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[71.06] Considerations of Clumpiness for the Free-Free Radio Spectra of Compact HII Regions

R. Ignace (East Tennessee State University), E. B. Churchwell (University of Wisconsin)

Considering a uniform spherical clump of gas, we derive analytically the free-free emission from a single isolated cloud. Such a clump produces a radio continuum spectrum with a power-law slope (F_\nu \propto \nu^\alpha) that varies from +2 when optically thick (low frequency) to -0.11 when optically thin (high frequency). Ignoring the effects of shadowing, the spectrum from an ensemble of such clumps is governed solely by their optical depth distribution. In some circumstances a power-law slope that is intermediate between +2 and -0.11 can persist over a significant bandwidth in frequency. We apply our model to reproduce successfully the radio spectrum of the hypercompact HII region W49N-B2, which exhibits a continuum slope of \alpha \approx +0.9 between 3.3~mm and 13~mm.

This research has been supported by NSF grants AST-9986548 and AST-0241493.

The author(s) of this abstract have provided an email address for comments about the abstract: ignace@mail.etsu.edu

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.