Abundances of Planetary Nebulae BD+30 3639 and NGC 6543 J. Bernard-Salas, S. R. Pottasch, P. R. Wesselius and W. A. Feibelman A&A, 406 1 (2003) 165-174 Published online: 17 November 2003 DOI: 10.1051/0004-6361:20030777