VLA high-sensitivity He-4 imaging of Galactic HII regions

We have carried out 8.3 GHz hydrogen and helium radio recombination line an d continuum observations of three Galactic H II regions with the NRAO 140 F oot Telescope and the Very Large Array. These observations measure the spat ial variations in the singly ionized helium-to-hydrogen abundance ratio, He -4(+)/H+ (y(+)), and probe for any localized enhancements in y(+). The thre e observed regions (W43, NGC 6334A, and K3-50) are morphologically complex, and high-resolution, wide field observations are crucial to measure the he lium abundances on scales that would be associated with individual massive stars or clusters of stars. The nearly constant y(+) value across the W43 s ource ([y(+)](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 He-3, w hich is measured in the Galaxy via a singly ionized hyperfine transition. L ocalized enhancements in the y(+) value have been detected in both NGC 6334 A (y(+) = 20% +/- 4%) and K3-50A (y(+) = 24% +/- 5%). The He-4 abundance re sults are discussed along with other measurements of the physical propertie s of these H II regions, such as the kinematics and excitation.