A study of the low-luminosity Type II-Plateau supernova 2008bk

TL;DR

This study models the low-luminosity Type II-Plateau supernova 2008bk using a low-mass red supergiant progenitor, successfully reproducing its light curves and spectra, and explores how progenitor properties influence supernova features.

Contribution

The paper presents a detailed explosion model of SN 2008bk with a low-mass progenitor and analyzes the effects of progenitor radius, mass, and chemical mixing on supernova observables.

Findings

Model reproduces SN 2008bk light curves and spectra satisfactorily.

Progenitor radius increase raises luminosity and plateau brightness.

Ejecta mass increase extends the plateau duration.

Abstract

Supernova (SN) 2008bk is a well observed low-luminosity Type II event visually associated with a low-mass red-supergiant progenitor. To model SN 2008bk, we evolve a 12Msun star from the main sequence until core collapse, when it has a total mass of 9.88Msun, a He-core mass of 3.22Msun, and a radius of 502Rsun. We then artificially trigger an explosion that produces 8.29Msun of ejecta with a total energy of 2.5x10^50erg and ~0.009Msun of 56Ni. We model the subsequent evolution of the ejecta with non-Local-Thermodynamic-Equilibrium time-dependent radiative transfer. Although somewhat too luminous and energetic, this model reproduces satisfactorily the multi-band light curves and multi-epoch spectra of SN 2008bk, confirming the suitability of a low-mass massive star progenitor. As in other low-luminosity SNe II, the structured Halpha profile at the end of the plateau phase is probably caused by BaII 6496.9A rather than asphericity. We discuss the sensitivity of our results to changes in progenitor radius and mass, as well as chemical mixing. A 15% increase in progenitor radius causes a 15% increase in luminosity and a 0.2mag V-band brightening of the plateau but leaves its length unaffected. An increase in ejecta mass by 10% lengthens the plateau by ~10d. Chemical mixing introduces slight changes to the bolometric light curve, limited to the end of the plateau, but has a large impact on colours and spectra at nebular times.