Explosions of pulsating red supergiants: a natural pathway for the diversity of Type II-P/L supernovae

TL;DR

This paper models pulsations in red supergiants and shows how their phases at explosion influence supernova light curves, potentially explaining the observed diversity in Type II-P/L supernovae.

Contribution

It provides a self-consistent hydrodynamical model of RSG pulsations and links these pulsations to variations in supernova light curves, a novel approach compared to static progenitor models.

Findings

Pulsations are driven by the $ ext{-} ext{-}$-mechanism.

SN light curves vary with pulsation phase, showing flat or declining profiles.

Pulsations can cause envelope ejections and increase SN diversity.

Abstract

Red supergiants (RSGs), which are progenitors of hydrogen-rich Type II supernovae (SNe), have been known to pulsate from both observations and theory. The pulsations can be present at core collapse and affect the resulting SN. However, SN light curve models of such RSGs commonly use hydrostatic progenitor models and ignore pulsations. Here, we model the final stages of a 15 solar-mass RSG and self-consistently follow the hydrodynamical evolution. We find the growth of large amplitude radial pulsations in the envelope. After a transient phase where the envelope restructures, the pulsations settle to a steady and periodic oscillation with a period of 817 days. We show that they are driven by the $\kappa\gamma$-mechanism, which is an interplay between changing opacities and the release of recombination energy of hydrogen and helium. This leads to complex and non-coherent expansion and contraction in different parts of the envelope, which greatly affect the SN progenitor properties, including its location in the Hertzsprung-Russell diagram. We simulate SN explosions of this model at different pulsations phases. Explosions in the compressed state result in a flat light curve (Type II-P). In contrast, the SN light curve in the expanded state declines rapidly, reminiscent of a Type II-L SN. For cases in between, we find light curves with various decline rates. Features in the SN light curves are directly connected to features in the density profiles. These are in turn linked to the envelope ionization structure, which is the driving mechanism of the pulsations. We predict that some of the observed diversity in Type II SN light curves can be explained by RSG pulsations. For more massive RSGs, we expect stronger pulsations that might even lead to dynamical mass ejections of the envelope and to an increased diversity in SN light curves.