VLA OBSERVATIONS OF HIGHLY EXCITED OH ABSORPTION TOWARD W3(OH)

We have used the Very Large Array (VLA) to map the two main hyperfine lines of the highly excited (II3/2)-I-2, J = 9/2 level of OH toward the ultracompact HII region W3(OH) with high angular (0 ''.33) and spectral (0.62 km s(-1)) resolution. These transitions have frequencies near 23.8 GHz and, with energies around 500 K above the ground-state, probe hot gas in the molecular environment of the ultracompact HII region. Both lines are seen in absorption against the western half of the HII region with an angular extent and a clumpy structure similar to that of OH transitions in the (II1/2)-I-2 energy ladder, which have been previously observed with the VLA at comparable resolution. In contrast to the latter, we find for most of the area over which the OH lines are detected that the excitation of the J = 9/2 level apparently does not show strong deviations from LTE, except for a compact region near its northeastern boundary, where we tentatively detect weak maser emission in the F = 4 --> 4 transition. We have also produced a 23.8 GHz continuum map of W3(OH) that is in good agreement with previous VLA maps at similar frequencies.