Time-dependent shocks and line emission in Herbig-Haro jets

Herbig-Haro jets cool radiatively in a very effective way. Nevertheless, high resolution observations show that temperature along the jet remains above 5,000 K and ionization above 10%, showing a tendency to increase in some regions. Therefore one needs to examine whether there are mechanisms that can successfully balance radiative losses. In this paper we assume that the fraction of the jet that emits the observed spectral lines is small, filling factor similar to 1%, and consider shock dissipation as possible excitation mechanism. We carry out time-dependent numerical simulations of planar perturbations that evolve into shocks and compare the results with observations.