Echelle spectrophotometry of the 30 Doradus nebula in the LMC is presented. The data consist of VLT UVES observations in the 3100-10350 ? range. The intensities of 366 emission lines have been measured, including 269 identified permitted lines of H0, He0, C0, C+, N+, N++, O0, O+, Ne0, Ne+, S+, S++, Si0, Si+, Si++, Ar+, and Mg+; many of them are produced by recombination only while others mainly by fluorescence. Electron temperatures and densities have been determined using different line intensity ratios. The He+, C++, O+, and O++ ionic abundances have been derived from recombination lines; these abundances are almost independent of the temperature structure of the nebula. Alternatively, abundances from collisionally excited lines have been derived for a large number of ions of different elements; these abundances depend strongly on the temperature structure. Accurate t2 values have been derived from the Balmer continuum and by comparing the C++, O+, and O++ ionic abundances obtained from collisionally excited and recombination lines. The chemical composition of 30 Doradus is compared with those of Galactic and extragalactic H II regions. The values of ΔY/ΔO, ΔY/ΔZ, and Yp are also discussed.
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