SN 1994I in M51 and the nature of type IBC supernovae

Early spectra of SN 1994I in M51 (NGC 5194) are presented along with arguments that it is a member of the class of helium-poor Type Ic supernovae. The issue of H and He in the spectra of Type Ib and Ic events is reexamined with the conclusion that Type Ib eject substantially less H than even transition events like SN 1993J and that Type Ic eject substantially less He than Type Ib and their optical spectra are consistent with no H or He. Type Ic show an absorption of the Si II λ6355 blend that characterizes Type Ia. This feature requires only a solar abundance of Si. Some Type Ic show an absorption that is probably C II λ6580. IR spectra are presented of SN 1990W which show the line of He I λ10830. The strength of this feature and the rather slow decay of the late time light curve suggest that this event could be better classified as a Type Ib. Even if trace abundances of H are present in Type Ib and of He in Type Ic the spectral differences still imply a distinctly different evolution for the progenitors of Type Ib from both Type Ic and events like SN 1993J.