Vol. 579
In section 6. Interstellar and circumstellar matter

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

by J. Bally, A. Ginsburg, D. Silvia, A. Youngblood, A&A 579, A130


The Orion outflow is a collection of high-velocity "fingers" of molecular hydrogen posited to have been launched in a single event ~500 years ago. The authors present new adaptive optics images of these fingers in near-infrared H2 and FeII lines using Gemini's GEMS wide-field adaptive optics imager. They measured proper motions of both the "bullets" - the ionized, Fe-bright tips of the "fingers" - and their wakes. The expansion of the wakes is consistent with pressure-driven expansion of a hot (mega-Kelvin), low-density post-shock medium expanding into a diffuse molecular medium. The morphology of the bullet tips is similarly consistent with single "knots" of material launched ~500 years ago at velocities ~100-300 km/s. The authors present preliminary simulations showing a remarkable morphological similarity to the bullets, which indicates that the simplistic model of a single homogeneous knot launched into a smooth medium captures the relevant physics of the bullets. These observations are consistent with the previously suggested scenario in which the dynamic decay of a non-hierarchical multiple system caused an explosion, and they give hints as to the physical origin of the outflowing material.