Post-AGB stars as testbeds of nucleosynthesis in AGB stars

Abstract

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 Teff, 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 (M* < 0.56 Msun); 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.

arXiv comment17 pages including 9 figures and 2 tables, accepted in Astronomy and Astrophysics

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• HST Snapshot Survey of Post-AGB Objects
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• First detection of surface magnetic fields in Post-AGB stars : the cases of U Monocerotis and R Scuti
• AGB nucleosynthesis in the Large Magellanic Cloud. Detailed abundance analysis of the RV Tauri star MACHO47.2496.8
• The color dependent morphology of the post-AGB star HD161796
• The problematically short superwind of OH/IR stars - Probing the outflow with the 69 μm spectral band of forsterite
• Infrared Spectroscopic Study of a Selection of AGB and Post-AGB Stars
• Observed relationship between CO2-1 and dust emission during post-AGB phase
• Evolutionary stage of the spectral variable BD+48 1220=IRAS 05040+4820
• High-resolution spectroscopy of the high velocity hot post-AGB star IRAS 18379-1707 (LS 5112)