  Binary neutron star mergers are thought to be one of the dominant sites of
production for rapid neutron capture elements, and the source of platinum and
gold in the Universe. Since the discovery of the binary neutron star merger
GW170817, and its associated kilonova AT2017gfo, numerous works have attempted
to determine the composition of its outflowing material, but they have been
hampered by the lack of complete atomic data. Here we demonstrate how inclusion
of new atomic data in synthetic spectra calculations can provide insights and
constraints on the production of the heaviest elements. We employ theoretical
atomic data for neutral, singly- and doubly-ionised platinum and gold, to
generate photospheric and simple nebular-phase model spectra for kilonova-like
ejecta properties. We make predictions for the locations of strong transitions,
which could feasibly appear in the spectra of kilonovae that are rich in these
species. We use GRASP0 to generate the underlying atomic structure and TARDIS
to model the diffusion phase showing that the strongest features lie in the
ultra-violet region. We identify low-lying electric quadrupole and magnetic
dipole transitions that may give rise to forbidden lines when the ejecta
becomes optically thin. The strongest lines lie beyond 8000 Angstroms,
motivating high quality near-infrared spectroscopic follow-up of kilonova
candidates. We compare our model spectra to the observed spectra of AT2017gfo,
and conclude that no platinum or gold signatures are prominent in the ejecta.
This work demonstrates how new atomic data of heavy elements can be included in
radiative transfer calculations, and motivates future searches for elemental
signatures.
