Normal and peculiar type I supernovae - Why do they differ?

Bolometric luminosity curves calculated for two type I supernovae, the peculiar SN 1983n and the normal SN 1972e, indicate that the SN 1983 envelope has about 2.6 times as large an optical depth to gamma rays as SN 1972e. Constraints are placed on the mass and expansion velocity of peculiar relative to normal SN I envelopes; in particular, peculiar SN I's have a 2-3 time lower expansion velocity at the incineration-zone boundary. At epochs t greater than 40 days after maximum light, peculiar SN I spectra should exhibit strong emission lines representing unburned presupernova material; these lines are predicted to contribute about 40 percent of the overall optical luminosity. 17 references