TYPE-II-L SUPERNOVAE - STANDARD BOMBS

A method for deriving supernovae (SNs) luminosity functions is presented and it is used to derive the luminosity distribution of Type II SNs with "linear" light curves (SN II-L's). The luminosity function (of the absolute B-magnitude at maximum) can be represented by a Gaussian centered on M(B) = -16.45 (for H0 = 75 km s-1 Mpc-1) with a 1-sigma dispersion of only +/- 0.3 mag and a few higher luminosity SNs. The scatter about the mean is consistent with the uncertainties in the apparent B-magnitude at maximum and in the distances to the host galaxies. This suggests that there is little or no intrinsic scatter in the absolute B-magnitude at maximum and therefore that the majority (90%) of SN II-L's are very good standard bombs. There is a definite complete lack of low-luminosity SN II-L's. This and the small scatter about the mean, implies that the reddening around SN II-L's cannot be large. A weak correlation between absolute magnitude of the SNs and the inclination of the galaxy is consistent with a cosecant law such as could be used to describe extinction in the solar neighborhood. The SN II-L's seem to be more strongly associated with giant H II regions than Type II SNs with a plateau (SN II-P's), and the majority of SN II-L's are probably massive stars. It is suggested that mass loss in SN II-L's progenitors might lead to SN Ib's. There are a few significantly higher luminosity SN II-L's, but after allowance for the volume selection effect, these are only 4%-8% of SN II-L's.