  HH 666 is an externally irradiated protostellar outflow in the Carina Nebula
for which we present new near-IR [Fe II] spectra obtained with the FIRE
spectrograph at Magellan Observatory. Earlier H{\alpha} and near-IR [Fe II]
imaging revealed that the two emission lines trace substantially different
morphologies in the inner ~40" of the outflow. H{\alpha} traces a broad cocoon
that surrounds the collimated [Fe II] jet that extends throughout the parent
dust pillar. New spectra show that this discrepancy extends to their
kinematics. Near-IR [Fe II] emission traces steady, fast velocities of +/- 200
km/s from the eastern and western limbs of the jet. We compare this to a
previously published H{\alpha} spectrum that reveals a Hubble-flow velocity
structure near the jet-driving source. New, second-epoch HST/ACS H{\alpha}
images reveal the lateral spreading of the H{\alpha} outflow lobe away from the
jet axis. H{\alpha} proper motions also indicate a sudden increase in the
mass-loss rate ~1000 yr ago, while steady [Fe II] emission throughout the inner
jet suggests that the burst is ongoing. An accretion burst sustained for ~1000
yr is an order of magnitude longer than expected for FU Orionis outbursts, but
represents only a small fraction of the total age of the HH 666 outflow.
Altogether, available data suggests that [Fe II] traces the highly collimated
protostellar jet while H{\alpha} traces the entrained and irradiated outflow.
HH 666 appears to be a missing link between bare jets seen in H II regions and
entrained molecular outflows seen from embedded protostars in more quiescent
regions.
