321 GHz submillimeter water masers around evolved stars

Abstract

The 321 GHz 10(29) - 9(36) transition of water vapor has been detected toward 10 Mira and semiregular variables and one supergiant. Maser action is almost certainly involved in all the cases, since the observed spectra generally show a few narrow components which have quite high intensities in some cases. Spectra of the 22 GHz 6(16) - 5(23) transition of H2O were taken almost simultaneously with the 321 GHz spectra. The 22 GHz emission feature are observed at velocities that do not show detectable 321 GHz emission, and vice versa. The ratio between the integrated lunminosities observed in the 22 and 321 GHz line is comparable to or less than unity for most stars. Toward VY CMa, the velocity spread of the 321 GHz line is much smaller than that of the 22 GHz line, but the strongest emission in both lines is at similar velocities.