Probing jets from young embedded sources: clues from HST near-IR [Fe II]
  images
  We present near-infrared [Fe II] images of four Class 0/I jets (HH 1/2, HH
34, HH 111, HH 46/47) observed with the Hubble Space Telescope Wide Field
Camera 3. The unprecedented angular resolution allows us to measure proper
motions, jet widths and trajectories, and extinction along the jets. In all
cases, we detect the counter-jet which was barely visible or invisible at
shorter wavelengths. We measure tangential velocities of a few hundred km/s,
consistent with previous HST measurements over 10 years ago. We measure the jet
width as close as a few tens of au from the star, revealing high collimations
of about 2 degrees for HH 1, HH 34, HH 111 and about 8 degrees for HH 46, all
of which are preserved up to large distances. For HH 34, we find evidence of a
larger initial opening angle of about 7 degrees. Measurement of knot positions
reveals deviations in trajectory of both the jet and counter-jet of all
sources. Analysis of asymmetries in the inner knot positions for HH 111
suggests the presence of a low mass stellar companion at separation 20-30 au.
Finally, we find extinction values of 15-20 mag near the source which gradually
decreases moving downstream along the jet. These observations have allowed us
to study the counter-jet at unprecedented high angular resolution, and will be
a valuable reference for planning future JWST mid-infrared observations which
will peer even closer into the jet engine.
