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| - The Orion fingers: Near-IR adaptive optics imaging of an explosive protostellar outflow
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| - Aims. Adaptive optics (AO) 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 H 2, [Fe ii], and broad-band Ks obtained with the Gemini South multi-conjugate AO system GeMS and near-IR imager GSAOI are presented. The images reach resolutions of 0.08 to 0.10 ′′, close to the 0.07 ′′ diffraction limit of the 8-m telescope at 2.12 μm . 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 H 2 and [Fe ii] features with unprecedented precision. The images are compared with numerical simulations of compact, high-density clumps moving ~10 3 times their own diameter through a lower density medium at Mach 10 3. Results. Several sub-arcsecond H 2 features and many [Fe ii] “fingertips” on the projected outskirts of the flow show proper motions of ~300 km s -1. High-velocity, sub-arcsecond H 2 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 yr 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.
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