Molecular hydrogen emission associated with high velocity flows. A tracer for low velocity shocks

The production of supersonic bipolar stellar winds by pre-main sequence stars was studied by observing H2 emission in the HH7-11 complex. Results show that H2 emission is clumped on a similar scale to that observed in visible emission, but that H2 and visible emission are not always coincident. In at least one case diffuse extended H2 emission is observed, possibly associated with the outflow. The H2 emission associated with HH 7, an extremely low excitation HH object, is coincident with the visible emission. This strongly implies that both emissions arise from a single cloudlet shock. Models used to predict visible emission line strengths do not include H2 emission in the cooling of such shocks. This may explain the anomalies in line strengths observed in HH 7.