Characterisation of a high-resolution spectroscopic setup for experimental determination of transition probabilities of neodymium

Abstract

Accurate atomic data for lanthanides, particularly neodymium (Nd), are essential for astrophysical applications, including modelling kilonova opacity and determining stellar abundances. However, reliable experimental data for these ions remain scarce due to the spectral complexity of the lanthanides. In this study, we present a comprehensive characterisation of a high-resolution spectroscopic setup optimised for measuring transition probabilities of Nd lines. The system consists of a 1.5 m Czerny-Turner spectrometer coupled to a high-sensitivity CMOS detector, achieving a resolving power of up to 150,000. A modified hollow cathode lamp, originally developed at Imperial College London, was used to generate a stable neodymium plasma using argon as a carrier gas. We include an in-depth characterisation of our high-resolution setup, including spectral calibration, resolution assessment, instrument response function, and CMOS noise analysis. The validity of the partial local thermodynamic equilibrium (pLTE) assumption in the hollow cathode lamp was tested by measuring transition probabilities for 15 Nd II lines in the spectral range 378–521 nm. The derived transition probabilities show agreement within 30% of the reference values. This validation paves the way for accurate measurements of currently unreported Nd III transition probabilities, providing critical data for future astrophysical modelling efforts.