Electron-impact excitation of zirconium <scp>i</scp>–<scp>iii</scp> in support of neutron star merger diagnostics

ABSTRACT Recent observations and analyses of kilonova spectra as a result of neutron star mergers require accurate and complete atomic structure and collisional data for interpretation. Ideally, the atomic data sets for elements predicted to be abundant in the ejecta should be experimentally calibrated. For near-neutral ion stages of zirconium in particular, the A-values and the associated excitation/de-excitation rates are required from collision calculations built upon accurate structure models. The atomic orbitals required to perform the structure calculations may be calculated using a Multi-Configuration-Dirac-Fock (MCDF) approximation implemented within the General Relativistic Atomic Structure Package (grasp0). Optimized sets of relativistic atomic orbitals are then imported into electron-impact excitation collision calculations. A relativistic R-matrix formulation within the Dirac Atomic R-matrix Code (darc) is employed to compute collision strengths, which are subsequently Maxwellian convolved to produce excitation/de-excitation rates for a wide range of electron temperatures. These atomic data sets subsequently provide the foundations for non-local thermodynamic equilibrium collisional-radiative models. In this work, all these computations have been carried out for the first three ion stages of zirconium (Zr i–iii) with the data further interfaced with collisional-radiative and radiative transfer codes to produce synthetic spectra that can be compared with observation.