2006A&A...454L.107M

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. Observations were made to search for rotational lines in the lowest vibrationally excited state of H₂O. The APEX telescope was used for observations of H₂O lines at frequencies around 300GHz. 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 ν₂=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.