Chemical Abundances of the Galactic H ii Region NGC 3576 Derived from Very Large Telescope Echelle Spectrophotometry

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 H 0 , He 0 , C + , N 0 , N + , N ++ , O 0 , O + , Ne + , S ++ , Si 0 , Si + , Ar 0 , 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 t 2 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.