VLBI OBSERVATIONS OF THE 6.7 GHZ METHANOL MASERS TOWARD W3(OH)

We have conducted very long baseline interferometric (VLBI) observations of the 6.668 GHz maser transition of interstellar methanol toward the ultracompact H II region W3(OH). We have determined absolute maser positions with an accuracy of 0.05" and produced maps that show that the methanol masers have a distribution similar to the hydroxyl masers in this source. The intrinsic sizes of individual maser spots are almost-equal-to 0.0014" (FWHM), or almost-equal-to 3 AU, and are not significantly affected by interstellar scattering. By comparing maps of the 6.7 and 12.2 GHz methanol maser transitions, we find that the maps can be aligned so that the positions of the strongest 6.7 GHz emission features agree to within a maser spot size (almost-equal-to 0.001") with the positions of strong 12.2 GHz features at the same velocities. This result will provide strong constraints on any excitation mechanism for class II methanol masers.