A Molecular Outflow Traced by SiO Masers In Orion-KL

Abstract

We present full resolution (~0.2mas, ~0.1 A.U.) 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 towards its genesis in a bipolar outflow. Water masers which also appear towards Orion-KL are known to share the velocity profile and double peaked characteristics of the SiO maser emission yet form much further 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.