On the importance of using realistic partition functions in kilonova opacity calculations

In the present work, we report an investigation on the importance of using realistic partition functions in the opacity calculations of lanthanide ions whether they are moderately or lowly ionized. In order to do this, atomic data for various moderately charged samarium (Sm V–XI) and lowly charged neodymium (Nd II–IV) ions were calculated by the pseudo-relativistic Hartree–Fock method (HFR) and then, used to compute the expansion opacities for conditions characterizing the ejecta of kilonovae observed as a result of neutron star mergers, with a particular attention given to the partition function computations. Graphical abstract