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

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.

Letter 4 pages, 5 figures plus appendix with 3 figures. Accepted by Astronomy and Astrophysics Letters

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• ALMA Observations of Anisotropic Dust Mass-loss in the Inner Circumstellar Environment of the Red Supergiant VY Canis Majoris
• On massive dust clumps in the envelope of the red supergiant VY Canis Majoris
• ATOMIUM: Probing the inner wind of evolved O-rich stars with new, highly excited H${}_2$O and OH lines
• Water maser variability in a high-mass YSO outburst -- VERA and ALMA observations of S255 NIRS 3
• Vibrationally excited water emission at 658 GHz from evolved stars
• History of two mass loss processes in VY CMa. Fast outflows carving older ejecta
• Model of the vibrationally excited H${}_2$O maser at 658 GHz in circumstellar envelopes around asymptotic giant branch stars
• The Science Case for Simultaneous mm-Wavelength Receivers in Radio Astronomy
• Submillimetre water masers at 437, 439, 471, and 474 GHz towards evolved stars. APEX observations and radiative transfer modelling
• Molecules and Chemistry in Red Supergiants
• Red Supergiants in the Milky Way and Nearby Galaxies