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[112.24U] Physical parameters and possible masing in Galactic ultracompact HII regions

C. Kasm ( U. of Florida and the Maria Mitchell Obs.)

Six ultracompact HII regions, G5.89-0.39, G10.62-0.38, G15.04-0.68, G34.26+0.15, G35.20-1.74, and G45.07+0.13, were observed in several radio recombination lines from H30-alpha to H45 alpha on the 12-meter millimeter radio telescope at Kitt Peak, Arizona. In the framework of the standard model of optically thin radio recombination line emission, the following physical parameters of each region were derived: electron temperature, turbulent velocity, number density, mass of ionized hydrogen, emission measure, and excitation parameter. The primary goal of this study, however, was to search for possible signatures of maser amplification in these lines. While no signs of high gain amplification were found, such as narrow bright spectral components, the deduced physical parameters of at least one source, G15.04-0.68, indicate favorable conditions for low gain masing. The necessary corrections of the physical parameters derived for the optically thin case are discussed. This project was supported by the NSF/REU grant AST-0097694 and the Nantucket Maria Mitchell Association.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.