Improved Estimates of Galactic H II Region Emission Measures and Filling Factors: Low-Frequency VLA Observations Near Sharpless 53
NAVAL RESEARCH LAB WASHINGTON DC E O HULBURT CENTER FOR SPACE RESEARCH
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VLA observations at 20 and 90 cm of five distant Galactic H II regions in an area including the Sharpless S53 complex have been used to measure their effective sizes and optically thick continuum flux densities. These data have been combined with shorter wavelength, optically thin flux density measurements and electron temperature estimates to determine accurate emission measures where previous results gave only lower limits. Our analysis indicates that existing lower limits to the emission measures often underestimate the true values by more than an order of magnitude. Filling factors for the ionized gas in these H II regions have also been determined and values ranging from 0.03 to 0.50 indicate significant clumping. If these clumps are embedded in a lower density but more widely distributed ionized component, even our much higher emission measures are still lower limits to the true values for the clumps.