CIRCUMSTELLAR CO EMISSION OF EVOLVED STARS AND MASS-LOSS

We have calculated the CO J = 1 --> 0 and 2 --> 1 emission of circumstellar molecular envelopes, allowing the physical parameters, namely, the mass-loss rate, the CO abundance, the distance to the envelope, and the parameter specifying the amount of gas-dust collisional heating, to take on values over wide ranges. From these results we establish two relations between the intensity and shape of the J = 1 --> 0 or 2 --> 1 line and the above-mentioned variables. We have also examined the effects of CO dissociation by the interstellar UV field, the presence of an appreciable velocity gradient in the gas flow, and the 4.6 mum continuum flux level. We apply the two relations to the circumstellar envelopes IRC + 10216, chi Cyg, and U Cam.