Electron impact excitation of Te <scp>iv</scp> and <scp>v</scp> and level resolved R-matrix photoionization of Te  <scp>i–iv</scp> with application to modelling of AT2017gfo

ABSTRACT Spectral modelling of kilonovae (KNe) requires large amounts of collisional excitation and photoionization atomic data for lowly ionized (neutral, singly, and doubly ionized) species of heavy elements. Much of the data currently used is calculated using approximate hydrogenic results or adopts semi-empirical formulae. We present atomic data for ions of tellurium (Te) computed using the well-known R-matrix method. Results will also be presented for radiative and thermal collisions of Te iv and v, for which the required atomic data are also typically limited in the literature. The Multi-Configuration-Dirac–Hartree–Fock method is used to produce model atomic structures and radiative rates. These model structures are then used to calculate electron-impact-excitation and photoionization cross-sections. The resulting excitation and radiative rates are further used in a collisional radiative model to produce synthetic spectra, which are compared with observations. We also investigate the possibility of Te iv contributing to the 1.08 $\mu$m emission feature in the mid-epochs of AT2017gfo alongside the established P-Cygni feature of Sr ii.