Are Wolf-Rayet Stars the Progenitors of Type IB/IC Supernovae?

I discuss evidence for and against the hypothesis that Type Ib and Type Ic supernovae (SNe) are produced by core collapse in massive, evolved progenitors. A key object is SN 1987K, whose spectroscopic classification changed from Type II to Type Ib/Ic as it aged. The progenitor of SN 1987K may well have been a massive star which experienced incomplete mass loss, leaving a thin outer envelope of hydrogen. However, several arguments are used to conclude that in most SNe Ib/Ic, the pre-supernova mass loss cannot be caused entirely by strong winds as in Wolf-Rayet stars. Mass transfer in close binary systems is probably important, but in such cases the supernova progenitor is not necessarily a Wolf-Rayet star; instead, it may be a relatively quiescent, hot, low-mass helium star that explodes via core collapse. For example, the rapid decline of the light curve of the Type Ic SN 1987M, and its seemingly low ejected mass, are consistent with this idea. It is also possible that some, but not all, SNe Ib/Ic arise from deflagrations or detonations of white dwarfs.