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 speed of the ions through the neutrals. Therefore, a shock in a region of high Alfven speed, υA can produce wide H2 line profiles. We show that the shape and width of the H2 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 υA∼46 km s-1. Line ratio data are also successfully modelled from which we infer an H2O abundance <2x10-4 per hydrogen atom, within the shock. (author)