VLA High-Sensitivity [TSUP]4[/TSUP]H[CLC]e[/CLC] Imaging of Galactic H [CSC]ii[/CSC] Regions

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Abstract
We have carried out 8.3 GHz hydrogen and helium radio recombination line and continuum observations of three Galactic H II regions with the NRAO 140 Foot Telescope and the Very Large Array. These observations measure the spatial variations in the singly ionized helium-to-hydrogen abundance ratio, 4He+/H+ (y+), and probe for any localized enhancements in y+. The three observed regions (W43, NGC 6334A, and K3-50) are morphologically complex, and high-resolution, wide field observations are crucial to measure the helium abundances on scales that would be associated with individual massive stars or clusters of stars. The nearly constant y+ value across the W43 source (W43 = 7.7% ± 1%) indicates that any ionization correction over the spatial scales investigated is small. Such ionization corrections are important for calculating total abundances of the light element 3He, which is measured in the Galaxy via a singly ionized hyperfine transition. Localized enhancements in the y+ value have been detected in both NGC 6334A (y+ = 20% ± 4%) and K3-50A (y+ = 24% ± 5%). The 4He abundance results are discussed along with other measurements of the physical properties of these H II regions, such as the kinematics and excitation.

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