The WC10 central stars CPD-56 deg8032 and He2-113 -III. Wind electron temperatures and abundances

We present a direct spectroscopic measurement of the wind electron temperatures and a determination of the stellar wind abundances of the WC10 central stars of planetary nebulae CPD-56 deg8032 and He2-113, for which high-resolution (0.15-A) UCLES echelle spectra have been obtained using the 3.9-m Anglo-Australian Telescope. The intensities of dielectronic recombination lines, originating from autoionizing resonance states situated in the C^2++e^- continuum, are sensitive to the electron temperature through the populations of these states, which are close to their LTE values. The high-resolution spectra allow the intensities of fine-structure components of the dielectronic multiplets to be measured. New atomic data for the autoionization and radiative transition probabilities of the resonance states are presented, and used to derive wind electron temperatures in the two stars of 21300K for CPD-56 deg8032 and 16400K for He2-113. One of the dielectronic lines is shown to have an autoionization width in agreement with the theoretical predictions. Wind abundances of carbon with respect to helium are determined from bound-bound recombination lines, and are found to be C/He=0.44 for CPD-56 deg8032 and C/He=0.29 for He2-113 (by number). The oxygen abundances are determined to be O/He=0.24 for CPD-56 deg8032 and 0.26 for He2-113. The effect of optical depth on the temperature and abundance determinations is investigated by means of a Sobolev escape-probability model. We conclude that the optically thicker recombination lines can still be used for abundance determinations, provided that their upper levels are far from LTE.