FAR-INFRARED WATER LINE EMISSIONS FROM CIRCUMSTELLAR OUTFLOWS

We have modeled the far-infrared water line emission expected from cir cumstellar outflows from oxygen-rich late-type stars, as a function of the mass-loss rate and the terminal outflow velocity. For each mass-l oss rate and terminal outflow velocity considered, we computed self-co nsistently the gas density, temperature, outflow velocity, and water a bundance as a function of distance from the star. We then used an esca pe probability method to solve for the equilibrium level populations o f 80 rotational states of water and thereby obtained predictions for t he luminosity of a large number of far-infrared rotational transitions of water. In common with previous models, our model predicts that wat er will be copiously produced in the warm circumstellar gas and that w ater rotational emission will dominate the radiative cooling. However, our use of a realistic radiative cooling function for water leads to a lower gas temperature than that predicted in previous models. Our pr edictions for the far-infrared water line luminosities are consequentl y significantly smaller than those obtained in previous studies. Obser vations to be carried out by the Infrared Space Observatory will provi de a crucial test of the models presented here.