SHOCK-ABSORBERS IN BIPOLAR OUTFLOWS

A type of shock which accelerates hydrogen molecules to a high velocity without dissociating is investigated. Such soft C-shocks are characterized by low Alfven Mach numbers and low streaming speeds of the ions through the neutrals. Therefore, a shock in a region of high Alfven speed, upsilon-A can produce wide H-2 line profiles. We show that the shape and width of the H-2 line profiles in the OMC-1 outflow are reproduced by a bow shock of velocity 200-250 km s-1 moving through a dense medium with upsilon-A approximately 46 km s-1. Line ratio data are also successfully modelled from which we infer an H2O abundance < 2 x 10(-4) per hydrogen atom, within the shock. We assert that regions with high Alven speeds are associated with the most energetic bipolar outflows and are essential to the formation of high-mass stars.