Confirmation of a new resonance in Si26 and contribution of classical novae to the galactic abundance of Al26

The Al25(p,γ) reaction has long been highlighted as a possible means to bypass the production of Al26 cosmic γ rays in classical nova explosions. However, uncertainties in the properties of key resonant states in Si26 have hindered our ability to accurately model the influence of this reaction in such environments. We report on a detailed γ-ray spectroscopy study of Si26 and present evidence for the existence of a new, likely ℓ=1, resonance in the Al25 + p system at Er=153.9(15) keV. This state is now expected to provide the dominant contribution to the Al25(p,γ) stellar reaction rate over the temperature range, T≈0.1−0.2 GK. Despite a significant increase in the rate at low temperatures, we find that the final ejected abundance of Al26 from classical novae remains largely unaffected even if the reaction rate is artificially increased by a factor of 10. Based on new, galactic chemical evolution calculations, we estimate that the maximum contribution of novae to the observed galactic abundance of Al26 is ≈0.2M⊙. Finally, we briefly highlight the important role that super-asymptotic giant branch stars may play in the production of Al26.Received 8 September 2022Revised 2 June 2023Accepted 18 August 2023DOI:https://doi.org/10.1103/PhysRevC.108.035807Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNuclear astrophysicsNucleosynthesis in explosive environmentsProperties20 ≤ A ≤ 38TechniquesRadiation detectorsSpectrometers & spectroscopic techniquesNuclear Physics