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Proper Motions and Variability of the H$_2$ Emission in the HH~46/47system

We report here on the first proper motion measurements of molecular hydrogen emission features in the Herbig-Haro 46/47 outflow. Assuming a distance of 350 pc to this flow, the inferred tangential velocities range from a few tens to almost 500 km/s . The highest velocities are observed for H2 knots either in, or close to, the jet/counterjet axes. Knots constituting the wings of the large scale H2 bow (see, for example, Eislöffel et al. 1994) are found to move much more slowly. These results appear to be in agreement with recent numerical simulations of H2 emission from pulsed jets. We also report the first detection of variability in H2 features for a young stellar object (YSO) outflow. It was found that several H2 knots significantly changed their luminosity over the 4 year timebase used to conduct our study. This is in line with current estimates for the cooling time of gas radiating shocked H2 emission in YSO environments.