Collisional and Radiative Data for Tellurium ions in Kilonovae modelling and Laboratory Benchmarks

TL;DR

This paper provides new atomic data for tellurium ions relevant to kilonovae spectra modeling, including energy levels, transition probabilities, and collision strengths, aiding in more accurate spectral simulations and laboratory benchmarks.

Contribution

It introduces comprehensive atomic structure and collision data for Te I-III, enabling improved NLTE modeling of kilonovae spectra and laboratory benchmarks.

Findings

NLTE simulations show Te III 2.1 μm line prominence increases as ejecta cools.

New atomic data results in negligible spectral changes at early epochs.

Proposed line ratios facilitate observational and laboratory validation of atomic data.

Abstract

Tellurium is a primary candidate for the identification of the 2.1 $\mu$m emission line in kilonovae (KNe) spectra AT2017gfo and GRB230307A. Despite this, there is currently an insufficient amount of atomic data available for this species. We calculate the required atomic structure and collisional data, particularly the data required for accurate Non-Local-Thermodynamic-Equilibrium (NLTE) modelling of the low temperatures and densities in KNe. We use a Multi-Configurational-Dirac-Hartree-Fock method to produce optimised one-electron orbitals for Te {\sc i}-{\sc iii}. As a result energy levels and Einstein A-coefficients for Te {\sc i}-{\sc iii} have been calculated. These orbitals are then employed within Dirac $R$-matrix collision calculations to provide electron-impact-excitation collision strengths that were subsequently averaged according to a thermal Maxwellian distribution. Subsequent \textsc{tardis} simulations using this new atomic data reveal no significant changes to the synthetic spectra due to the very minor contribution of Te at early epochs. NLTE simulations with the ColRadPy package reveal optically thin spectra consistent with the increasing prominence of the Te {\sc iii} 2.1 $\mu$m line as the KNe ejecta cools. This is reinforced by the estimation of luminosities at nebular KNe conditions. New line ratios for both observation and laboratory benchmarks of the atomic data are proposed.