[IAUC] CBET 878: 20070312 : SUPERNOVAE 2007ah AND 2007al

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                                                  Electronic Telegram No. 878
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 2007ah AND 2007al
     S. Blondin, M. Modjaz, R. Kirshner, and P. Challis, Harvard-Smithsonian
Center for Astrophysics, report that a spectrogram (range 350-740 nm) of
2007ah (cf. CBET 869), obtained by T. Groner on Mar. 12.18 UT with the F. L.
Whipple Observatory 1.5-m telescope (+ FAST), shows it to be a type-II
supernova roughly 1 week past explosion.  The spectrum consists of a blue
continuum and P-Cyg lines of the Balmer series, consistent with the plateau
phase of a normal type-II supernova.  The spectrum is similar to the type-
II-plateau supernova 1999em at 7 days past explosion.  Adopting a recession
velocity of 5747 km/s for the host galaxy (from Huchra et al. 1999, Ap.J.
Suppl. 121, 287), the maximum absorption in the H_alpha line (rest 656.3 nm)
is blueshifted by roughly 13000 km/s.
     Blondin et al. add that a spectrum (range 350-740 nm) of 2007al (cf.
CBET 875), obtained on Mar. 12.30 by Groner, shows it to be a type-Ia
supernova around maximum light.  Cross-correlation with a library of
supernova spectra indicates that 2007al is most similar to the subluminous
type-Ia supernova 1991bg at 3 days past maximum.  Adopting a recession
velocity of 3621 km/s (from Zabludoff and Mulchaey 1998, Ap.J. 496, 39) for
the host galaxy (whose 2MASX position is given as R.A. = 9h59m18s.7, Decl.
= -19d28m23s, equinox 2000.0), the maximum absorption in the Si II line
(rest 635.5 nm) is blueshifted by roughly 9500 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, similar to SN 1991bg at the same phase.


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                         (C) Copyright 2007 CBAT
2007 March 12                    (CBET 878)               Daniel W. E. Green