Determining the main-sequence mass of Type II supernova progenitors

TL;DR

This study uses radiation-hydrodynamics simulations to link supernova ejecta velocities and nebular spectral features to progenitor main-sequence mass, suggesting most Type II-P supernovae originate from stars less than 20 solar masses.

Contribution

It introduces a method to estimate progenitor main-sequence mass from supernova spectra, connecting explosion energy, ejecta velocities, and spectral line widths.

Findings

Photospheric velocity at 15 days indicates explosion energy.

Nebular spectra suggest progenitors are typically under 20 solar masses.

Narrow nebular lines do not support high-mass progenitors in 25-30 solar masses.

Abstract

We present radiation-hydrodynamics simulations of core-collapse supernova (SN) explosions, artificially generated by driving a piston at the base of the envelope of a rotating or non-rotating red-supergiant progenitor star. We search for trends in ejecta kinematics in the resulting Type II-Plateau (II-P) SN, exploring dependencies with explosion energy and pre-SN stellar-evolution model. We recover the trivial result that larger explosion energies yield larger ejecta velocities in a given progenitor. However, we emphasise that for a given explosion energy, the increasing helium-core mass with main-sequence mass of such Type II-P SN progenitors leads to ejection of core-embedded oxygen-rich material at larger velocities. We find that the photospheric velocity at 15d after shock breakout is a good and simple indicator of the explosion energy in our selected set of pre-SN models. This measurement, combined with the width of the nebular-phase OI6303-6363A line, can be used to place an upper-limit on the progenitor main-sequence mass. Using the results from our simulations, we find that the current, but remarkably scant, late-time spectra of Type II-P SNe support progenitor main-sequence masses inferior to ~20Msun and thus, corroborate the inferences based on the direct, but difficult, progenitor identification in pre-explosion images. The narrow width of OI6303-6363A in Type II-P SNe with nebular spectra does not support high-mass progenitors in the range 25-30Msun. Combined with quantitative spectroscopic modelling, such diagnostics offer a means to constrain the main-sequence mass of the progenitor, the mass fraction of the core ejected, and thus, the mass of the compact remnant formed.