2011CBET.2786....1M

G. H. Marion, Harvard-Smithsonian Center for Astrophysics; J. Vinko, University of Szeged; and J. C. Wheeler University of Texas at Austin, report that a spectrum (range 420-1020 nm) of SN 2011ek (cf. CBETs 2783, 2785) was obtained on Aug. 9.41 UT with the 9.2-m Hobby-Eberly Telescope (+ Marcario Low Resolution Spectrograph) by S. Rostopchin. The velocities of Si II at 635.5 and 597.2 nm are higher than the usual value for subluminous (1991bg- like) type-Ia supernovae at similar epochs. Measured values of 13200 and 12900 km/s, respectively, are obtained, assuming a redshift of z = 0.005, as listed by NED (Rhee and van Albada 1996, A.Ap. Suppl. 115, 407) for the proposed host galaxy, NGC 918. The line-depth ratio for Si II absorption features at 635.5 and 597.2 nm [R(Si II)] is about 0.43, which is an intermediate value that lies between those of SNe 1992A (0.38) and 1986G (0.53) (Nugent et al. 1995, Ap.J. 455, L147). O I 777.3-nm and Ca II 857.9-nm produce very strong spectral features, and the continuum is flat – all of which are consistent with a 1991bg-like type-Ia supernova. Cross-correlation with a library of supernova spectra using the "Supernova Identification" code (SNID; Blondin and Tonry 2007, Ap.J. 666, 1024) shows that 2011ek is a type-Ia supernova near maximum light, but reasonable fits are found to templates from both normal and 1991bg-like type-Ia supernovae. The spectrum also shows a narrow, unresolved Na D feature (EW about 0.11 nm), suggesting significant reddening. The most recently reported brightness (mag 16.7 on Aug. 8.5; CBET 2785) is more than 4 magnitudes below the expected brightness for a normal type-Ia supernova at maximum.