He-3 in the Milky Way interstellar medium: Summary of relevant observations

We summarize spectral line and continuum observations of a sample of 21 Galactic H II regions made at 3.46 cm wavelength during the past 14 years as part of a program to measure the abundance of He-3 in the Milky Way interstellar medium. Converting the observed He-3(+) column density into an abundance ratio relative to hydrogen depends on the density and ionization structure of each nebula. The observations needed to model our sources were made with the NRAO 140 foot (43 m), NRAO VLA, and MPIfR 100 m telescopes. Here we describe and compile our measurements of the He-3(+) emission line as well as those of various recombination transitions of H, He, and C. We also summarize the continuum database which includes single-dish observations and interferometer maps.