Kilonova ejecta opacity inferred from new large-scale HFR atomic calculations in all elements between Ca (Z = 20) and Lr (Z = 103)

TL;DR

This paper provides comprehensive atomic data and opacity calculations for elements Z=20 to Z=103 relevant to kilonova modeling, revealing that lanthanides are not the dominant opacity sources and emphasizing the importance of detailed composition in opacity estimates.

Contribution

It introduces new large-scale HFR atomic data and opacity calculations for all elements from Ca to Lr, improving kilonova models by accounting for detailed elemental contributions.

Findings

Lanthanides are not the dominant opacity sources on average.

Atomic data and opacity tables for all relevant elements are publicly available.

Considering detailed composition affects kilonova light curve modeling.

Abstract

In the context of kilonova (KN) modeling, the present work focusses on large-scale atomic data and opacity computations for all heavy elements from Ca to Lr, with a special effort on lanthanides and actinides, for a grid of typical KN ejecta conditions between one day and one week after the merger (corresponding to the LTE photosphere phase of the KN ejecta). In order to do so, we used the pseudo-relativistic Hartree-Fock (HFR) method, in which the choice of the interaction configuration model is of crucial importance. In this paper, HFR atomic data and opacities for all elements between Ca (Z = 20) and Lr (Z = 103) are presented, with a special focus on lanthanides and actinides. Besides, we also discuss the contribution of every single element to the total KN ejecta opacity for a given neutron star merger model, depending on their Planck mean opacities and elemental abundances. An important result is that lanthanides are found to not be the dominant sources of opacity, at least on average. The impact on KN light curves of considering such atomic-physics based opacity data instead of typical crude approximation formulae is also evaluated. In addition, the importance of taking the ejecta composition into account directly in the expansion opacity determination (instead of estimating single-element opacities) is highlighted. A database containing all the relevant atomic data and opacity tables has also been created and published online along with this work.