TY - JOUR A1 - Pena, M. A1 - Stastinska, G. A1 - Esteban, C. A1 - Koesterke, Lars A1 - Medina, S. A1 - Kingsburgh, R. T1 - Galactic planetary nebulae with Wolf-Rayet nuclei : I. Objects with [WC]-early type stars Y1 - 1998 ER - TY - JOUR A1 - Pena, M. A1 - Stastinska, G. A1 - Esteban, C. A1 - Koesterke, Lars A1 - Medina, S. A1 - Kingsburgh, R. T1 - Spectroscopy of planetary nebulae with [WR] nuclei Y1 - 1999 ER - TY - JOUR A1 - Mesa-Delgado, A. A1 - Esteban, C. A1 - García-Rojas, J. T1 - Ring Nebulae BT - Tracers of the CNO Nucleosynthesis JF - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015 N2 - Preliminary results are presented from spectroscopic data in the optical range of the Galactic ring nebulae NGC 6888, G2:4+1:4, RCW 58 and Sh2-308. Deep observations with long exposure times were carried out at the 6.5m Clay Telescope and at the 10.4m Gran Telescopio Canarias. In NGC 6888, recombination lines of C ii, O ii and N ii are detected with signal-to-noise ratios higher than 8. The chemical content of NGC 6888 is discussed within the chemical enrichment predicted by evolution models of massive stars. For all nebulae, a forthcoming work will content in-depth details about observations, analysis and final results (Esteban et al. 2015, in prep.). Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88299 SP - 325 EP - 328 ER -