An accretion disk, a bipolar outflow, and an envelope—A structure that accompanies the formation of a protostar

Abstract

We analyze the superfine structure of the supermaser H2O emission region in Orion KL over the period 1979–1999. The angular resolution reached 0.1 mas, which corresponds to 0.045 AU at a distance to Orion KL of 450 pc. We determined the velocity of the local standard of rest, V LSR = 7.65 km s−1. The formation of a protostar is accompanied by a structure that consists of an accretion disk, a bipolar outflow, and a surrounding envelope. The disk is at the stage of separation into protoplanetary rings. The disk plane is warped like the brim of a hat. The disk is 27 AU in diameter and ∼0.3 AU in thickness. The rings contain ice granules. Radiation and stellar wind sublimate and blow away the water molecules to form halos around the rings, maser rings. The radiation from the rings is concentrated in the azimuthal plane, and its directivity reaches 10−3. The relative velocities of the rings located in the central part of the disk 15 AU in diameter correspond to rigid-body rotation, V rot = ΩR. The rotation period is T ≈ 170 yr. The injector is surrounded by a toroidal structure 1.2 AU in diameter. The diameter of the injected flow does not exceed 0.05 AU. A highly collimated bipolar outflow with a diameter of ∼0.1 AU is observed at a distance as large as 3 AU. Precession of the injector axis with a period of ∼10 yr forms a spiral flow structure. The flow velocity is ∼10 km s−1. The kinetic energy of the accreting matter and the disk is assumed to be transferred to the bipolar outflow, causing the rotation velocity distribution of the rings to deviate from the Keplerian velocity. The surrounding envelope amplifies the emission from the structure at a velocity of 7.65 km s−1 in a band of ∼0.5 km s−1 by more than two orders of magnitude, which determines the supermaser emission.