High-resolution near-infrared observations of Herbig-Haro flows - II. Echelle spectroscopy

We use line profile data to probe the physical conditions associated with m olecular hydrogen features in four Herbig-Haro (HH) flows: HH 7-11, 33/40, 26 and 212. We compare these kinematic data with new H-2 images and proper motion measurements presented in a companion paper (Paper I) by Chrysostomo u et al. We find in these combined data evidence for bow shocks and turbulent mixing layers. HH 7 and 33 represent spectacular examples of resolved bow shocks; double-peaked H-2 emission profiles are observed in the flanks of both tar gets. HH 26C is also thought to be a bow shock, although one that has under gone considerable fragmentation during its lifetime [based on its current p roper motion (from Paper I), this bow has a dynamical age of roughly 600 (/- 130) yr]. HH 40 and 26A instead seem to represent turbulent boundary lay ers between the HH flows and their ambient surroundings; both features have very low proper motions. However, although the H-2 profiles in HH 40 are n arrow and symmetric, as one might expect from a turbulent spectrum of unres olved shocks, in HH 26A we see complex structure in position-velocity space . This suggests that shocks generated in the HH 26A turbulent boundary are resolved in these data. The associated curved shocks thus generate more asy mmetric profiles and, in some cases, double-peaked profiles. In HH 212 we see narrow, symmetric profiles in the knots along the flow axi s, as well as clear evidence of acceleration along the jet. The spatial sym metry evident in images of this bipolar jet is also reflected in the veloci ties of the knots. The bow shocks NB1/2 and SB1 in HH 212 also possess bow- shock-like profiles in our position-velocity plots. Transverse velocity gra dients in the knots provide some evidence for jet rotation. The rotation is consistent with the necessary extraction of angular momentum from the unde rlying rotating disc to enable the continued accretion of material on to th e protostar. Lastly, we return to the issue of whether H-2 shock features accelerate mol ecular gas to form the massive bipolar outflows usually traced in CO. Compa rison of the mass fluxes measured in each HH object (from our H-2 data) wit h mass outflow rates typical of 'CO' outflows suggests that this is indeed the case.