The Orion Fingers: Near-IR Adaptive Optics Imaging of an Explosive
  Protostellar Outflow
  Aims. Adaptive optics images are used to test the hypothesis that the
explosive BN/KL outflow from the Orion OMC1 cloud core was powered by the
dynamical decay of a non-hierarchical system of massive stars. Methods.
Narrow-band H2, [Fe II], and broad-band Ks obtained with the Gemini South
multi-conjugate adaptive optics (AO) system GeMS and near-infrared imager GSAOI
are presented. The images reach resolutions of 0.08 to 0.10", close to the
0.07" diffraction limit of the 8-meter telescope at 2.12 microns. Comparison
with previous AO-assisted observations of sub-fields and other ground-based
observations enable measurements of proper motions and the investigation of
morphological changes in H2 and [Fe II] features with unprecedented precision.
The images are compared with numerical simulations of compact, high-density
clumps moving ~1000 times their own diameter through a lower density medium at
Mach 1000. Results. Several sub-arcsecond H2 features and many [Fe II]
'fingertips' on the projected outskirts of the flow show proper motions of ~300
km/s. High-velocity, sub-arcsecond H2 knots ('bullets') are seen as far as 140"
from their suspected ejection site. If these knots propagated through the dense
Orion A cloud, their survival sets a lower bound on their densities of order
10^7 cm^-3, consistent with an origin within a few au of a massive star and
accelerated by a final multi-body dynamic encounter that ejected the BN object
and radio source I from OMC1 about 500 years ago. Conclusions. Over 120
high-velocity bow-shocks propagating in nearly all directions from the OMC1
cloud core provide evidence for an explosive origin for the BN/KL outflow
triggered by the dynamic decay of a non-hierarchical system of massive stars.
Such events may be linked to the origin of runaway, massive stars.
