H 2O Emission from Evolved Stars at the Far-Infrared and Submillimeter Wavelengths

Intensities of far-infrared and submillimeter transitions of H2O in circumstellar envelopes of evolved stars are calculated. The radiative excitation of nu(2) and nu(3) vibrational states is taken into account. For a thick circumstellar envelope with a mass-loss rate of 0.00001 solar masses/yr, several of the strongest lines, such as the 2(12)-1(01) transition at 179.5 microns, have enough flux to be observed by the spectrometers of the Infrared Space Observatory. For the stars with lower mass-loss rate (3 x 10 to the -7th solar masses/yr), it is possible to detect a line from the sources within a distance of 300 pc with a modest integration time.