Red supergiants as potential Type IIn supernova progenitors: Spatially resolved 4.6 micron CO emission around VY CMa and Betelgeuse

TL;DR

This study uses high-resolution 4.6 micron CO spectra to analyze the circumstellar environments of Betelgeuse and VY CMa, revealing their potential as Type IIn supernova progenitors based on their mass-loss histories.

Contribution

It provides detailed spatially resolved CO emission data around two RSGs, highlighting differences in their circumstellar structures and implications for supernova progenitor models.

Findings

VY CMa's circumstellar environment shows asymmetric clumpy CO emission.

Betelgeuse's CO shell is smaller and more spherical than its KI shell.

VY CMa could produce a Type IIn supernova if it explodes now.

Abstract

We present high-resolution 4.6micron CO spectra of the circumstellar environments of two RSGs that are potential SN progenitors: Betelgeuse and VY CMa. Around Betelgeuse, 12CO emission within 3arcsec follows a mildly clumpy but otherwise spherical shell, smaller than its 55arcsec shell in KI lambda7699. In stark contrast, 4.6micron CO emission around VY CMa is coincident with bright KI in its clumpy asymmetric reflection nebula, within 5arcsec of the star. Our CO data reveal redshifted features not seen in KI spectra of VY CMa, indicating a more isotropic distribution of gas punctuated by randomly distributed asymmetric clumps. The relative CO and KI distribution in Betelgeuse arises from ionization effects within a steady wind, whereas in VY CMa, KI is emitted from skins of CO cloudlets resulting from episodic mass ejections 500--1000 yr ago. In both cases, CO and KI trace potential pre-SN circumstellar matter: we conclude that an extreme RSG like VY CMa might produce a Type IIn event like SN1988Z if it were to explode in its current state, but Betelgeuse will not. VY CMa demonstrates that LBVs are not necessarily the only progenitors of SNe IIn, but it underscores the requirement that SNe IIn suffer enhanced episodic mass loss shortly before exploding.