SN-1994I IN M51 AND THE NATURE OF TYPE-IBC SUPERNOVAE

Early spectra of SN 1994I in M51 (NGC 5194) are presented along with a rguments that it is a member of the class of helium-poor Type Ic super novae. The issue of H and He in the spectra of Type Ib and Ic events i s reexamined with the conclusion that Type Ib eject substantially less H than even transition events like SN 1993J and that Type Ic eject su bstantially less He than Type Ib and their optical spectra are consist ent with no H or He. Type Ic show an absorption of the Si II lambda 63 55 blend that characterizes Type Ia. This feature requires only a sola r abundance of Si. Some Type Ic show an absorption that is probably C II lambda 6580. IR spectra are presented of SN 1990W which show the li ne of He I lambda 10830. The strength of this feature and the rather s low decay of the late time light curve suggest that this event could b e better classified as a Type Ib. Even if trace abundances of H are pr esent in Type Ib and of He in Type Ic the spectral differences still i mply a distinctly different evolution for the progenitors of Type Ib f rom both Type Ic and events like SN 1993J.