Electron temperatures and free-electron energy distributions of nebulae from C ii dielectronic recombination lines

A recently generated theoretical line list of C ii dielectronic recombination lines together with observational data gathered from the literature is used to investigate the electron temperature in a range of astronomical objects, mainly planetary nebulae. The electron temperature is obtained by a least-squares optimization using all the reliable observed lines in each object. In addition, the subset of lines arising directly from autoionizing states is used to directly determine the free-electron energy distribution which is then compared with various theoretical possibilities. The method described here can potentially determine whether there are departures from Maxwell-Boltzmann distributions in some nebulae, as has been recently proposed. Using published observations of the three planetary nebulae where the relevant lines are recorded, we find that the data are best matched by Maxwell-Boltzmann distributions but that the uncertainties are sufficiently large at present that κ-distributions or two-component nebular models are not excluded.