Arcsecond resolution mapping of Sulfur Dioxide emission in the circumstellar envelope of VY Canis Majoris

TL;DR

This study uses high-resolution submillimeter observations to map SO2 emission around VY CMa, revealing distinct outflow regions, a spherical wind, and chemical abundance patterns that inform models of circumstellar chemistry.

Contribution

First high-resolution mapping of SO2 in VY CMa's envelope, showing spatial distribution and chemical abundance ratios that support shock-related chemical models.

Findings

SO2 emission in three outflows and a spherical wind

SO2 abundance exceeds that of SO beyond certain radii

SO2 distribution is fragmented and consistent with shock models

Abstract

We report Submillimeter Array observations of SO2 emission in the circumstellar envelope of the red supergiant VY CMa, with an angular resolution of ~1". SO2 emission appears in three distinct outflow regions surrounding the central continuum peak emission that is spatially unresolved. No bipolar structure is noted in the sources. A fourth source of SO2 is identified as a spherical wind centered at the systemic velocity. We estimate the SO2 column density and rotational temperature assuming local thermal equilibrium (LTE) as well as perform non-LTE radiative transfer analysis using RADEX. Column densities of SO2 are found to be ~10^16 cm^-2 in the outflows and in the spherical wind. Comparison with existing maps of the two parent species OH and SO shows the SO2 distribution to be consistent with that of OH. The abundance ratio f_SO2/f_SO is greater than unity for all radii greater than at least 3x10^16 cm. SO2 is distributed in fragmented clumps compared to SO, PN, and SiS molecules. These observations lend support to specific models of circumstellar chemistry that predict f_SO2/f_SO>1 and may suggest the role of localized effects such as shocks in the production of SO2 in the circumstellar envelope.