Abstract
About 50 PNe in our Galaxy are known to have central stars of the carbon sequence Wolf-Rayet ([WC]) type stars and their atmospheres are almost pure helium and carbon. It has been suggested that the spectral sequence of [WC] stars and the ``weak emission line stars'' (WELS, as defined by Tylenda et al. 1993) corresponds to the following evolutionary sequence: late-[WC] -> early-[WC] -> WELS -> PG 1159 type stars. This suggestion is based upon both the analysis of the stellar atmospheres and the nebular properties of the planetary nebulae around [WC] stars (WRPNe) (e.g., Parthasarathy et al. 1998). This suggestion is controversial (Gorny & Tylenda 2000; Peña et al. 2001) and in order to study the nature and evolution of WRPNe and WELS, we have obtained a homogeneous high spectral resolution (echelle) data set of 30 planetary nebulae and their nuclei using the 2.1-m telescope at the Observatorio Astronómico Nacional, San Pedro Mártir, México.
