Effects of Pre-ionisation in Radiative Shocks II: Application to the Herbig-Haro Objects

In an earlier paper we treated the pre-ionisation problem in shocks over the velocity range $20 < v_{\rm s} < 1000$km/s in a fully self-consistent manner. Here we investigate in detail the effect of the upstream UV photon field generated in the radiative zone of shocks in the range in which hydrogen is only partly ionised ($20 < v_{\rm s} < 150$km/s). We show that, as a result of super-heating in the non-equilibrium pre-shock plasma, both the magnetic parameter and the Mach number of the shock is strongly affected by the pre-ionisation state of the gas which controls to a large extent the radiative spectrum of the shock. We use these models to provide specific line diagnostics for Herbig-Haro objects which allow us to solve for both the pre-shock density and shock velocity, and present detailed models of the HH34 jet which allows us to derive the shock conditions, mass-loss rate, momentum flux and chemical abundances in the jet. We show that the refractory elements, Mg, Ca, Fe and Ni are enhanced by 0.22 dex over the solar values, which provides interesting clues about the jet launching mechanism in pre-main sequence evolution.