MOLECULAR ROTATIONAL LINE-PROFILES FROM OXYGEN-RICH RED GIANT WINDS

We have developed a radiative transfer model of the dust and gas envel opes around late-type stars. The gas kinetic temperature for each star is calculated by solving equations of motion and the energy balance s imultaneously. The main processes include viscous heating and adiabati c and radiative cooling. Heating is dominated by viscosity as the grai ns stream outward through the gas, with some contribution in oxygen-ri ch stars by near-IR pumping of H2O followed by collisional de-excitati on in the inner envelope. For O-rich stars, rotational H2O cooling is a dominant mechanism in the middle part of the envelope, with CO cooli ng being less significant. We have applied our model to three well-stu died oxygen-rich red giant stars. The three stars cover a wide range o f mass-loss rates, and hence they have different temperature structure s. The derived temperature structures are used in calculating CO line profiles for these objects. Comparison of the dust and gas mass-loss r ates suggests that mass-loss rates are not constant during the asympto tic giant branch phase. In particular, the results show that the low C O 1-0 antenna temperatures of OH/IR stars reflect an earlier phase of much lower mass-loss rate.