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Astron. Astrophys. 344, 687-695 (1999)

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4. Conclusions

We have used MC93's bow shock driven shell model of a protostellar outflow combined with molecular cooling rates to predict temperature as a function of length along the molecular outflow. We have compared the results of modelling with observations of the L483 outflow, where we have carried out a multitransition study of CO in order to measure the gas temperature for comparison with the predictions.

In a simple bow shock model, the expanding shell sweeps up the ambient medium, conserving momentum but losing kinetic energy which is available to heat the gas in the shell. By modelling this process we find that the temperature rises with distance from the star towards the head of the driving jet, rising more strongly if there is a falling density gradient away from the star. Comparing the gain in thermal energy with molecular cooling functions, the heating is sufficient to maintain the outflow at temperatures several times hotter than the ambient interstellar cloud for most of its length. For our example model, for which we have chosen parameters typical of young outflows such as L483, the temperature remains over 50 K for at least half the length of the outflow (more if the density gradient is less steep than [FORMULA]).

The results of an excitation study of CO in L483 (including transitions up to [FORMULA]) are consistent with the temperatures and gradients predicted by the shell model, provided the optical depth remains high along the length of the outflow and the ambient density is fairly flat.

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© European Southern Observatory (ESO) 1999

Online publication: March 18, 1999
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