ALMA Observations of Anisotropic Dust Mass-loss in the Inner Circumstellar Environment of the Red Supergiant VY Canis Majoris

Abstract

The processes leading to dust formation and the subsequent role it plays in driving mass loss in cool evolved stars is an area of intense study. Here we present high resolution ALMA Science Verification data of the continuum emission around the highly evolved oxygen-rich red supergiant VY CMa. These data enable us to study the dust in its inner circumstellar environment at a spatial resolution of 129 mas at 321 GHz and 59 mas at 658 GHz, thus allowing us to trace dust on spatial scales down to 11 R${}_{\star }$ (71 AU). Two prominent dust components are detected and resolved. The brightest dust component, C, is located 334 mas (61 R${}_{\star }$) South East of the star and has a dust mass of at least $2.5\times 10^{-4}$ M${}_{\odot }$. It has a dust emissivity spectral index of $\beta =-0.1$ at its peak, implying that it is optically thick at these frequencies with a cool core of $T_d\lesssim 100$ K. Interestingly, not a single molecule in the ALMA data has emission close to the peak of this massive dust clump. The other main dust component, VY, is located at the position of the star and contains a total dust mass of $4.0\times 10^{-5}$M${}_{\odot }$. It also contains a weaker dust feature extending over $60$ R${}_{\star }$ to the North with the total component having a typical dust emissivity spectral index of $\beta =0.7$. We find that at least $17\%$ of the dust mass around VY CMa is located in clumps ejected within a more quiescent roughly spherical stellar wind, with a quiescent dust mass loss rate of $5\times 10^{-6}$ M${}_{\odot }$yr${}^{-1}$. The anisotropic morphology of the dust indicates a continuous, directed mass loss over a few decades, suggesting that this mass loss cannot be driven by large convection cells alone.

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• Large dust grains in the wind of VY Canis Majoris
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• The Mass-Loss History of the Red Hypergiant VY CMa
• 3D MHD astrospheres: applications to IRC-10414 and Betelgeuse
• The Unexpected Spectrum of the Innermost Ejecta of the Red Hypergiant VY CMa
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• Imaging the innermost circumstellar environment of the red supergiant WOH G64 in the Large Magellanic Cloud
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• ALMA Compact Array observations of the Fried Egg nebula: Evidence for large-scale asymmetric mass-loss from the yellow hypergiant IRAS 17163-3907
• ALMA Band-to-band Phase Referencing: Imaging Capabilities on Long Baselines and High Frequencies
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