A radioactive excitation source model for the late time spectra of Type I supernovae

Abstract

The radioactive excitation source model of Meyerott (1978) is used to interpret the similarity of the spectra of SN 1972e in NGC 5253 taken 245 days after maximum and the synthetic spectra of F(+) and F(++) calculated as a function of electron temperature assuming a Boltzmann population of the metastable levels of F(+) and F(++). The model predicts that a mass of about 0.5 solar mass is required to produce the observed 4:1 ratio of Fe(++) to Fe(+). About the same mass of explosively synthesized Ni is required to produce the excitation source. This is consistent with an interpretation that the supernova envelope at late times consists mostly of Fe.