Analysis of chemical abundances in planetary nebulae with [WC] central stars. II. Chemical abundances and the abundance discrepancy factor

摘要

(Abridged) We present the abundance analysis of 12 PNe ionized by [WC]-typestars and wels obtained from high-resolution spectrophotometric data. Our mainaims are to determine the chemical composition of the PNe and to study thebehaviour of the abundance discrepancy problem (ADF) in this type of planetarynebulae. The detection of a large number of optical recombination lines (ORLs)and collisionally excited lines (CELs) from different ions were presentedpreviously. Most of the ORLs were reported for the first time in these PNe.Ionic abundances were derived from the available CELs and ORLs, usingpreviously determined physical conditions. Based on these two sets of ionicabundances, we derived the total chemical abundances in the nebulae usingsuitable ICFs (when available). In spite of the [WC] nature of the centralstars, moderate ADF(O^++), in the range from 1.2 to 4, were found for all theobjects. We found that when the quality of the spectra is high enough the ORLsO^++/H^+ abundance ratios obtained from different multiplets excited mainly byrecombination are very similar. Possible dependence of ADFs with some nebularcharacteristics were analysed, finding no correlation. Abundances derived fromCELs were corrected by determining the t^2 parameter. O abundances for PNe,derived from ORLs, are in general larger than the solar abundance. We derivedthe C/O ratio from ORLs and N/O and alpha-element/O ratios from CELs and foundthat these PNe are, in average, N-and C-richer than the average of large PNsamples. About half of our sample is C-rich (C/O>1). The alpha-elements grow inlockstep with O abundance. Comparing the N/O and C /O ratios with those derivedfrom stellar evolution models, we estimate that about half of our PNe haveprogenitors with initial masses > 4 M_sun. No correlation was found between thestellar [WC]-type and the nebular abundances.