The Physics of Type Ia Supernova Light Curves. II. Opacity and Diffusion

We examine the nature of the opacity and radiation transport in Type Ia supernova. The dominant opacity arises from line transitions. We discuss the nature of line opacities and diffusion in expanding media and the appropriateness of various mean and expansion opacities used in light curve calculations. Fluorescence is shown to to be the dominant physical process governing the rate at which energy escapes the supernova. A sample lightcurve is presented obtained by a time-dependent solution of the radiative transport equation with a spectral resolution of 80 km s<sup.-1 and employing an LTE equation of state. The result compares favorably with lightcurves and spectra of typical supernova and is used to illustrate the physics controlling the evolution of the lightcurve and especially the secondary maxima see in infrared photom