ALMA Reveals VY CMa's Sub-mm H2O Maser and Dust Distribution

Paper in proceeding, 2015

Cool, evolved stars have copious, enriched winds but observation constrains do not yet fully constrain models for need the dynamics of mass loss from the pulsating stellar surface to 10 stellar radii, where radiation pressure on dust is fully effective. 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. Their distribution is broadly consistent with excitation models but the conditions and kinematics are complicated by wind collisions, clumping and asymmetries.