1999A&A...344..687H

The acceleration mechanism for protostellar outflows is still uncertain, despite many dynamical studies. Active acceleration processes are expected to heat the molecular gas, and it should be possible to choose between the possible outflow models by excitation studies which measure the temperature of the molecular gas. We show how temperature predictions can be made from a simple bow-shock driven shell model and compared with temperature estimates from excitation studies. As the momentum-conserving shell expands the kinetic energy lost is sufficient to heat the molecular gas to temperatures many times that of the ambient cloud. The energy transfer - and therefore the temperature - is greatest near to the bow shock and therefore the temperature rises with distance from the star. We present a multitransition CO study of the young outflow L483 and compare temperature predictions from the shell model with measurements of the CO excitation.