by P. Berlind with the F. L. Whipple Observatory
1.5-m telescope (+ FAST), shows them to be both type-Ia supernovae.
Cross-correlation with a library of supernova spectra shows that 2007bc
is most similar to SN 1998bu at three days before maximum light, and that
2007bd is most similar to SN 1992A (Kirshner et al. 1993, Ap.J. 415, 589)
at five days before maximum.  Adopting a recession velocity of 6236 km/s
for the host galaxy of 2007bc (from "The Updated Zwicky Catalog",
http://tdc-www.harvard.edu/uzc/), the maximum absorption in the Si II line
(rest 635.5 nm) is blueshifted by roughly 10500 km/s.  The cross-correlation
redshift for 2007bd is cz = 9300 +/- 1200 km/s, consistent with the value
given in "The Updated Zwicky Catalog" (9299 +/- 65 km/s) and inconsistent
with that reported by de Vaucouleurs et al. (1991, Third Ref. Cat. of Bright
Galaxies; 1347 +/- 54 km/s).  Adopting the former value for the recession
velocity of the host galaxy of 2007bd, the maximum absorption in the Si II
line (rest 635.5 nm) is blueshifted by roughly 15500 km/s.


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                         (C) Copyright 2007 CBAT
2007 April 8                     (CBET 915)               Daniel W. E. Green