THE ORIGIN OF SUPERNOVAE WITH DENSE WINDS

A family of type II supernovae with signatures of a dense circumstella r wind with an outflow rate M > 10(-4)u(10) (where u(10) is the wind v elocity in units of 10 km/s) is identified. The relative occurrence la te of these supernovae (designated type IIdw) is estimated to be 0.05 of the rate of all type II supernovae. The anomalous IIdw spectra are described using qualitative models involving a collision with either a smooth or a clumpy wind. The main properties of these supernovae are summarized. An analysis of the deceleration of the envelope of SN 1979 C indicates the ejected mass to be approximate to 2 M., which is consi stent with IIdw supernovae having relatively low masses. Two possible origins for IIdw supernovae are considered: (1) intense mass loss from a binary system that is embedded in a common envelope. (2) a superwin d from a single star. The IIdw/II ratio predicted by the first model i s too low (approximate to 10(-3)), and this model must therefore be re jected. The second mechanism can work if IIdw supernovae are hem of st ars with some interval of initial masses Delta M-ms approximate to 1 M . at the boundary for intermediate mass stars-i.e., stars with masses M-ms similar to 8-10 M.. The superwind model predicts a low mass for I Idw envelopes and a low abundance of oxygen and Ni-56. Some IIdw super novae may have a narrow optical maximum and low luminosity at the radi oactive stage. The case of a moderate-density wind may con correspond to SN 1987B-type supernovae, which show signatures of interaction with a wind and have relatively low luminosity.