Program: GN-2008A-Q-17

We propose to obtain nebular-phase spectra of several well-observed Type I supernovae (SNe). Without the complications of a hydrogen envelope, modeling of these spectra reveals many basic properties of the explosion mechanism, shedding light on both core-collapse events and thermonuclear SNe. Sophisticated models allow us to derive the mass and distribution of radioactive 56Ni, the composition and distribution of other elements, and the kinetic energy released by the explosion. For Type Ia SNe (thermonuclear) in particular, the modeling of the nebular-phase spectra shows properties that correlate well with light-curve shape, and thus luminosity. The spectra of SNe in the nebular phase provide a direct probe of the physics of the explosion itself, unhindered by the outer layers of the progenitor. These spectra can reveal the actual nature of the SN explosion that is not necessarily apparent in the photospheric phase.