Abstract
Reipurth et al. (2002) have obtained very detailed proper motions of the HH 34S bowshock using Hubble Space Telescope (HST) images. We find that these proper motions can be used to reconstruct the position-dependent shock velocity and the flow velocity ahead of the bowshock. From this excercise, we obtain shock velocities in the 60 to 120 km s-1 range, in qualitative agreement with previous determinations based on the analysis of line profiles and line ratios. We also deduce the presence of a ≈ 200 km s-1 flow directly ahead of HH 34S, extending out to ~ 10'' on each side of the outflow axis. We interpret this flow as the wake left behind by previous outflow events, and show that a variable ejection velocity gasdynamic jet simulation does reproduce the properties of this flow in a convincing way.
