2011CBET.2711....2S

M. Stritzinger, Oskar Klein Centre, Stockholm University; N. Morrell, Las Campanas Observatory; and G. Folatelli, IPMU, University of Tokyo, report on spectra (range 360-1011 nm) of SN 2011cb taken on May 1.3 and 2.3 UT by B. Madore of the Carnegie Observatories. Both spectra were obtained at Las Campanas Observatory with the 2.5-m du Pont telescope (+ WFCCD), and they show that 2011cb is a type-IIb supernova. Comparison with a library of supernova spectra via the Supernova Identification tool (SNID; Blondin and Tonry, 2007, Ap.J. 666, 1024) shows that 2011cb is very similar to SN 1997dd as observed on 1997 Sept. 6 and that it also resembles other type-IIb events around maximum light. The spectra exhibit prevalent P-Cyg absorption lines associated with the the Balmer series and Ca II. Additional features related with He I are visible, most noticeably He I 587.6-nm, which is probably blended with Na I D. Features related to the Fe II multiplet 42 are also discernible. Adopting a host-galaxy recession velocity of 2366 km/s for PGC 69707 (Koribalski et al. 2004, A.J. 128, 16), expansion velocities of 13000 km/s and 12500 km/s for the first and second epochs, respectively, are obtained from the absorption minimum of H-alpha.