Impact of a revised 25Mg(p, γ)26Al reaction rate on the operation of the Mg-Al cycle

Proton captures on Mg isotopes play an important role in the Mg-Al cycle active in stellar H-burning regions. In particular, the low-energy resonances with E < 200 keV in the 25Mg(p,γ)26Al reaction affect the production of radioactive 26Algs as well as the resulting Mg/Al abundance ratio. Reliable estimations of these quantities require precise measurements of the strengths of these low-energy resonances. On the base of a new experimental study performed at LUNA, we provide revised rates of the 25Mg(p,γ)26Algs and the 25Mg(p,γ)26Alm reactions. In the temperature range 50 to 150 MK, the new recommended rate of the 26Al production is up to 5 times higher than previously assumed. In addition, at T= 100 MK, the revised total reaction rate is a factor of 2 higher. The effects of this significant revision of the Mg-Al cycle are discussed. In particular, due to the large increase of the 25Mg(p,γ)26Alm rate, the production of 26Al in H-burning regions is less efficient than previously obtained. As a result, the new rates should imply a smaller contribution from Wolf-Rayet stars to the galactic 26Al budget. Similarly, within the estimated uncertainties, the AGB extra-mixing scenario does not appear a definite solution for the problem of the O-rich presolar grains showing extremely large values of 26Al/27Al ratio (i.e. > 10−2. Finally, thanks to the substantial increase of the total reaction rate, the self-pollution scenario for Globular Clusters may produce a more robust explanation for the observed Mg-Al anticorrelation.