SN 1994I: Disentangling He I lines in Type Ic supernovae

We present spectroscopic observations of the Type Ic supernova SN 1994I and analyze the evidence for helium in the optical portion of the spectrum. The development of high-velocity He I lambda 5876 starting approximately 1 week after maximum light provides a pattern of evolution that can be used to discriminate He I lines in other Type Ic supernovae. We show that, contrary to earlier interpretation, SN 1987M displayed He I lines. The He abundance is, however, probably consistent with previously derived upper limits. We also identify He in SN 1988L. We conclude that most, and probably all, Type Ic supernovae show evidence for He I lines in the optical region of the spectra, which implies small amounts of high-velocity helium in the outer portions of the ejecta. The implications of this result for the progenitor stars are discussed.