Jorge García-Rojas (Instituto de Astrofísica de Canarias, Spain)
I will present the analysis of very deep echelle spectra of a dozen planetary nebulae with [WC] or weak emission lines (wels) central stars. Physical conditions (electron density and temperature) are derived from several diagnostics, and ionic chemical abundances, including oxygen, are determined from both, strong collisionally excited lines (CELs) and from faint optical recombination lines (ORLs). Tens of O II ORLs from several multiplets have been isolated and measured giving consistent results among different multiplets. O I ORLS are measured with a reasonable accuracy in several objects. The computed abundance discrepancy factors (ADFs) for both O+ and O++ are moderate, with values around or lower than 4. I will discuss the importance of using appropriate diagnostics to derive physical conditions (both electron density and temperature) to properly compute the abundances from CELs ions of oxygen and that ORLs, with the available atomic data, are virtually unaffected by uncertainties in the adopted physical conditions.