Recombination line abundances in the winds of the [WC] Wolf-Rayet stars

Abstract

We present a preliminary abundance analysis, utilising recombination theory, for the [WC] Wolf-Rayet central stars of the planetary nebulae NGC 6751 and NGC 6905. This analysis is based on optical spectrophotometry of a sample of [WC] stars which show a strong O vi 3811, 34 å feature in emission. We have performed a recombination line analysis of stellar wind emission lines which are judged to be optically thin, in order to derive relative C, O and He abundances. We also present a comparison of the derived wind abundances with those of Population I WO stars. For the [WC 4] central star of NGC 6751, we have derived C/He = 0.35 and C/O = 4.2, by number. And for the [WC 3] central star of NGC 6905, we have derived C/He = 0.36 and C/O< 12. These surface abundances are comparable to the abundances that have been derived for early type [WC] stars via more complex NLTE modelling (e.g. Koesterke & Hamann 1996).