COMETARY AND BIPOLAR ULTRACOMPACT H-II-REGIONS

Mass-loaded models can explain how a cometary morphology, ultracompact I-In region can arise around a stationary star. The star is located i n a density gradient in the mass-loading sources. Continuous mass-loss from the clumps embedded in the ionized gas allows the region to rema in compact. The wind and radiation field from the central star set up a fully supersonic flow that is bounded by a recombination front. We d evelop the models further by calculating the velocity and density stru cture in detail for a variety of viewing angles, mass-loading laws and density scaleheights. The results are compared with observational wor k, and the agreements and differences are highlighted. We extend this model to show how a massive star located in a dense molecular ridge ca n give rise to a bipolar or ring morphology, depending on the viewing angle.