Far-Infrared Water Line Emissions from Circumstellar Outflows

We have modeled the far-infrared water line emission expected fromcircumstellar outflows from oxygen-rich late-type stars, as a function of themass-loss rate and the terminal outflow velocity. For each mass-loss rate andterminal outflow velocity considered, we computed self-consistently the gasdensity, temperature, outflow velocity, and water abundance as a function ofdistance from the star. We then used an escape probability method to solve forthe equilibrium level populations of 80 rotational states of water and therebyobtained predictions for the luminosity of a large number of far-infraredrotational transitions of water. In common with previous models, our modelpredicts that water will be copiously produced in the warm circumstellar gas,and that water rotational emission will dominate the radiative cooling.However, our use of a realistic radiative cooling function for water leads to alower gas temperature than that predicted in previous models. Our predictionsfor the far-infrared water line luminosities are consequently significantlysmaller than those obtained in previous studies. Observations to be carried outby the Infrared Space Observatory will provide a crucial test of the modelspresented here.Comment: 10 page LaTeX file of manuscript using AASTeX macro package and 4 Postscript figures, tarred, gziped and uuencoded. To appear in ApJ Letters (tentative publication date: Nov. 10, 1995