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Preprint 13/04

Fluorine in extremely hot post-AGB stars: evidence for nucleosynthesis

K. Werner (1), T. Rauch (1,2) and J.W. Kruk (3)

(1) Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
(2) Dr.-Remeis-Sternwarte, Universität Erlangen-Nürnberg, Sternwartstraße 7, 96049 Bamberg, Germany
(3) Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, U.S.A.

A&A 433, 641 (2005)

Abstract. We have discovered lines of highly ionized fluorine F V and F VI in the far-UV spectra of extremely hot (T_eff=85000 -150000 K) post-AGB stars. Our sample comprises H-rich central stars of planetary nebulae as well as H-deficient PG1159 stars. We performed non-LTE calculations and find strong F overabundances (up to 10^-4 by mass, i.e., 250 times solar) in a number of PG1159 stars, while F is essentially solar in the H-rich stars. Since PG1159 stars are believed to exhibit intershell matter of the preceding AGB phase on their surface, their chemical analyses allow for a direct insight into nucleosynthesis processes during the AGB phase. The high F abundances in PG1159 stars confirm the conclusion from abundance determinations in giants, that F is synthesized in AGB stars and that the F enrichment in the intershell must be very high.
 
Key words: stars: abundances - stars: atmospheres - stars: evolution - stars: AGB and post-AGB - stars: white dwarfs

Preprint (153 kb PDF file including figures)
Astrophysics (astro-ph): astro-ph/0412258

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