Radiative Bow Shock Models of Herbig-Haro Objects

The bow-shock models of HH objects presently constructed from a collection of 43 radiative-planar-shock models are used to predict the line ratios and line profiles expected from HH objects. It is found that a radiating-bow-shock model formed around a 'bullet' of dense gas plowing into the ambient medium accounts for existing observations sufficiently well to constitute a unifying model. For particular bow-shock orientations, double-peaked profiles are predicted in spatially unresolved spectra. A simple analytic formula is presented that can be used to estimate the shock velocity and bow-shock orientation from a single high-resolution observation of a low-excitation line. 63 references.