Evolution of the Structure of the H_2O Supermaser Outburst Region in Orion KL

摘要

During the period 1979-1999, we investigated the hyperfine structure of the H_2O supermaser region located in the core of the molecular cloud OMC-1 in Orion KL. The angular resolution is 0.1 mas, which corresponds to 0.045 AU. The detected structure, which consists of a central object, an accretion disk, a bipolar outflow, and an envelope, corresponds to the initial formation stage of a low-mass star. The accretion disk is at the stage of separation into groups of concentric rings. The bipolar outflow is a neutral, highly collimated jet of accreted material that includes H2O molecules and dust grains in the icy envelope. The injector is a bright compact source with a size < 0.05 AU and a brightness temperature T_b ≈ 10~(17) K. The velocity of the bipolar outflow is v ≈ 10 km s~(-1). The rotation velocity of the jet is v_(rot) ≈ 1.5 km s~(-1). The jet has the shape of a conical helix due to the precession of the rotation axis. Occasionally, dense blobs (comet-shaped bullets) are ejected. The envelope amplifies the radio emission from the structures in a ～0.5 km s~(-1) maser window band with velocities v ≈ 7.65 km s~(-1) by more than two orders of magnitude.