Abstract
The Orion-KL nebula is the closest (450pc) site of high-mass star formation and exhibits powerful outflows associated with protostars. It is also one of only three known star forming regions to exhibit SiO maser emission. Emission in three SiO maser transitions (v=1 J=1 → 0, v=1 J=2 → 1, and v=2 J=1 → 0) imaged by VLBI exhibits an “X” morphology suggesting that the Orion masers form along the outlines of two opposing conical outflows to the NW and SE. At the center of this “X”, VLA observations find emission from an HII region presumably associated with a young star whose wind drives the outflow. The SiO masers probably form along the interface between the stellar wind and surrounding parent cloud. We find that SiO maser emission from different transitions preferentially occurs at different radii from the central star implying that the masers are tracers for physical conditions in the wind-cloud interaction region. On the smallest scales, some individual maser features in each transition overlap both spatially and in velocity providing strong evidence that more than one transition can mase within the same volume of gas.
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