Using VLBI to Probe the Orion KL Outflow on AU Scales

We present the first contemporaneous 43 and 86 GHz VLBI images of the v = 1, J = 2 right arrow 1 and J = 1 right arrow 0 SiO masers in the Orion KL nebula. Both maser species exhibit the same general morphology of earlier J = 1 right arrow 0 maser images, which appear to trace the edges of a bipolar conical outflow. Surprisingly, the J = 2 right arrow 1 masers form farther from the central protostar than the J = 1 right arrow 0 masers, a fact not readily explained by current SiO maser pumping models. The average magnitude of offsets between corresponding regions of the two masing transitions is approximately 14% of the total radial extent of the SiO maser emission. This offset indicates that each transition must trace different physical conditions.