The impact of (n, γ) reaction rate uncertainties of unstable isotopes near N = 50 on the i-process nucleosynthesis in He-shell flash white dwarfs

Denissenkov, Pavel; Perdikakis, Georgios; Herwig, Falk; Schatz, Hendrik; Ritter, Christian; Pignatari, Marco; Jones, Samuel; Nikas, Stylianos; Spyrou, Artemis

Abstract

The first-peak s-process elements Rb, Sr, Y and Zr in the post-AGB star Sakurai's object (V4334 Sagittarii) have been proposed to be the result of i-process nucleosynthesis in a post-AGB very-late thermal pulse event. We estimate the nuclear physics uncertainties in the i-process model predictions to determine whether the remaining discrepancies with observations are significant and point to potential issues with the underlying astrophysical model. We find that the dominant source in the nuclear physics uncertainties are predictions of neutron capture rates on unstable neutron rich nuclei, which can have uncertainties of more than a factor 20 in the band of the i-process. We use a Monte Carlo variation of 52 neutron capture rates and a 1D multi-zone post-processing model for the i-process in Sakurai's object to determine the cumulative effect of these uncertainties on the final elemental abundance predictions. We find that the nuclear physics uncertainties are large and comparable to observational errors. Within these uncertainties the model predictions are consistent with observations. A correlation analysis of the results of our MC simulations reveals that the strongest impact on the predicted abundances of Rb, Sr, Y and Zr is made by the uncertainties in the (n, γ) reaction rates of 85Br, 86Br, 87Kr, 88Kr, 89Kr, 89Rb, 89Sr, and 92Sr. This conclusion is supported by a series of multi-zone simulations in which we increased and decreased to their maximum and minimum limits one or two reaction rates per run. We also show that simple and fast one-zone simulations should not be used instead of more realistic multi-zone stellar simulations for nuclear sensitivity and uncertainty studies of convective–reactive processes. Our findings apply more generally to any i-process site with similar neutron exposure, such as rapidly accreting white dwarfs with near-solar metallicities.

Citation

Denissenkov, P., Perdikakis, G., Herwig, F., Schatz, H., Ritter, C., Pignatari, M., Jones, S., Nikas, S., & Spyrou, A. (2018). The impact of (n, γ) reaction rate uncertainties of unstable isotopes near N = 50 on the i-process nucleosynthesis in He-shell flash white dwarfs. Journal of Physics G: Nuclear and Particle Physics, 45(5), 055203. https://doi.org/10.1088/1361-6471/aabb6e

• Journal Article Type: Article
• Acceptance Date: Apr 4, 2018
• Online Publication Date: Apr 16, 2018
• Publication Date: Apr 13, 2018
• Deposit Date: Apr 19, 2018
• Publicly Available Date: Apr 14, 2019
• Journal: Journal of Physics G: Nuclear and Particle Physics
• Print ISSN: 0954-3899
• Publisher: IOP Publishing
• Peer Reviewed: Peer Reviewed
• Volume: 45
• Issue: 5
• Article Number: 055203
• Pages: 055203
• DOI: https://doi.org/10.1088/1361-6471/aabb6e
• Keywords: Nuclear and High Energy Physics
• Public URL: https://hull-repository.worktribe.com/output/793128
• Publisher URL: http://iopscience.iop.org/article/10.1088/1361-6471/aabb6e/meta
• Additional Information: Journal title: Journal of Physics G: Nuclear and Particle Physics; Article type: paper; Article title: The impact of (n, γ) reaction rate uncertainties of unstable isotopes near N = 50 on the i-process nucleosynthesis in He-shell flash white dwarfs; Copyright information: © 2018 IOP Publishing Ltd; Date received: 2017-11-22; Date accepted: 2018-04-04; Online publication date: 2018-04-16
• Contract Date: Apr 25, 2018