Reaction rate uncertainties and the operation of the NeNa and MgAl chains during HBB in intermediate-mass AGB stars

Robert George Izzard, Maria Anna Lugaro, Amanda Irene Karakas, Christian Iliadis, Mark van Raai

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Context. We test the effect of proton-capture reaction rate uncertainties on the abundances of the Ne, Na, Mg and Al isotopes processed by the NeNa and MgAl chains during hot bottom burning (HBB) in asymptotic giant branch (AGB) stars of intermediate mass between 4 and 6 M-circle dot and metallicities between Z = 0.0001 and 0.02. Aims. We provide uncertainty ranges for the AGB stellar yields, for inclusion in galactic chemical evolution models, and indicate which reaction rates are most important and should be better determined. Methods. We use a fast synthetic algorithm based on detailed AGB models. We run a large number of stellar models, varying one reaction per time for a very fine grid of values, as well as all reactions simultaneously. Results. We show that there are uncertainties in the yields of all the Ne, Na, Mg and Al isotopes due to uncertain proton-capture reaction rates. The most uncertain yields are those of Al-26 and Na-23 (variations of two orders of magnitude), Mg-24 and Al-27 ( variations of more than one order of magnitude), Ne-20 and Ne-22 (variations between factors 2 and 7). In order to obtain more reliable Ne, Na, Mg and Al yields from IM-AGB stars the rates that require more accurate determination are: Ne-22( p,.) 23Na, 23Na( p,gamma) Mg-24, Mg-25(p,gamma)Al-26, Mg-26(p,gamma)Al-27 and Al-26(p,gamma)Si-27. Conclusions. Detailed galactic chemical evolution models should be constructed to address the impact of our uncertainty ranges on the observational constraints related to HBB nucleosynthesis, such as globular cluster chemical anomalies.
Original languageEnglish
Pages (from-to)641 - 648
Number of pages8
JournalAstronomy & Astrophysics
Issue number2
Publication statusPublished - 2007
Externally publishedYes

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