Using VLBI to Probe the Orion KL Outflow on AU Scales

We present the first contemporaneous 43 and 86 GHz VLBI images of thev=1, J=2-->1 and J=1-->0 SiO masers in the Orion KL nebula. Bothmaser species exhibit the same general morphology of earlier J=1-->0maser images, which appear to trace the edges of a bipolar conicaloutflow. Surprisingly, the J=2-->1 masers form farther from thecentral protostar than the J=1-->0 masers, a fact not readilyexplained by current SiO maser pumping models. The average magnitude ofoffsets between corresponding regions of the two masing transitions is