In massive stars (initial mass of ≳9 M⊙), the weak s- (slow neutron capture) process produces elements between Fe and Zr, enriching the Galaxy with these elements through core-collapse supernova explosions. The weak s-process nucleosynthesis is driven by neutrons produced in the 22Ne(α, n)25Mg reaction during convective He core and C shell burning. The yields of heavy elements thus depend on the 22Ne(α, n)25Mg and the competitive 22Ne(α, γ)26Mg reaction rates, which are dominated by several narrow-resonance reactions. While the accuracy of these rates has been under debate for decades, recent experimental efforts, including ours, drastically reduced these uncertainties. In this work, we use a set of 280 massive star nucleosynthesis models calculated using different 22Ne(α, n)25Mg and 22Ne(α, γ)26Mg rates and a galactic chemical evolution (GCE) study to probe their impact on the weak s-process elemental abundances in the Galaxy. The GCE was computed with the OMEGA+ code, using the new sets of stellar yields with different 22Ne+α rates. From GCE, we find that these rates are causing up to 0.45 dex of variations in the [Cu/Fe], [Ga/Fe], and [Ge/Fe] ratios predicted at solar metallicity. The greatest impact on the stellar nucleosynthesis and GCE results derives from uncertainties in the (α, n) strength (ωγ(α,n)) of the Ex = 11.32 MeV resonance. We show that variations observed in the GCE calculations for weak s-process elements become negligibly smaller than dispersions found in observations once the ωγ(α,n) is accurately determined within the uncertainty of 10%–20% (typically reported experimental errors for the resonance) in future nuclear physics experiments.
Kotar, Emma, et al. "Impact of the Latest <sup>22</sup>Ne+<em>α</em> Reaction Rates on Nucleosynthesis in Massive Stars and Galactic Chemical Evolution." The Astrophysical Journal, vol. 994, no. 2, Nov. 2025. https://doi.org/10.3847/1538-4357/ae0ad3
Kotar, Emma, Ota, Shuya, Dewey, Allyson, Millman, Joshua, Roberti, Lorenzo, & Pignatari, Marco (2025). Impact of the Latest <sup>22</sup>Ne+<em>α</em> Reaction Rates on Nucleosynthesis in Massive Stars and Galactic Chemical Evolution. The Astrophysical Journal, 994(2). https://doi.org/10.3847/1538-4357/ae0ad3
Kotar, Emma, Ota, Shuya, Dewey, Allyson, et al., "Impact of the Latest <sup>22</sup>Ne+<em>α</em> Reaction Rates on Nucleosynthesis in Massive Stars and Galactic Chemical Evolution," The Astrophysical Journal 994, no. 2 (2025), https://doi.org/10.3847/1538-4357/ae0ad3
@article{osti_3010976,
author = {Kotar, Emma and Ota, Shuya and Dewey, Allyson and Millman, Joshua and Roberti, Lorenzo and Pignatari, Marco},
title = {Impact of the Latest <sup>22</sup>Ne+<em>α</em> Reaction Rates on Nucleosynthesis in Massive Stars and Galactic Chemical Evolution},
annote = {In massive stars (initial mass of ≳9 M⊙), the weak s- (slow neutron capture) process produces elements between Fe and Zr, enriching the Galaxy with these elements through core-collapse supernova explosions. The weak s-process nucleosynthesis is driven by neutrons produced in the 22Ne(α, n)25Mg reaction during convective He core and C shell burning. The yields of heavy elements thus depend on the 22Ne(α, n)25Mg and the competitive 22Ne(α, γ)26Mg reaction rates, which are dominated by several narrow-resonance reactions. While the accuracy of these rates has been under debate for decades, recent experimental efforts, including ours, drastically reduced these uncertainties. In this work, we use a set of 280 massive star nucleosynthesis models calculated using different 22Ne(α, n)25Mg and 22Ne(α, γ)26Mg rates and a galactic chemical evolution (GCE) study to probe their impact on the weak s-process elemental abundances in the Galaxy. The GCE was computed with the OMEGA+ code, using the new sets of stellar yields with different 22Ne+α rates. From GCE, we find that these rates are causing up to 0.45 dex of variations in the [Cu/Fe], [Ga/Fe], and [Ge/Fe] ratios predicted at solar metallicity. The greatest impact on the stellar nucleosynthesis and GCE results derives from uncertainties in the (α, n) strength (ωγ(α,n)) of the Ex = 11.32 MeV resonance. We show that variations observed in the GCE calculations for weak s-process elements become negligibly smaller than dispersions found in observations once the ωγ(α,n) is accurately determined within the uncertainty of 10%–20% (typically reported experimental errors for the resonance) in future nuclear physics experiments.},
doi = {10.3847/1538-4357/ae0ad3},
url = {https://www.osti.gov/biblio/3010976},
journal = {The Astrophysical Journal},
issn = {ISSN 1538-4357},
number = {2},
volume = {994},
place = {United States},
publisher = {IOP Publishing},
year = {2025},
month = {11}}
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Organization:
National Science Foundation (NSF); USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Nuclear Physics (NP); USDOE Office of Science (SC), Office of Workforce Development for Teachers & Scientists (WDTS)
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 812https://doi.org/10.1016/j.nima.2015.12.034