New Constraints on Sodium Production in Globular Clusters From the 23Na(3He, d)24Mg Reaction

Abstract

Globular clusters consist of hundreds of thousands of stars gravitationally bound in a relatively small radius. Over the last few decades, intense observational study has revealed that globular clusters are comprised of multiple stellar populations each with distinct chemical signatures. The star-to-star Na-O anticorrelation is the most pervasive of these so called abundance anomalies, and is theorized to be the result of stellar material undergoing hydrogen burning at 50-100 MK. Unfortunately, many thermonuclear reaction rates suffer from large uncertainties at these temperatures, thereby limiting our understanding of nucleosynthesis in globular clusters. One of the most critical rates is the sodium destroying reaction 23Na(p, γ)24Mg, which is dominated at these temperatures by direct capture and a single, narrow resonance at Er ≈ 138 keV. Using the Enge Split-pole Spectrograph at Triangle Universities Nuclear Laboratory (TUNL), we have measured the transfer reaction, 23Na(3He, d)24Mg. Excited states in the astrophysical region of interest were observed, including the state corresponding to the 138 keV resonance. This measurement finds a dramatically lower resonance energy than previously reported for this resonance. Further analysis making use of newly developed techniques that incorporate the distorted wave Born approximation into a Bayesian model, made it possible to assign probabilities to each ℓ value and to extract spectroscopic factors with statistically rigorous uncertainties. These results indicate the 23Na(p, γ) reaction rate is five times higher than previously reported, a significant implication for the destruction of sodium in stellar material. Download AbstractPresentation Slides