Supernova 1996bu in NGC 3631

S. Nakano, Sumoto, Japan, communicates that Reiki Kushida, Yatsugatake South Base Observatory, reports her discovery on an unfiltered CCD image taken on Nov. 14.793 UT with a 0.40-m f/5 reflector of an apparent supernova (mag 17.3) located at R.A. = 11h20m59s.18, Decl. = +53 12'08".0 (equinox 2000.0; measurement by Y. Koshida), which is 32" west and 117" north of the center of NGC 3631. No star at this position is visible on her frames taken on 1996 Feb. 13 and May 9. P. Garnavich, P. Challis, and R. Kirshner, Harvard-Smithsonian Center for Astrophysics, report that C. Hergenrother and W. Brown obtained CCD images of SN 1996bu with the Whipple Observatory's 1.2-m reflector on Nov. 17.49 UT, yielding V = 17.6 and B = 18.1 and position end figures 59s.30, 08".4 for the supernova. Spectra obtained with the Multiple Mirror Telescope by R. Marzke and S. Odewahn on Nov. 18.5 show SN 1996bu to be a peculiar type-II supernova. Narrow Balmer emission lines are seen above a blue continuum; the continuum becomes flat shortward of 500 nm. The widths of the lines are 1400 km/s FWHM after correcting for the spectral resolution; at the base of the H-alpha emission, the full width increases to 5500 km/s. The H-alpha emission centroid is redshifted by 1140 km/s, which is close to the velocity of 1156 km/s for NGC 3631. There is no evidence of broad P-Cyg features seen in normal type-II supernovae. Deep absorption features of Na I 590.7-nm (0.4 nm equivalent width) and Ca II 395.7-nm (1.5 nm EW) are seen and may be due to interstellar or circumstellar gas.