2004ApJS..153..501G

We present echelle spectrophotometry of the Galactic H II region NGC 3576. The data have been taken with the VLT UVES echelle spectrograph in the 3100-10400 Å range. We have measured the intensities of 458 emission lines, 344 are permitted lines of H⁰, He⁰, C⁺, N⁰, N⁺, N⁺⁺, O⁰, O⁺, Ne⁺, S⁺⁺, Si⁰, Si⁺, Ar⁰, and Ar⁺; some of them are produced by recombination and others mainly by fluorescence. Electron temperatures and densities have been determined using different continuum and line intensity ratios. We have derived He⁺, C⁺⁺, O⁺, O⁺⁺, and Ne⁺⁺ ionic abundances from pure recombination lines. We have also derived abundances from collisionally excited lines for a large number of ions of different elements. Remarkably consistent estimations of t² have been obtained by comparing Balmer and Paschen with [O III] temperatures, and O⁺⁺ and Ne⁺⁺ ionic abundances obtained from collisionally excited and recombination lines. The chemical composition of NGC 3576 is compared with those of other Galactic H II regions and with the one from the Sun. A first approach to the gas-phase Galactic radial abundance gradient of C as well as of the C/O ratio has been made.