SNIa Diversity: Theory and Diagnostics

Abstract

Existing evidence of photometric and spectroscopic diversity among Type la supernovae is compared with the predictions from physical modeling of the explosions. Concerning light curves, changes in the central ignition density of massive (M ~ Mch) C+O white dwarfs alone do not give appreciable variation. Spectroscopic diversity has been found in the nebular phase, the underluminous SN 1991bg providing an extreme case. A range of 0.4-0.8 MQ of 56 Ni synthesized in the explosions is derived from the nebular spectra of a sample of SNe la. For SN 1991bg, however, a 56 Ni mass of ~ 0.1 M© only is obtained. That leads us to explore models based on the detonation of low-mass WDs for this SN. Additionally, a nebular spectrum of SN 1991bg shows narrow Ha emission at the position of the SN. If this emission is confirmed against background contamination from the galaxy, it would be first evidence of a nondegenerate, H-rich companion in a SNIa.