2015A&A...573L...1O

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 129mas at 321GHz and 59mas at 658GHz, thus allowing us to trace dust on spatial scales down to 11R_* (71AU). Two prominent dust components are detected and resolved. The brightest dust component, C, is located 334mas (61R_*) southeast of the star and has a dust mass of at least 2.5x10^–4M_☉. It has a dust emissivity spectral index of β=-0.1 at its peak, implying that it is optically thick at these frequencies with a cool core of T_d≲100K. 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 4.0x10^–5M_☉. It also contains a weaker dust feature extending over 60R_* to the north with the total component having a typical dust emissivity spectral index of β=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 5x10^–6M_☉/yr. 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.