8.7 GHz hyperfine line of 3He+ in Galactic H II regions

A search for the 8.7 GHz hyperfine line of 3He+ in galactic H II regions has yielded detections in three regions has yielded detections in three regions and significant upper limits for three others. We derive 3He/H abundance ratios of 4 x 10-5 in W43, 1 x 10-4 in W51, and 5 x 10-4 in W3. The upper limits found are 6 x 10-5 in Orion A, and 2 x 10-5 in W49 and M17S. These abundances have been corrected (by up to a factor of 2) for source structure using simple core-halo models. Our detections have line-to-continuum ratios in the range of 10-3 to 10-4. For lines this weak, systematic errors can be much larger than random noise, so we have simultaneously observed many weak recombination lines in order to estimate the magnitude of the systematic errors. We believe the 3He/H abundance for W43 of 4 x 10-5 is our most accurate measurement because it has the smallest structure corrections and the smallest systematic errors