Identification of neon in FUSE and VLT spectra of extremely hot hydrogen-deficient (pre-) white dwarfs

Abstract

One of the strongest absorption lines observed in far-ultraviolet FUSE spectra of many PG 1159 stars remained unidentified up to now. We show that this line, located at 973.3 Å, stems from . We also present new optical high-resolution spectra of PG 1159 stars, obtained with the ESO VLT, which cover the 3644 Å line and a newly identified multiplet in the 3850–3910 Å region. We compare the observed neon lines with NLTE models and conclude a substantial neon overabundance in a number of objects. Although a detailed analysis is still to be performed in order to compare quantitatively the abundances with evolutionary theory predictions, this corroborates the idea that the PG 1159 stars and their immediate progenitors, the [WC]-type nuclei of planetary nebulae, display intershell matter of their precursor AGB stars. Possibly as the consequence of a late He-shell flash, H-deficient and (s-processed) Fe-depleted matter, that is strongly enriched by 3α-processed elements (C, O, Ne), is dredged up to the surface. Hence, a detailed study of the element abundance patterns in these peculiar stars gives the unique possibility to probe mixing and nucleosynthesis processes in the precursor AGB stars.