Analysis of chemical abundances in planetary nebulae with [WC] central
  stars. I. Line intensities and physical conditions
  (Abridged) Planetary nebulae (PNe) around Wolf-Rayet [WR] central stars
([WR]PNe) constitute a particular photoionized nebula class that represents
about 10% of the PNe with classified central stars. We analyse deep
high-resolution spectrophotometric data of 12 [WR]PNe. This sample represents
the most extensive analysed so far, at such high spectral resolution. We aim to
select the optimal physical conditions in the PNe to be used in ionic abundance
calculations that will be presented in a forthcoming paper. We acquired spectra
at LCO with the 6.5-m telescope and the MIKE spectrograph, covering a
wavelength range from 3350 to 9400 A. The spectra were exposed deep enough to
detect, with signal-to-noise ratio higher than three, the weak ORLs of OII,
CII, and other species. We detect and identify about 2980 emission lines,
which, to date, is the most complete set of spectrophotometric data published
for this type of objects. From our deep data, numerous diagnostic line ratios
for Te and Ne are determined from CELs, ORLs, and continuum measurements.
Densities are closely described by the average of all determined values for
objects with ne<10^4 cm-3, and by ne([Cl III]) for the densest objects. For Te,
we adopt a three-zone ionization scheme, where the low ionization zone is
characterized by Te([NII]), the medium ionization zone by Te([OIII]) and the
highest ionization one by Te([ArIV]) when available. We compute Te from the HI
Paschen discontinuity and from HeI lines. We do not find evidences of the
presence of low-temperature, high-density clumps in our [WR]PNe from the
analysis of faint O II and N II plasma diagnostics. The behaviour of
Te([OIII])/Te([NII]) being very low for high ionization degrees can be
reproduced by a set of combined matter-bounded and radiation-bounded models,
however, for the lowest temperature ratios, too high metallicity seem required.
