  In recent years, there has been a number of detections of gradients in the
radial velocity profile across jets from young stars. The significance of these
results is considerable. They may be interpreted as a signature of jet rotation
about its symmetry axis, thereby representing the only existing observational
indications supporting the theory that jets extract angular momentum from
star-disk systems. However, the possibility that we are indeed observing jet
rotation in pre-main sequence systems is undergoing active debate. To test the
validity of a rotation argument, we must extend the survey to a larger sample,
including younger sources. We present the latest results of a radial velocity
analysis on jets from Class 0 and I sources, using high resolution data from
the infrared spectrograph GNIRS on GEMINI South. We obtained infrared spectra
protostellar jets HH 34, HH 111-H, HH 212 NK1 and SK1. The [Fe II] emission was
unresolved in all cases and so Doppler shifts across the jet width could not be
accessed. The H_2 emission was resolved in all cases except HH 34. Doppler
profiles across the molecular emission were obtained, and gradients in radial
velocity of typically 3 km/s identified. Agreement with previous studies
implies they may be interpreted as jet rotation, leading to toroidal velocity
and angular momentum flux estimates of 1.5 km/s and 1x10^-5 M_odot/yr AU km/s
respectively. However, caution is needed. For example, emission is asymmetric
across the jets from HH 212 suggesting a more complex interpretation is
warranted. Furthermore, observations for HH 212 and HH 111-H are conducted far
from the source implying external influences are more likely to confuse the
intrinsic flow kinematics. These observations demonstrate the difficulty of
conducting this study from the ground, and highlight the necessity for high
angular resolution via adaptive optics or space-based facilities.
