Effects of Preionization in Radiative Shocks. II. Application to the Herbig–Haro Objects

Abstract

In an earlier paper we treated the preionization problem in shocks over the velocity range 20 km s −1  km s −1  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 ionized 20 km s −1  ( km s −1 ). We show that, as a result of superheating in the nonequilibrium preshock plasma, both the magnetic parameter and the Mach number of the shock are strongly affected by the preionization 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 preshock density and shock velocity, and we present detailed models of the HH 34 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.