Nebular and interstellar absorption lines in planetary nebulae : the case of NGC 6543.

Abstract

Using high resolution IUE spectra it is possible to separate the narrow absorption lines due to the interstellar material and the nebular matter. The analysis of nebular absorption lines has three advantages. First the column densities of ions different from those observed in emission can be determined. The abundance of the elements are then readily derived without applying ionization correction. Second the population ratio of the fine structure levels and the ground level of certain ions and the ionization balance can yield an independent estimate of the electron density. Third using Lyman α absorption and interstellar measurements of S and Zn in the foreground extinction can be estimated. The authors use the above method for NGC 6543. They derive the abundance of C, Si, S and Al.