Fluorine in extremely hot post-AGB stars: Evidence for nucleosynthesis
Abstract
We have discovered lines of highly ionized fluorine (ion{F}{v} and ion{F}{vi}) in the far-UV spectra of extremely hot (T_eff = 85 000-150 000 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.
Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE is operated for NASA by the Johns Hopkins University under NASA contract NAS5-32985.- Publication:
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Astronomy and Astrophysics
- Pub Date:
- April 2005
- DOI:
- 10.1051/0004-6361:20042258
- Bibcode:
- 2005A&A...433..641W
- Keywords:
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- stars: abundances;
- stars: evolution;
- stars: AGB and post-AGB;
- stars: white dwarfs