ARCSECOND RESOLUTION MAPPING OF SULFUR DIOXIDE EMISSION IN THE CIRCUMSTELLAR ENVELOPE OF VY CANIS MAJORIS

Abstract

We report Submillimeter Array observations of SO[subscript 2] emission in the circumstellar envelope (CSE) of the red supergiant VY Canis Majoris, with an angular resolution of ≈1''. SO[subscript 2] 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 SO[subscript 2] is identified as a spherical wind centered at the systemic velocity. We estimate the SO[subscript 2] column density and rotational temperature assuming local thermal equilibrium (LTE) as well as perform non-LTE radiative transfer analysis using RADEX. Column densities of SO[subscript 2] are found to be ~10[superscript 16] cm[superscript –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 [fSO[subscript 2] over fSO] is greater than unity for all radii larger than 3 × 10[superscript 16] cm. SO[subscript 2] is distributed in fragmented clumps compared to SO, PN, and SiS molecules. These observations lend support to specific models of circumstellar chemistry that predict [fSO[subscript 2] over fSO] > 1 and may suggest the role of localized effects such as shocks in the production of SO2 in the CSE.