[IAUC] CBET 1309: 20080320 : SUPERNOVA 2008ax IN NGC 4490

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                                                  Electronic Telegram No. 1309
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 2008ax IN NGC 4490
     S. Taubenberger and N. Elias-Rosa, Max Planck Institut fuer Astrophysik;
and A. Harutyunyan, H. Navasardyan and S. Benetti, INAF and Osservatorio
Astronomico di Padova, report that a series of spectrograms of SN 2008ax,
taken on Mar. 8.10, 16.92 and 18.04 UT with the Calar Alto 2.2-m telescope (+
CAFOS; range 320-890 nm), and on Mar. 13.99 with the Asiago 1.82-m telescope
(+ AFOSC; range 350-1000 nm), shows that the supernova has evolved strongly,
the shape of the continuum being significantly bluer in the later spectra.
Furthermore, He I features with blueshifts of 7000-9000 km/s (measured from
the absorption line minima) now dominate the spectrum (see also Chornock et
al., CBET 1298), but H-alpha is still present in absorption (blueshifted by
about 13500 km/s).  The strength of the Ca II near-infrared triplet,
initially very pronounced, has decreased considerably.  Assuming a recession
velocity of 589 km/s for the host galaxy of 2008ax (from The Updated Zwicky
Catalogue, http://tdc-www.harvard.edu/uzc/) the 'PASSparToo' comparison code
(evaluating the spectral features; Harutyunyan et al. 2005, ASP Conf. Ser.
342, 258) provides the best fit for the Mar. 18.04 spectrum with spectra of
the normal type-Ib supernova 1999dn, the hydrogen-rich type-Ib supernova
2000H, and the peculiar type-Ib/c supernova 2005bf at 3 days after, 7 days
after, and 25 days before B-band maximum, respectively (Benetti et al., in
preparation; Branch et al. 2002, Ap.J. 566, 1005; Folatelli et al. 2006,
Ap.J. 641, 1039).  Because of the weak hydrogen and dominant He I, SN 2008ax
appears as a type-Ib supernova, in agreement with the classification by
Marion et al. (CBET 1305) based on an infrared spectrum.


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                         (C) Copyright 2008 CBAT
2008 March 20                    (CBET 1309)              Daniel W. E. Green