The Orion fingers: Near-IR adaptive optics imaging of an explosive protostellar outflow^⋆

¹ Department of Astrophysical and Planetary SciencesUniversity of Colorado, UCB 389 Boulder CO 80309 USA
e-mail: John.Bally@colorado.edu
² ESO Headquarters, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
³ NSF Astronomy and Astrophysics Postdoctoral Fellow, Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA

Received: 28 September 2014
Accepted: 5 February 2015

Abstract

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 H₂, [Fe ii], and broad-band K_s 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 H₂ and [Fe ii] features with unprecedented precision. The images are compared with numerical simulations of compact, high-density clumps moving ~10³ times their own diameter through a lower density medium at Mach 10³.

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^-1. 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 10⁷ 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.