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

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.