Abstract
The abundances of sodium and oxygen are observed to be anti-correlated in all well-studied globular clusters. Asymptotic giant branch (AGB) stars undergoing hot bottom burning (HBB) are thought to be prime candidates for producing sodium-rich oxygen-poor material and expelling it into the cluster ISM. The 22Ne(p,gamma)23Na reaction has been shown to strongly influence the amount of 23Na produced during HBB. This reaction is also important for classical novae nucleosynthesis, with sensitivity studies showing that the abundances of several isotopes in the Ne-Al region are significantly altered when varying the reaction rate between available compilations. Here we present the first inverse kinematics measurements of key resonances strengths as well as the direct capture S-factor. Together, this study represents the largest centre of mass energy range (149-1222 keV) over which this reaction has been measured in a single experiment. Our results for low-energy resonances at Ecm=149, 181 and 248 keV are in good agreement with recent forward kinematics results; we also find a direct capture S-factor consistent with the literature value of 62 keV.b. However, in the case of the important reference resonance at Ecm = 458 keV we find a strength value of wg=0.44 +/- 0.02 eV, which is significantly lower than recent results. Using our new recommended rate we explore the impact of these results on both AGB star and classical novae nucleosynthesis. In the case of AGB stars we see very little abundance changes with respect to the rate included in the STARLIB-2013. However, we observe changes of up to a factor of 2 in isotopes produced in both the carbon-oxygen (CO) and oxygen-neon (ONe) classical novae models considered here. The 22Ne(p,gamma)23Na reaction rate is now sufficiently well constrained to not significantly contribute toward abundance uncertainties from classical novae nucleosynthesis models.
Highlights
Globular clusters (GCs) are dense associations of stars that formed in the early universe
Resonance at Ec.m. = 1222 keV The first absolute 22Ne(p, γ )23Na resonance strength measurement was reported by Keinonen et al [41] for the 1222-keV resonance, with a quoted strength value of ωγ1222 = 10.5 ± 1.0 eV
The strength of the 1222-keV resonance was reported as ωγ1222 = 11.03 ± 1.00 eV, assuming a target thickness derived from a 458-keV resonance strength of ωγ458 = 0.605 ± 0.062 eV Here we report a new absolute yield measurement for the 1222-keV resonance that is determined independently of other resonance strength values
Summary
Globular clusters are known to exhibit anomalous abundance trends such as the sodium-oxygen anticorrelation. Purpose: At temperatures relevant for both HBB in AGB stars and classical nova nucleosynthesis, the 22Ne(p, γ ) 23Na reaction rate is dominated by narrow resonances, with additional contribution from direct capture. Results: For the low-energy resonances, located at center of mass energies of 149, 181, and 248 keV, we recover stength values of ωγ149 = 0.17+−00..0054, ωγ181 = 2.2 ± 0.4, and ωγ248 = 8.2 ± 0.7 μeV, respectively These results are in broad agreement with recent studies performed by the LUNA and TUNL groups. For the important reference resonance at 458 keV we obtain a strength value of ωγ458 = 0.44 ± 0.02 eV, which is significantly lower than recently reported values. We assessed the impact of the present reaction rate in reference to a variety of astrophysical environments, including AGB stars and classical novae. The present rate does impact upon the production of nuclei in the Ne-Al region for classical novae, with dramatically improved uncertainties in the predicted isotopic abundances present in the novae ejecta
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