ALMA sub-mm maser and dust distribution of VY Canis Majoris

TL;DR

This study uses ALMA data to map the distribution of masers and dust around VY Canis Majoris, revealing complex wind structures, asymmetries, and the spatial relationship between maser shells and dust formation zones.

Contribution

First high-resolution imaging of sub-mm masers and dust in VY Canis Majoris, showing their irregular distribution and interaction, advancing understanding of stellar wind dynamics.

Findings

Maser shells are irregular and at increasing distances from the star.

Maser and dust zones overlap but avoid each other on small scales.

Wind structures are complex due to collisions, clumping, and asymmetries.

Abstract

Cool, evolved stars have copious, enriched winds. The structure of these winds and the way they are accelerated is not well known. We need to improve our understanding by studying the dynamics from the pulsating stellar surface to about 10 stellar radii, where radiation pressure on dust is fully effective. Some red supergiants have highly asymmetric nebulae, implicating additional forces. We retrieved ALMA Science Verification data providing images of sub-mm line and continuum emission from VY CMa. This enables us to locate water masers with milli-arcsec precision and resolve the dusty continuum. The 658-, 321- and 325-GHz masers lie in irregular, thick shells at increasing distances from the centre of expansion. For the first time this is confirmed as the stellar position, coinciding with a compact peak offset to the NW of the brightest continuum emission. The maser shells (and dust formation zone) overlap but avoid each other on tens-au scales. Their distribution is broadly consistent with excitation models but the conditions and kinematics appear to be complicated by wind collisions, clumping and asymmetries.