Post-AGB stars as testbeds of nucleosynthesis in AGB starsG. Stasinska1, R. Szczerba2, M. Schmidt2 and N. Siódmiak2
1 LUTH, Observatoire de Meudon, 5 Place Jules Janssen, 92195 Meudon Cedex, France
2 N. Copernicus Astronomical Center, Rabianska 8, 87-100 Torun, Poland
(Received 2 June 2005 / Accepted 30 December 2005 )
We construct a data base of 125 post-AGB objects (including R CrB and extreme helium stars) with published photospheric parameters (effective temperature and gravity) and chemical composition. We estimate the masses of the post-AGB stars by comparing their position in the (log , log g) plane with theoretical evolutionary tracks of different masses. We construct various diagrams, with the aim of finding clues to AGB nucleosynthesis. This is the first time that a large sample of post-AGB stars has been used in a systematic way for such a purpose and we argue that, in several respects, post-AGB stars should be more powerful than planetary nebulae to test AGB nucleosynthesis. Our main findings are that: the vast majority of objects which do not show evidence of N production from primary C have a low stellar mass ( ); there is no evidence that objects which did not experience 3rd dredge-up have a different stellar mass distribution than objects that did; there is clear evidence that 3rd dredge-up is more efficient at low metallicity. The sample of known post-AGB stars is likely to increase significantly in the near future thanks to the ASTRO-F and follow-up observations, making these objects even more promising as testbeds for AGB nucleosynthesis.
Key words: stars: AGB and post AGB -- stars: abundances -- stars: evolution -- nuclear reactions, nucleosynthesis, abundances
© ESO 2006