Chemical abundances in seven galactic planetary nebulae

Laboratório de Análise Numérica e Astrofísica, Departamento de Matemática, Universidade Federal de Santa Maria, 97119-900 Santa Maria, RS, Brazil e-mail: angela@lana.ccne.ufsm.br

Received: 27 August 2005
Accepted: 1 December 2005

Abstract

An observational study of chemical abundances in the galactic planetary nebulae NGC 1535, NGC 2438, NGC 2440, NGC 3132, NGC 3242, NGC 6302, and NGC 7009 based on long-slit spectra of high signal-to-noise ratio in the 3100 to 6900 Å range is presented. We determined the N, O, Ne, S, and Cl abundances from collisionally excited lines and the He and abundances from recombination lines. The estimates derived from recombination lines are about a factor of four and two higher than those derived from forbidden lines for NGC 7009 and NGC 3242, respectively. Spatial profiles of abundance from permitted lines and from forbidden lines were obtained for the planetary nebula NGC 7009. The differences between derived from recombination and from forbidden lines present smooth variations along the nebular surface of NGC 7009, with the differences decreasing from the center to the edges of the nebula. If these abundance differences are explained by the presence of electron temperature fluctuations, quantified by the parameter t², a value of about is required for NGC 3242 and NGC 7009.