2008CBET.1309....1T

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.