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Astron. Astrophys. 351, 1075-1086 (1999)


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

M. Rodríguez

Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Canarias, Spain (mrodri@ll.iac.es)

Received 12 July 1999 / Accepted 27 September 1999

Abstract

An analysis of CCD spectra in the range [FORMULA], obtained at several positions of seven bright Galactic HII regions, with galactocentric distances in the range 6-10 kpc, is presented. Temperatures, densities and ionic abundances are calculated for all the positions, and the relative trends followed by these parameters are established. It is shown that all these HII regions share the same abundances of O, S, Cl, N, Ar and He, within their expected uncertainties, a result which is consistent with a flat or small abundance gradient in the Galactic disc within [FORMULA] kpc from the Sun, as suggested by some studies of the abundances in HII regions and B-type stars. The same set of homogeneously derived ionic abundances is also used to test the accuracy of the fractional ionization predicted by available grids of models for photoionized nebulae.

Key words: ISM: H ii regions – ISM: abundances – Galaxy: abundances

* Based on observations made with the Isaac Newton Telescope, operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

© European Southern Observatory (ESO) 1999

Online publication: November 16, 1999

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