A Molecular Outflow Traced by S[CLC]i[/CLC]O Masers in Orion KL

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Abstract
We present full-resolution (~0.2 mas, ~0.1 AU) Very Long Baseline Interferometry maps of the v=1, J=1→0 SiO masers in the Orion KL nebula. The morphology and turbulent nature of the maser emission argues against models in which the masers form in an expanding and rotating protostellar disk. Rather, we find that the symmetry evident in the SiO maser emission points toward its genesis in a bipolar outflow. Water masers that also appear toward Orion KL are known to share the velocity profile and double-peaked characteristics of the SiO maser emission yet form much farther away from the protostar. We link the water masers to our present results by proposing that both species of maser form around a flared molecular outflow of roughly constant velocity.