EARLY-TIME SPECTRA OF TYPE-IC SUPERNOVAE - FURTHER EVIDENCE FOR THE PRESENCE OF HYDROGEN

Comparison of the early-time optical spectra of the Type II SN 1985L and the Type Ic SN 1987M confirms the previously suspected presence of H-alpha in SN 1987M. The H-alpha line has a P Cygni profile in both objects, but it is not as prominent as in the Type II SN 1987K, whose spectrum at late times became indistinguishable from that of SNs Ic. A spectrum of the Type Ic SN 1991A reveals a weak but nearly unmistakable H-alpha emission line; faint H-alpha emission may also be present in the Type Ic SN 1990aa. These observations support the hypothesis that SNs Ic and SNs II are physically related, with the main variable being the amount of hydrogen in the outer envelope. The fact that O I lambda-7774 absorption is strong in the early-time spectra of SNs Ic, but absent in the corresponding spectra of SNs II, may be consistent with this hypothesis. However, the data do not yet conclusively eliminate white dwarf models for SNs Ic.