Abundances in H II regions at the edge of the Galaxy

Optical spectra, supplemented by some observations of radio recombination lines, have been used to estimate the abundances of helium, oxygen, nitrogen, sulfur, and argon in 18 H II regions in the outer Galaxy. Assuming that R0 (the distance from the center of the Galaxy to the sun) is 8.5 kpc, these H II regions are located between 11.5 and 17.9 kpc from the Galactic center and include many of the most distant (from the center) H II regions known in our Galaxy. The single most striking result of these observations is the apparent high nitrogen abundances in the H II regions at the outer edge of the visible disk of the Galaxy. 40 refs