2004ApJ...607..361D

We present the first contemporaneous 43 and 86 GHz VLBI images of the v=1, J=2⟶1 and J=1⟶0 SiO masers in the Orion KL nebula. Both maser species exhibit the same general morphology of earlier J=1⟶0 maser images, which appear to trace the edges of a bipolar conical outflow. Surprisingly, the J=2⟶1 masers form farther from the central protostar than the J=1⟶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.