On the neon abundance in PG 1159-type central stars on planetary nebulae.

Abstract

We announce the first detection and identification of a neon line in the spectra of hot central stars of planetary nebulae. It concerns the 3644A absorption line of highly ionised neon (Ne VII) in the extremely hot (T_eff_ > 100000 K) PG1159-type (i.e. hydrogen deficient) objects RXJ2117+3412, NGC246, and K 1-16. We present medium resolution spectra and a non-LTE analysis aiming at the abundance determination of neon in these exotic stars. The analysis reveals that the neon mass fraction (about 2%) strongly exceeds the solar value. This is in accordance with our understanding of the evolutionary status of the PG 1159 stars: they exhibit deep intershell matter, which was processed by triple alpha burning and layed bare after strong mass-loss events.