Jet rotation investigated in the near-ultraviolet with HST/STIS
  We present results of the second phase of our near-ultraviolet investigation
into protostellar jet rotation using HST/STIS. We obtain long-slit spectra at
the base of five T Tauri jets to determine if there is a difference in radial
velocity between the jet borders which may be interpreted as a rotation
signature. These observations are extremely challenging and push the limits of
current instrumentation, but have the potential to provide long-awaited
observational support for the magneto-centrifugal mechanism of jet launching in
which jets remove angular momentum from protostellar systems. We successfully
detect all five jet targets (from RW Aur, HN Tau, DP Tau and CW Tau) in several
near-ultraviolet emission lines, including the strong Mg II doublet. However,
only RW Aur's bipolar jet presents sufficient signal-to-noise for analysis. The
approaching jet lobe shows a difference of 10 km/s in a direction which agrees
with the disk rotation sense, but is opposite to previously published optical
measurements for the receding jet. The near-ultraviolet difference is not found
six months later, nor is it found in the fainter receding jet. Overall, in the
case of RW Aur, differences are not consistent with a simple jet rotation
interpretation. Indeed, given the renowned complexity and variability of this
system, it now seems likely that any rotation signature is confused by other
influences, with the inevitable conclusion that RW Aur is not suited to a jet
rotation study.
