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Cool, evolved stars have copious, enriched winds. The structure of thesewinds and the way they are accelerated is not well known. We need to improveour understanding by studying the dynamics from the pulsating stellar surfaceto about 10 stellar radii, where radiation pressure on dust is fully effective.Some red supergiants have highly asymmetric nebulae, implicating additionalforces. We retrieved ALMA Science Verification data providing images of sub-mmline and continuum emission from VY CMa. This enables us to locate water maserswith milli-arcsec precision and resolve the dusty continuum. The 658-, 321- and325-GHz masers lie in irregular, thick shells at increasing distances from thecentre of expansion. For the first time this is confirmed as the stellarposition, coinciding with a compact peak offset to the NW of the brightestcontinuum emission. The maser shells (and dust formation zone) overlap butavoid each other on tens-au scales. Their distribution is broadly consistentwith excitation models but the conditions and kinematics appear to becomplicated by wind collisions, clumping and asymmetries.

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