Observations of a curving molecular outflow from V380 Ori-NE: further support for prompt entrainment in protostellar outflows

CO J=3-2 and 4-3 observations of V380 Ori-NE reveal a highly collimated bip olar molecular outflow associated with a jet traced here in H-2 1-0 S(1) li ne emission. The source of the flow is also detected at 450 and 850 mum wit h SCUBA. The combined CO and near-IR observations offer compelling support for the prompt entrainment model of jet-driven molecular outflows. Not only are the H-2 shock fronts spatially coincident with peaks in the CO outflow lobes, but the slope of the mass-velocity distribution in the flow, measur ed here at intervals along both flow lobes, also clearly decreases just beh ind the advancing shock fronts (and towards the ends of the flow lobes), as one would expect if the high-to-low velocity mass fraction was enhanced by the entraining shocks. We also find that both lobes of the CO outflow clearly deviate, by some 20 degrees, from the H-2 jet direction near the source. Both lobes may be bein g deflected at the locations of the observed H-2 shock fronts, where they i mpact dense, ambient material. Alternatively, the almost point-symmetric CO flow pattern could be caused by precession at the source. The submillimetre (submm) data reveal the source of the outflow, V380 Ori-N E. The 450- and 850-mum maps show an elongated peak superimposed on to an e xtensive pedestal of weaker emission. The major axis of the source is orien ted parallel with the inner flow axis. Indeed, weak 850-mum emission is det ected along much of the bipolar outflow, particularly in the southern lobe and towards the southernmost CO intensity peak. The submm 'continuum' data therefore probably trace warm dust and CO associated with the outflow. Thes e data also confirm the status of V380 Ori-NE as a Class I protostar. Overall, the orientation, simplicity and symmetry of this outflow, combined with the remarkable strength of the high-velocity line-wing emission in co mparison to the ambient emission, make this system a perfect laboratory for future detailed studies of bipolar molecular outflows and their associatio n with collimated jets from young, deeply embedded protostars.