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S.S. Doeleman, C.J. Lonsdale, R.B. Phillips, R.E. Barvainis (Haystack Observatory), L. J. Greenhill (Harvard - CfA)
We present full resolution (~.2mas, ~.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. We compare these images to spot maps made using contemporaneous 86GHz-VLBI of the v=1, J=2-1 SiO maser transition. The resolution of the 86GHz maps allows us to discuss the cospatiality of the two transitions on 10mas (5 AU at a distance of 450pc) scales and, hence, the pumping mechanisms responsible for the masing action.