Rayleigh-Taylor instabilities and mixing in the helium star models for Type Ib/Ic supernovae

Abstract

Motivated by the necessity of large-scale mixing in modeling the light curves of Type Ib/Ic supernovae (SN Ib/Ic), the Rayleigh-Taylor (R-T) instabilities in exploding helium stars of masses M(alpha) = 3.3, 4, and 6 solar masses are calculated for the first time with a two-dimensional hydrodynamical code. Mixing of the ejected material induced by the instabilities is found to be more extensive for smaller mass stars. For M(alpha) less than about 4 solar masses, Ni-56 is mixed to the outermost helium envelope. For M(alpha) greater than about 6 solar masses, on the contrary, the growth of the R-T instability is too weak to convey Ni-56 into the outer layers. The extensive mixing in smaller mass stars is consistent with the early light curve models for SN 1983N (Type Ib) and SN 1987M (Type Ic) whose declines are as fast as and even faster than Type Ia supernovae. On the other hand, no significant mixing for larger M-alpha may be consistent with the slow decline of SN Ib 1984L. Thus the observed variation of the SN Ib/Ic light curves can naturally be accounted for by the variation of mixing as a function of the helium star mass. 29 refs.