Letter to the Editor

Submillimeter vibrationally excited water emission from the peculiar red supergiant VY Canis Majoris

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: [kmenten;sphilipp;rguesten]@mpifr-bonn.mpg.de
² Observatorio Astronomico Nacional, C/Alfonso XII, No. 3, 28014 Madrid, Spain e-mail: j.alcolea@oan.es
³ Space Science and Technology Department Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK e-mail: E.T.Polehampton@rl.ac.uk
⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA e-mail: sbruenken@cfa.harvard.edu

Received: 19 April 2006
Accepted: 23 May 2006

Abstract

Context.Vibrationally excited emission from the SiO and H₂O molecules probes the innermost circumstellar envelopes of oxygen-rich red giant and supergiant stars. VY CMa is the most prolific known emission source in these molecules.

Aims.Observations were made to search for rotational lines in the lowest vibrationally excited state of H₂O.

Methods.The APEX telescope was used for observations of H₂O lines at frequencies around 300 GHz.

Results.Two vibrationally excited H₂O lines were detected, a third one could not be found. In one of the lines we find evidence for weak maser action, similar to known (sub)millimeter  = 1 lines. We find that the other line's intensity is consistent with thermal excitation by the circumstellar infrared radiation field. Several SiO lines were detected together with the H₂O lines.