Progenitor masses of Type Ib/c supernovae

Recent models for the origins of Type Ib/c supernovae have proposed that the progenitors consist of relatively low-mass |(M ~ 12-18 M_)| stars in binary systems that have lost their hydrogen envelope. On the basis of the nickel mass, light curve and the amount of mixing, these models identify the low-mass end with Ic's and the higher mass end with Ib's. We shown that the dependence of the nickel mass on the progenitor mass is highly uncertain and suggest that the helium lines in Type Ib's and the lack thereof in Type Ic's could be more naturally explained by identifying the low-mass end with Ib's and the high-mass end with Ic's.