Type II-Plateau supernova radiation: Dependences on progenitor and explosion properties

Abstract

We explore the properties of Type II-Plateau (II-P) supernovae (SNe) together with their red supergiant (RSG) star progenitors. Using MESA STAR, we modulate the parameters (e.g. mixing length, overshoot, rotation, metallicity) that control the evolution of a 15Mȯ mainsequence star to produce a variety of physical pre-SN models and SN II-P ejecta. We extend previous modelling of SN II-P radiation to include photospheric and nebular phases, as well as multiband light curves and spectra. Our treatment does not assume local thermodynamic equilibrium, is time dependent, treats explicitly the effects of line blanketing and incorporates non-thermal processes. We find that the colour properties of SNe II-P require large model atoms for Fe I and Fe II, much larger than previously adopted. The colour properties also imply RSG progenitors of limited extent (~500 Rȯ) -larger progenitor stars produce an SN II-P radiation that remains too blue for too long. This finding calls for a reduction of RSG radii, perhaps through a strengthening of convective energy transport in RSG envelopes. Increased overshoot and rotation reduce the ratio of ejecta to helium-core mass, similarly to an increase in main-sequence mass, and thus complicate the inference of progenitor masses. In contrast to the great sensitivity on progenitor radius, SN II-P colour evolution appears insensitive to variations in explosion energy. Finally, we document the numerous SN II-P signatures that vary with progenitor metallicity, revealing their potential for metallicity determinations in the nearby and distant Universe.