Speaker
Description
With the recent detection of multiple neutron-star merger events, the need for a more comprehensive understanding of nuclear and atomic properties, as well as advanced astrophysical simulations, has become increasingly important to accurately predict r-process nucleosynthesis yields and electromagnetic signals when presented with observational data. The lack of atomic data has led to a number of computations of weakly ionised r-process opacities, primarily focusing on lanthanides, being published in recent years. However, if the merging process results in the ejection of material with an electron fraction (Ye) of 0.15 or less, nucleosynthesis should progress to actinides. These elements are expected to have photon opacities comparable to, if not greater than, lanthanides [1,2].
Despite our current understanding, large discrepancies can still be found in the opacities related to the uncertainty of atomic data produced using different methodologies. Having accurate atomic data is crucial for the interpretation of observed spectra. [3] To address this issue, we developed an optimisation technique that produces atomic data (energy levels and oscillator strengths) consistent with experimental data. We make use of the Flexible Atomic Code software package [4] that relies on a single mean potential computed for a single fractional fictitious configuration (FMC), allowing for great computational efficiency. Our method exploits a Sequential Model-Based Optimization (SMBO) procedure to find the best FMC that reproduces available experimental and/or ab-initio data. This allows us to improve the accuracy of final calculations while balancing efficiency and accuracy within our calculations.
In this talk, we will present results from large-scale calculations of data for relevant r-process elements computed using this optimization procedure, with great focus on lanthanide and actinides. Furthermore, we investigated how this optimization technique affects our calculations while comparing with results from other atomic structure codes in order to quantify the uncertainty in atomic data produced using different methodologies. Our goal is to provide a more reliable, while still complete set of atomic data for relevant lanthanides and actinides in the expanding ejecta.
References
[1] R. F. Silva, J. M. Sampaio, P. Amaro, A. Flörs, G. Martínez-Pinedo, and J. P. Marques, “Structure Calculations in Nd III and U III Relevant for Kilonovae Modelling,” Atoms, vol. 10, no. 1, p. 18, Mar. 2022, doi: 10.3390/atoms10010018.
[2] A. Flörs et al., Opacities of Singly and Doubly Ionised Neodymium and Uranium for Kilonova Emission Modeling. arXiv, 2023. doi: 10.48550/arXiv.2302.01780.
[3] N. Domoto, M. Tanaka, D. Kato, K. Kawaguchi, K. Hotokezaka, and S. Wanajo, “Lanthanide Features in Near-infrared Spectra of Kilonovae,” The Astrophysical Journal, vol. 939, no. 1, p. 8, Oct. 2022, doi: 10.3847/1538-4357/ac8c36.
[4] M. F. Gu, “The Flexible Atomic Code,” Canadian Journal of Physics, vol. 86, no. 5, pp. 675–689, May 2008, doi: 10.1139/p07-197.
