Tracing shock evolution in YSO jets

We have undertaken new observations tracing the evolution of shocks along the best resolved examples of protostellar jets by means of high resolution, deep K-band spectroscopy at UKIRT and NTT. In this paper we analyse trends in H2 excitation within the well collimated jet of HH 212, comprising multiple bows along each flow axis. The aim of our survey is to better understand the origin of the sequence of knots observed along many jets by directly comparing to theoretical models including flow velocity variability and Kelvin-Helmholtz (KH) instabilities. We also investigate any evolution in shock excitation from C-type near the jet source, where ionisation fractions may be low and B-field strengths high, to J-type further downstream where ambient densities decrease. We establish whether fluorescent excitation becomes significant for knots closer to the source in each system. Using these results we can now go on to directly compare our results with model predictions, e.g., knot luminosity, separation and excitation in pulsating jet models (Smith et al. 1997).