AAS 199th meeting, Washington, DC, January 2002
Session 124. H II Regions
Display, Thursday, January 10, 2002, 9:20am-4:00pm, Monroe/Lincoln

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[124.02] Arecibo Observations of Formaldehyde and Radio Recombination Lines Toward Ultracompact HII Regions

E. Araya (University of Puerto Rico at Rio Piedras), P. Hofner (University of Puerto Rico at Rio Piedras and Arecibo Observatory, NAIC/Cornell University), E. Churchwell (University of Wisconsin-Madison), S. Kurtz (UNAM)

We report observations of the H110\alpha radio recombination line and H2CO (110 -- 111) toward 21 ultracompact HII regions with the Arecibo 305-m Radiotelescope. We detect the H110\alpha line in 20 sources, and for each of these we also detect a H2CO absorption feature at nearly the same velocity, demonstrating the association between molecular and ionized gas. We determine kinematic distances, and resolve the distance ambiguity for all observed HII regions, as well as for 19 intervening molecular clouds. A plot of the galactic distribution of these objects traces part of the spiral structure in the first galactic quadrant. We compare flux densities and velocities as measured with the Arecibo Telescope with interferometric measurements of our sample of ultracompact HII regions. In general, the single-dish fluxes exceed the interferometric values, consistent with an extended component of radio continuum emission.

This research was partially supported by NSF grant EPS-9874782 as well as UNAM DGAPA grant 117799.

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