CHEMICAL-COMPOSITIONS OF H-II REGIONS IN THE TRIANGULUM SPIRAL, M33

Measurements of 12 H II regions secured with the Robinson-Wampler Image Tube Scanner at the Shane Telescope, Lick Observatory cover the spectral range λ λ 3700-7600. The distances of these regions from the nucleus range from 1 to 6 kpc. These data are analysed to establish plasma diagnostics and chemical compositions. In a manner similar to that previously employed for studies of the Magellanic Clouds, theoretical models are used as interpolation devices to establish ionization correction factors for S, Cl and Ar. Except for helium, the N(element) /N(H) ratios fall off with increasing radial distance with closely similar rates. Consequently, the ratios not only of nitrogen, but also neon, sulphur and argon, with respect to oxygen, remain essentially constant. The following log N(element)/N(oxygen) are found: N = -1.25, Ne = -0.77, S = -1.5, Cl = -3.6 and Ar = -2.4. © 1981 Royal Astronomical Society.