Spectra of Supernovae During the Photospheric Phase

Abstract

Photospheric-phase spectra have a central role in the classification and study of supernovae of all types. We describe the basic physical picture that can be used to understand photospheric-phase spectra and comment on some of the complications and subtleties associated with studying photospheres in super-novae. We discuss the main radiation processes that contribute to the opacity and emissivity in supernova ejecta of both Type I and Type II events and describe how the relative roles of these processes vary across the ultraviolet to near-infrared spectral regions. We present a simple theoretical framework that can be used to understand the shaping of spectral features in supernovae, in particular the standard P Cygni line profile shape, which often appears in the analysis of supernova spectra. Although we focus on qualitative understanding, we comment on some of the challenges involved in quantitative modelling and discuss common approximations that have been used in supernova spectral synthesis. We conclude with a short overview of applications of spectral modelling and comment on the wide range of approaches that has been used.