Abstract
The possibility is investigated that the Hα luminosity at the nebular epoch may be an additional indicator of 56Ni mass in type II supernovae with plateau (SNe IIP), on the basis of available photometry and spectra. We first derive the 56Ni mass from the MV magnitude on the radioactive tail using a standard approach. A confirmation of the correlation between 56Ni mass and plateau MV magnitude found recently by Hamuy (2003) is evident. There is strong evidence of a correlation between steepness of the V light curve slope at the inflection time and the 56Ni mass. If confirmed, this relation may provide distance and extinction independent estimates of the amount of 56Ni in SNe IIP. We then apply upgraded radioactive models of Hα luminosity at the nebular epoch and claim that it may be a good indicator of 56Ni, if mass, energy and mixing properties vary moderately (within factor ~1.4) among SNe IIP. This method of the 56Ni mass determination from Hα luminosities yields results which are consistent with the photometric mass of 56Ni mass to within 20%. This result also implies that the parameters of SNe IIP events (mass, energy and mixing properties) are rather similar among the majority of SNe IIP, except for rare cases of SN II intermediate between IIP and IIL (linear), of which SN 1970G is an example.