Issue |
A&A
Volume 467, Number 3, June I 2007
|
|
---|---|---|
Page(s) | 1139 - 1146 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20066842 | |
Published online | 13 March 2007 |
Can the third dredge-up extinguish hot-bottom burning in massive AGB stars?
Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 3, 35122 Padova, Italia e-mail: paola.marigo@unipd.it
Received:
29
November
2006
Accepted:
1
February
2007
The crucial importance of molecular opacities in modelling the evolution of AGB stars at varying surface C/O ratio has been highlighted in Marigo (2002).
The inadequacy of solar-scaled opacities when applied to models of carbon stars has been
shown, and hence the need for correctly coupling the molecular opacities to the current surface
chemical composition of AGB stars. The aim of the present follow-up study is
to investigate the effects of variable molecular opacities
on the evolutionary properties of luminous AGB stars with massive envelopes, i.e. with initial masses from ≈3.5 to 5-8
, which are predicted to experience both the third dredge-up and hot-bottom burning. It is found that if the dredge-up of carbon is efficient enough to lead to an early transition from C/O < 1 to C/O > 1, then
hot-bottom burning may be weakened, extinguished, or even prevented.
The physical conditions for this occurrence are analysed and a few
theoretical and observational implications are discussed.
Importantly, it is found that the inclusion of variable molecular
opacities could significantly change the current predictions for the chemical
yields contributed by intermediate-mass AGB stars, with M
3.5-4.0
, that make as much as ~30-50% of all stars expected to undergo hot-bottom burning.
Key words: stars: abundances / stars: AGB and post-AGB / stars: carbon / stars: evolution / stars: general / stars: late-type
© ESO, 2007
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