On the composition of H II regions in southern galaxies - I. NGC 300 and 1365.

AAT/IPCS spectra were obtained from six H II regions at differing radial distances from the center of the Scd galaxy NGC 300 and from three H II regions in the giant barred spiral NGC 1365 which has an active nucleus. The spectra were analyzed to determine abundances of the elements represented by observed emission lines from a combination of electron temperatures based on various weak temperature-sensitive lines and interpolation between photoionization models, using the sum of (O II) and (O III) intensities relative to the H beta emission to select plausible model parameters. The NGC 300 and NGC 1365 abundances are described, noting that the abundances of the latter are fairly close to solar. One object in NGC 300 is unusual in having stronger (O II) than usually found in giant H II regions in Scd galaxies, and neon, sulphur, and argon abundances relative to oxygen are close to those of Orion and the Magellanic Clouds, while the He/H ratio appears slightly lower than in Orion.