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.
