Speaker
Description
We will review atomic processes relevant to kilonovae and the current
state-of-play in servicing the needs of modellers.
The atomic processes relevant to kilonovae separate into their two plasma phases: the first few days, where LTE holds, and the subsequent non-LTE phase. In LTE, where fractional ionic abundances and level populations are given by the Saha--Boltzmann equations, the main focus is on generating opacities for the first few ionization stages of the lanthanides and actinides. Non-LTE is more problematic: the ionization balance now requires calculation of specific ionization and recombination rate coefficients while electron-impact excitation (EIE) rate coefficients and associated radiative rates are the minimum requirement for level population determination. Again for similar heavy ions as LTE.
LTE. Over the past decade or so a number of groups have calculated lanthanide (more so) and actinide (less so) opacities [1,2,3,4,5,6]. We will review this work and comment on issues that have been raised recently such as the utility of expansion vs line-binned opacities [2,7] and partition functions [8]. And also, what remains to be done, particularly with respect to cross comparison and validation of such data calculated using various atomic codes (Autostructure, Cowan, FAC, GRASP, HULLAC, RATS \& CATS ...). The state of-play here is much less mature than for the solar case [9].
NLTE. It can be argued that the main uncertainty in the ionization balance here is due to the sparsity of dielectronic recombination (DR) rate coefficients for low-charge lanthanide and actinides. Radiative recombination (RR) and ionization are more amenable to being described by simple semi-empirical formula, benchmarked by a few detailed calculations. In contrast, while there is the Burgess General Formula for DR, it does not model more complex systems well and it fails completely at low-to-moderate temperatures. Heavy element DR (W for magnetic fusion and Sn for nanolithography) has stimulated the development of the Autostructure code [10,11] to describe these complex systems. Here, we will present some preliminary results for the DR of Te$^{2+}$, which are to be compared with those from HULLAC (Banerjee, Private Communication, 2023) and contrasted with those for RR. Regarding EIE, we note that Dirac R-matrix calculations for key kilonovae species are underway (Ballance, Private Communication, 2023).
[1] D. Kasen \etal, ApJ 774, 25 (2013)
[2] C. J. Fontes \etal, MNRAS 493, 4143 (2020)
[3] C. J. Fontes \etal, MNRAS 519, 2862 (2023)
[4] M. Tanaka \etal, MNRAS 496, 1369 (2020)
[5] S. Banerjee \etal, ApJ 934, 117 (2022)
[6] H Carvajal Gallego \etal, MNRAS 518, 332 (2023)
[7] H Carvajal Gallego \etal, MNRAS 522, 312 (2023)
[8] H Carvajal Gallego \etal, EPJD 77, 72 (2023)
[9] F. Delahaye \etal, MNRAS 508, 421 (2021)
[10] http://amdpp.phys.strath.ac.uk/autos/
[11] N. R. Badnell, Comp. Phys. Commun. 182, 1528 (2011).
