Physical Conditions of the Planetary Nebula NGC 5315 Derived from VLT Echelle Observations and the t 2 Problem

Abstract

Echelle spectrophotometry of the planetary nebula NGC 5315 is presented. The data consist of VLT UVES observations in the 3100-10450 ? range. The intensities of 556 emission lines have been measured, including 508 identified permitted lines of H0, He0, C0, C+, N0, N+, N++, O0, O+, Ne0, Ne+, Mg+, Si+, S0, S+, S++, and Ar+. Electron temperatures and densities have been determined using many different line intensity ratios. The He+, C++, N++, O++, and Ne++ 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 He I lines, and by comparing the O++ ionic abundances obtained from collisionally excited and recombination lines. The similarity between the widths and radial velocities of the O II and the [O III] lines rules out the presence of chemical abundance inhomogeneities in this object. The chemical composition of NGC 5315 is compared with those of the Orion nebula and the Sun.