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abstract
A non-LTE analysis of the cometary ultracompact HII region G29.96-0.02 has been completed in the radio recombination lines H110$\alpha$, H76$\alpha$, H66$\alpha$, and H42$\alpha$ at high spatial resolution. The region appears to be an O star moving through a molecular cloud at high speed (roughly 20 km/s). Interaction of the cloud with the ionization front is thought to produce a bow shock (Wood and Churchwell, 1991). Although some gas in the tail appears to spread away from the axis of symmetry, the line peaks, profiles, and velocities agree in general with the bow shock model of Van Buren and Mac Low (1992).
Non-LTE models imply a mean electron temperature of 6800 K, with local densities ranging from $10^5 cm^{-3}$ in the head to $2x10^4 cm^{-3}$ in the tail. Collisional broadening is significant in H110$\alpha$, reducing the peak line amplitude by as much as 70$\%$.}
