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

¹ JBCA, School of Physics and Astronomy, Univ. of Manchester, UK
e-mail: amsr@jb.man.ac.uk
² NRAO, 520 Edgemont Road, Charlottesville, VA22903, USA
³ ESO Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
⁴ Joint ALMA Observatory/European Southern Observatory, 3107 Alonso de Cordova, Vitacura, Santiago, Chile
⁵ Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
⁶ Univ. Bordeaux, LAB, UMR 5804, 33270 Floirac, France
⁷ CNRS, LAB, UMR 5804, 33270 Floirac, France
⁸ Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁹ Hamburger Sternwarte, Univ. of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Hamburg, Germany
¹⁰ School of Physics, Trinity College Dublin, 2, Dublin, Ireland
¹¹ LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, PSL, 5 place Jules Janssen, 92195 Meudon, France
¹² UMI-FCA, CNRS/INSU (UMI 3386), France
¹³ Dept. de Astronomía, Universidad de Chile, Casilla 36-D Santiago, Chile
¹⁴ Dept. of Astrophysics, Univ. of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria
¹⁵ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 66x, Cambridge, MA 02138, USA
¹⁶ Dept. of Physics & Astronomy, Johns Hopkins Univ., 3400 North Charles Street, Baltimore, MD 21218, USA
¹⁷ Ural Federal University, Ekaterinburg, Russia
¹⁸ NAOJ, 2-21-1 Osawa, Mitaka, 181-8588 Tokyo, Japan
¹⁹ IAASARS, National Observatory of Athens, 15236 Athens, Greece
²⁰ Dept. of Physics and Astronomy, University College London, WC1E 6BT, UK

Received: 18 September 2014
Accepted: 16 October 2014

Abstract

Aims. Cool, evolved stars have copious, enriched winds. Observations have so far not fully constrained models for the shaping and acceleration of these winds. We need to understand the dynamics better, from the pulsating stellar surface to ~10 stellar radii, where radiation pressure on dust is fully effective. Asymmetric nebulae around some red supergiants imply the action of additional forces.

Methods. 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 accuracy and to resolve the dusty continuum.

Results. 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 overlap but avoid each other on scales of up to 10 au. Their distribution is broadly consistent with excitation models but the conditions and kinematics are complicated by wind collisions, clumping, and asymmetries.