Ultracompact HII Regions: A Molecular Point of View

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Session 30 -- Star Formation, Molecular Clouds and HII Regions
Display presentation, Tuesday, 31, 1994, 9:20-6:30

[30.13] Ultracompact HII Regions: A Molecular Point of View

S. Kurtz (UNAM), E. Churchwell (University of Wisconsin-Madison), D.O.S. Wood (NRAO), P. Myers (CfA)

Ultracompact (UC) HII regions manifest themselves through infrared emission from circumstellar dust, the radio continuum of their dense, ionized gas, and by remnant molecular gas from which the massive stars recently formed. Using the IRAS Point Source Catalog, Wood \& Churchwell (1989) identified $\sim$1600 UC HII candidates. Since then, radio continuum surveys have identified over 200 such nebulae. But until now, no survey has been made of the dense, circumnebular molecular gas in which these stars are embedded.

We present results from a CO molecular line survey made with the 14m telescope of the Five College Radio Astronomy Observatory. Four hundred candidate UC HII regions, selected from the Point Source Catalog, were imaged in the $^{12}$CO line. Sixty-nine percent of these have CO emission localized near the IRAS position, as expected for UC HII regions. We obtain kinematic distances and luminosities for 117 sources and use this information to estimate the spectral types of the embedded stars. We discuss the performance of the far infrared color selection critera and possible kinematic structures seen within the data. Seventy-four outflow candidates are identified, which may significantly increase the number of known massive star outflows.

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