Hydrogen in type Ic supernovae?

By definition, a Type Ic supernova ( SN Ic) does not have conspicuous lines of hydrogen or helium in its optical spectrum. SNe Ic are usually modeled in terms of the gravitational collapse of bare carbon-oxygen cores. We consider the possibility that the spectra of ordinary ( SN 1994I - like) SNe Ic have been misinterpreted, and that SNe Ic eject hydrogen. An absorption feature usually attributed to a blend of Si II lambda 6355 and C II lambda 6580 may be produced by Ha. If SN 1994I - like SNe Ic eject hydrogen, the possibility that hypernova ( SN 1998bw - like) SNe Ic, some of which are associated with gamma-ray bursts, also eject hydrogen should be considered. The implications of hydrogen for SN Ic progenitors and explosion models are briefly discussed.