Evolution of the structure of the H2O supermaser outburst region in Orion KL

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Abstract
During the period 1979–1999, we investigated the hyperfine structure of the H2O 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 Tb≈1017 K. The velocity of the bipolar outflow is v≈10 km s−1. The rotation velocity of the jet is vrot≈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.

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