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

Abstract

Context. Vibrationally excited emission from the SiO and H2O molecules probes the innermost circumstellar envelopes of oxygenrich 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 v2 = 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. © ESO 2006.