Light curves and Hα luminosities as indicators of 56Ni mass in type IIP supernovae

The possibility is investigated that the Halpha luminosity at the nebular epoch may be an additional indicator of Ni-56 mass in type II supernovae with plateau (SNe IIP), on the basis of available photometry and spectra. We first derive the Ni-56 mass from the M-V magnitude on the radioactive tail using a standard approach. A confirmation of the correlation between Ni-56 mass and plateau M-V 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 Ni-56 mass. If confirmed, this relation may provide distance and extinction independent estimates of the amount of Ni-56 in SNe IIP. We then apply upgraded radioactive models of Halpha luminosity at the nebular epoch and claim that it may be a good indicator of Ni-56, if mass, energy and mixing properties vary moderately (within factor similar to1.4) among SNe IIP. This method of the Ni-56 mass determination from Halpha luminosities yields results which are consistent with the photometric mass of Ni-56 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.