  The new 8.4m LBT adaptive secondary AO system, with its novel pyramid
wavefront sensor, was used to produce very high Strehl (75% at 2.16 microns)
near infrared narrowband (Br gamma: 2.16 microns and [FeII]: 1.64 microns)
images of 47 young (~1 Myr) Orion Trapezium theta1 Ori cluster members. The
inner ~41x53" of the cluster was imaged at spatial resolutions of ~0.050" (at
1.64 microns). A combination of high spatial resolution and high S/N yielded
relative binary positions to ~0.5 mas accuracies. Including previous speckle
data, we analyse a 15 year baseline of high-resolution observations of this
cluster. We are now sensitive to relative proper motions of just ~0.3 mas/yr
(0.6 km/s at 450 pc) this is a ~7x improvement in orbital velocity accuracy
compared to previous efforts. We now detect clear orbital motions in the theta1
Ori B2/B3 system of 4.9+/-0.3 km/s and 7.2+/-0.8 km/s in the theta1 Ori A1/A2
system (with correlations of PA vs. time at >99% confidence). All five members
of the theta1 Ori B system appear likely as a gravitationally bound
"mini-cluster". The very lowest mass member of the theta1 Ori B system (B4;
mass ~0.2 Msun) has, for the first time, a clearly detected motion (at
4.3+/-2.0 km/s; correlation=99.7%) w.r.t B1. However, B4 is most likely in an
long-term unstable (non-hierarchical) orbit and may "soon" be ejected from this
"mini-cluster". This "ejection" process could play a major role in the
formation of low mass stars and brown dwarfs.
