Wide‐Angle Wind‐driven Bipolar Outflows: High‐Resolution Models with Application to Source I of the Becklin‐Neugebauer/Kleinmann‐Low OMC‐I Region

Abstract

We carry out high resolution simulations of the inner regions of a wide angle wind driven bipolar outflow using an Adaptive Mesh Refinement code. Our code follows H-He gas with molecular, atomic and ionic components and the associated time dependent molecular chemistry and ionization dynamics with radiative cooling. Our simulations explore the nature of the outflow when a spherical wind expands into a rotating, collapsing envelope. We compare with key observational properties of the outflow system of Source I in the BN/KL region. Our calculations show that the wind evacuates a bipolar outflow cavity in the infalling envelope. We find the head of the outflow to be unstable and that it rapidly fragments into clumps. We resolve the dynamics of the strong shear layer which defines the side walls of the cavity. We conjecture that this layer is the likely site of maser emission and examine its morphology and rotational properties. The shell of swept up ambient gas that delineates the cavity edge retains its angular momentum. This rotation is roughly consistent with that observed in the Source I SiO maser spots. The observed proper motions and line-of-sight velocity are approximately reproduced by the model. The cavity shell at the base of the flow assumes an X-shaped morphology which is also consistent with Source I. We conclude that the wide opening angle of the outflow is evidence that a wide-angle wind drives the Source I outflow and not a collimated jet.