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Fundamental Atomic Data for Platinum Group Elements in Neutron Star Merger Plasmas

Presentation #117.01 in the session Laboratory Astrophysics (LAD) Division Meeting: The Salty Solar System I.

Published onJun 29, 2022
Fundamental Atomic Data for Platinum Group Elements in Neutron Star Merger Plasmas

Most elements heavier than ruthenium (Ru, Z = 44) are thought to be formed to some extent in neutron star mergers. The detection of gravitational waves from a neutron star merger in 2017 (see e.g. [1,2,3]) has generated increased interest and scrutiny of fundamental atomic data for opacity calculations of heavy elements formed through the rapid neutron capture process (r-process). For the third r-process peak — the platinum group — we have undertaken efforts to expand and benchmark the necessary atomic data through combined experimental and theoretical efforts. I will discuss portions of my dissertation, Atomic Data Needs in Laboratory Astrophysics: Experimental Methods for Spectroscopy and Charge Exchange with Ions, which included spectroscopic studies of neutral and ionized gold (Au I and Au II) in a high-temperature laboratory plasma. Using the Compact Toroidal Hybrid (CTH) stellarator/tokamak at Auburn University, we successfully identified over 150 dipole-allowed transitions of both Au I and Au II at near-ultraviolet and optical wavelengths [4]. Following this work, we have expanded our efforts to other elements (Pt, Ir), and extended our efforts to electron impact processes.

I will discuss the CTH experiments and their role in benchmarking fundamental atomic data for heavy elements, including energy levels, transition rates, and collision data. Specifically, we address the need for electron impact excitation rates and an understanding of the effects of metastable levels on collision dynamics in both low- and high-temperature environments. Using the open source collisional-radiative solver ColRadPy [5] and electron impact excitation data produced by R-matrix calculations, we explored the excitation dynamics of these heavy systems under Neutron Star Merger-like plasma conditions [6]. I will discuss the effects of metastable levels and their contributions to emission lines, and more importantly the deviations from Local Thermodynamic Equilibrium (LTE) for these and other heavy elements.

[1] Abbott et al. 2017a, Phys. Rev. Lett. 119, 161101.

[2] Abbott et al. 2017b, Astrophys. J. 848, L13.

[3] Abbott et al. 2017c, Astrophys. J. 848, L12.

[4] Bromley et al. 2021, The Astrophysical Journal Supplement Series 250, 19.

[5] Johnson, Loch, and Ennis 2019, Nuclear Materials and Energy 20, 100579.

[6] McCann et al. 2021, Monthly Notices of the Royal Astronomical Society 509, 4723-4735.

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