Explosion Diagnostics of Type Ia Supernovae from Early Infrared Spectra

Models of infrared spectra of Type Ia supernovae around maximum light are presented. The underlying dynamic models are delayed detonation explosions in Chandrasekhar mass carbon/oxygen white dwarfs. In combination with the radiative transport codes employed here, these models provide plausible fits to the optical spectra of "normal" Type Ia supernovae. Two independent radiative transport codes are used, one that assumes LTE and one that computes non-LTE excitations and ionization. The models are compared with the infrared data available in the literature. The independent codes give a reasonable representation of the data and provide physical explanations for their origin independent of the detailed assumptions of the radiative transfer. The infrared gives an especially powerful diagnostic of the dynamic model because it probes different depths at the same epoch within the exploded white dwarf with strongly variable line-blanketing opacity. The velocity of the transition zone between explosive oxygen and carbon burning can be directly determined. The velocity at which the burning to nickel stops can also be probed. These velocities are very sensitive to the explosion physics.