THERMAL H2O EMISSION FROM THE HERBIG-HARO FLOW HH-54

The first detection of thermal water emission from a Herbig-Haro objec t is presented. The observations were performed with the LWS (Long Wav elength Spectrograph) aboard Iso (Infrared Space Observatory). Besides H2O, rotational lines of CO are present in the spectrum of HH 54. The se high-J CO lines are used to derive the physical model parameters of the FIR (far-infrared) molecular line emitting regions. This model fi ts simultaneously the observed OH and H2O spectra for an OH abundance X(OH) = 10(-6) and a water vapour abundance X(H2O) = 10(-5). At a dist ance of 250 pc, the total CO, OH and H2O rotational line cooling rate is estimated to be 1.3 10(-2) L., which is comparable to the mechanica l luminosity generated by the 10 km s(-1) shocks, suggesting that prac tically all of the cooling of the weak-shock regions is done by these three molecular species alone.