Re-evaluation of the ${}^{22}$Ne($\alpha ,\gamma$)${}^{26}$Mg and ${}^{22}$Ne($\alpha ,n$)${}^{25}$Mg reaction rates

Abstract

The competing ${}^{22}$Ne($\alpha ,\gamma$)${}^{26}$Mg and ${}^{22}$Ne($\alpha ,n$)${}^{25}$Mg reactions control the production of neutrons for the weak $s$-process in massive and AGB stars. In both systems, the ratio between the corresponding reaction rates strongly impacts the total neutron budget and strongly influences the final nucleosynthesis. The ${}^{22}$Ne($\alpha ,\gamma$)${}^{26}$Mg and ${}^{22}$Ne($\alpha ,n$)${}^{25}$Mg reaction rates was re-evaluated by using newly available information on ${}^{26}$Mg given by various recent experimental studies. Evaluations of The evaluated ${}^{22}$Ne($\alpha ,\gamma$)${}^{26}$Mg reaction rate remains substantially similar to that of Longland {\it et al.} but, including recent results from Texas A\&M, the ${}^{22}$Ne($\alpha ,n$)${}^{25}$Mg reaction rate is lower at a range of astrophysically important temperatures. Stellar models computed with NEWTON and MESA predict decreased production of the weak branch $s$-process due to the decreased efficiency of ${}^{22}$Ne as a neutron source. Using the new reaction rates in the MESA model results in ${}^{96}$Zr/${}^{94}$Zr and ${}^{135}$Ba/${}^{136}$Ba ratios in much better agreement with the measured ratios from presolar SiC grains.

Comments: 23 pages, 15 figures, updated