The abundances of O, S, Cl, N, Ar, He and C in seven Galactic HII regions

An analysis of CCD spectra in the range lambda lambda 4200-8775, obtained a t several positions of seven bright Galactic H II regions, with galactocent ric distances in the range 6-10 kpc, is presented. Temperatures, densities and ionic abundances an calculated for all the positions, and the relative trends followed by these parameters are established. It is shown that all t hese H II regions share the same abundances of O, S, Cl, N, Ar and He, with in their expected uncertainties, a result which is consistent with a flat o r small abundance gradient in the Galactic disc within +/-2 kpc from the Su n, as suggested by some studies of the abundances in H II regions and B-typ e stars. The same set of homogeneously derived ionic abundances is also use d to test the accuracy of the fractional ionization predicted by available grids of models for photoionized nebulae.