COSAM News Articles 2024 02 Collaborative Research: Electron Impact Ionization and Recombination Properties of Heavy Elements Produced by Neutron Star Mergers

Collaborative Research: Electron Impact Ionization and Recombination Properties of Heavy Elements Produced by Neutron Star Mergers

Published: 02/09/2024

Auburn University and University of Georgia
Stuart Loch (PI), Steve Bromley (co-PI), Michael Fogle (co-PI), Phillip Stancil (co-PI)


Electron-impact ionization (EII) and dielectronic recombination (DR) are key electron-impact processes which can dominate the ionization balance in astrophysical plasmas. In kilonovae, the electromagnetic transient following the mergers of neutron stars, the ionization balance in the non-LTE evolutionary stage is dominated by electron-impact processes. State-of-the-art non-LTE models of kilonovae are currently limited by the use of largely approximate data, and accurate cross section data are desperately needed to advance an understanding of the emission of heavy, r-process elements in this non-LTE regime. With improved data, non-LTE analyses can provide unique constraints on the formation sites of the heaviest elements in our universe. The new cross section data generated in this project will have a large impact on data calculation for heavy elements and the application of non-LTE models with these elements.


Intellectual Merit

The proposed project will use modern electronic structure code suites, namely AUTOSTRUCTURE, the Flexible Atomic Code (FAC), and the DARC R-matrix codes to calculate EII and DR cross section data for ions of important r-process elements. Large-scale DR calculations with the Breit-Pauli AUTOSTRUCTURE code will provide DR rate coefficients for temperatures consistent with the thermal (low-energy) and non-thermal (high energy) electron components in kilonovae ejecta. The EII data will be computed with the FAC, and will allow us to investigate the contributions of other ionization mechanisms, such as excitation-autoionization and inner-shell ionization, both of which are not presently included in non-LTE models of kilonovae. By comparisons with a small number of targeted R-matrix calculations with the DARC codes, we will benchmark the EII and DR calculations. These proposed R-matrix calculations will also provide feedback on the applicability of the Distorted Wave formalism employed by AUTOSTRUCTURE and the FAC to calculate the DR and EII data for the heavy, near-neutral systems of interest.


Broader Impacts

The proposed project will provide training and allow both graduate students and early career scientists at multiple institutions to gain expertise in performing these modern, electronic structure/collision calculations. Through interactions with collaborators in the atomic and astrophysics communities, the participants will foster connections and collaborations in their careers. As a part of the project, two participants will be supported each project year to attend the Auburn University Summer Science Institute (SSI). The Auburn SSI brings approximately 20 high-aptitude high school seniors to campus for a week-long exposure to STEM disciplines and research activities. A module for Auburn’s Summer Science Institute, targeted at high school students, will be developed. A freshman seminar on the topic of neutron star mergers will be developed for UGA’s First Year Odyssey Program, while undergraduate students will be recruited from UGA’s Center for Undergraduate Research Opportunities.


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