  We report the first near-infrared detection of the bipolar microjet from
TTauri star ThA 15-28 (aka Th 28). Spectra were obtained with VLT/ISAAC for the
slit both perpendicular and parallel to the flow to examine jet kinematics and
gas physics within the first arcsecond from the star. The jet was successfully
detected in both molecular and atomic lines. The H_2 component was found to be
entirely blueshifted around the base of the bipolar jet. It shows that only the
blue lobe is emitting in H_2 while light is scattered in the direction of the
red lobe, highlighting an asymmetric extinction and/or excitation between the
two lobes. Consistent with this view, the red lobe is brighter in all atomic
lines. Interestingly, the jet was detected not only in [Fe II], but also in Br
gamma and Pa beta lines. Though considered tracers mainly of accretion, we find
that these high excitation hydrogen permitted lines trace the jet as far as 150
AU from the star. This is confirmed in a number of ways: the presence of the
[Fe II] 2.13 micron line which is of similarly high excitation; H I velocities
which match the jet [Fe II] velocities in both the blue and red lobe; and high
electron density close to the source of >6x10^4 cm^-3 derived from the [Fe II]
1.64,1.60 micron ratio. These near-infrared data complement HST/STIS optical
and near-ultraviolet data for the same target which were used in a jet rotation
study, although no rotation signature could be identified here due to
insufficient angular resolution. The unpublished HST/STIS H alpha emission is
included here along side the other H I lines. Identifying Br gamma and Pa beta
as tracers of ejection is significant because of the importance of finding
strong near-infrared probes close to the star, where forbidden lines are
quenched, which will help understand accretion-ejection when observed with high
spatial resolution instruments such as VLTI/AMBER.
