Benchmarking computationally-effcient approximations for collisional and radiative data in weakly-charged Sr and Te ions for large-scale production of atomic data relevant to NLTE kilonova modeling
POSTER
Abstract
Gravitational waves emitted following a neutron star merger (NSM) were observed for the first time in 2017 (GW170817). Its electromagnetic counterpart, known as a kilonova (KN), whose emission is powered by the newly synthesized r-process elements, was also detected (AT2017gfo). More recently, late-time spectra of a new KN were observed by the JWST (AT2023vfi).
NSMs are now recognized as prime sites of heavy element production through r-process nucleosynthesis, while the production of those heavy elements remains incompletely understood so far. KN modeling has thus become a topic of significant scientific interest. During the first few days after the merger, the KN ejecta is in a photospheric phase, where the LTE assumption is valid, simplifying the calculation of atomic energy level populations through Boltzmann and Saha equations in order to determine the ejecta opacity. About a week post-merger, the KN ejecta enters its nebular phase, where NLTE effects become important, making the determination of energy level populations extremely complex.
To model nebular-phase KN spectra, it is thus necessary to account for all radiative and collisional processes that can (de)populate the various energy levels of the ejecta ions, such as radiative transitions, electron-impact collisions, photoionization, as well as radiative and dielectronic recombinations. In this work, we model several radiative and collisional processes in heavy ions (potentially) observed in KN spectra, such as Sr II and Te III, by means of two different approaches: the Plane-Wave Born approximation as implemented in the pseudo-relativistic Hartree-Fock (HFR) method and a Distorted-Wave approach. The resulting atomic data are compared with values available in the literature obtained using the more complex R-matrix method to assess the validity of our approximations for the purpose of large-scale atomic data production for all heavy elements (in particular, lanthanides and actinides) suspected to be present in the KN ejecta.
NSMs are now recognized as prime sites of heavy element production through r-process nucleosynthesis, while the production of those heavy elements remains incompletely understood so far. KN modeling has thus become a topic of significant scientific interest. During the first few days after the merger, the KN ejecta is in a photospheric phase, where the LTE assumption is valid, simplifying the calculation of atomic energy level populations through Boltzmann and Saha equations in order to determine the ejecta opacity. About a week post-merger, the KN ejecta enters its nebular phase, where NLTE effects become important, making the determination of energy level populations extremely complex.
To model nebular-phase KN spectra, it is thus necessary to account for all radiative and collisional processes that can (de)populate the various energy levels of the ejecta ions, such as radiative transitions, electron-impact collisions, photoionization, as well as radiative and dielectronic recombinations. In this work, we model several radiative and collisional processes in heavy ions (potentially) observed in KN spectra, such as Sr II and Te III, by means of two different approaches: the Plane-Wave Born approximation as implemented in the pseudo-relativistic Hartree-Fock (HFR) method and a Distorted-Wave approach. The resulting atomic data are compared with values available in the literature obtained using the more complex R-matrix method to assess the validity of our approximations for the purpose of large-scale atomic data production for all heavy elements (in particular, lanthanides and actinides) suspected to be present in the KN ejecta.
Publication: Deprince, J., & Maison, L. (2026). Benchmarking the Plane-Wave Born and Distorted Waves approximations for electron-impact collision strength computations: the sample case of Sr II. Plasma and Fusion Research, in press. arXiv:2509.07684 [physics.atom-ph].
Presenters
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Jerome Deprince
- University of Mons