We present the first scientific images obtained with a deformable secondary mirror adaptive optics system. We utilized the 6.5m MMT AO system to produce high-resolution (FWHM=0.07 ′′ ) near infrared (1.6µm) images of the young (∼ 1 Myr) Orion Trapezium θ 1 Ori cluster members. A combination of high spatial resolution and high signal to noise allowed the positions of these stars to be measured to within ∼ 0.003 ′′ accuracies. We also present slightly lower resolution (FWHM∼0.085 ′′ ) images from Gemini with the Hokupa'a AO system as well. Including previous speckle data (Weigelt et al. 1999), we analyze a six year baseline of high-resolution observations of this cluster. Over this baseline we are sensitive to relative proper motions of only ∼ 0.002 ′′ /yr (4.2 km/s at 450 pc). At such sensitivities we detect orbital motion in the very tight θ 1 Ori B 2 B 3 (52 AU separation) and θ 1 Ori A 1 A 2 (94 AU separation) systems. The relative velocity in the θ 1 Ori B 2 B 3 system is 4.2 ± 2.1 km/s. We observe 16.5 ± 5.7 km/s of relative motion in the θ 1 Ori A 1 A 2 system. These velocities are consistent with those independently observed by Schertl et al. (2003) with speckle interferometry, giving us confidence that these very small (∼ 0.002 ′′ /yr) orbital motions are real. All five members of the θ 1 Ori B system appear likely gravitationally bound (B 2 B 3 is moving at ∼ 1.4 km/s in the plane of the sky w.r.t. B 1 where V esc ∼ 6 km/s for the B group). The very lowest mass member of the θ 1 Ori B system (B 4 ) has K ′ ∼ 11.66 and an estimated mass of ∼ 0.2M ⊙ . There was very little motion (4 ± 15 km/s) detected of B 4 w.r.t B 1 or B 2 , hence B 4 is possibly part of the θ 1 Ori B group. We suspect that if this very low mass member is physically associated it most likely is in an unstable (non-hierarchical) orbital position and will soon be ejected from the group. The θ 1 Ori B system appears to be a good example of a star formation "mini-cluster" which may eject the lowest mass members of the cluster in the near future. This "ejection" process could play a major role in the formation of low mass stars and brown dwarfs.

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