The solar sulphur abundance in view of large-scale atomic structure calculations and 3D non-LTE models

¹ Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Box 516 SE-751 20 Uppsala, Sweden
² National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China
³ Centre Spatial de Liège, Université de Liège, avenue Pré Aily, B-4031 Angleur-Liège, Belgium
⁴ Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 août, 17, B5C, B-4000 Liège, Belgium
⁵ Busek Center for Meteorite Studies, Arizona State University, Tempe, Arizona 85287-6004, USA
⁶ Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA

^⋆ Corresponding author: anish.amarsi@physics.uu.se

Received: 3 August 2025
Accepted: 5 September 2025

Abstract

The solar chemical composition is a fundamental yardstick in astrophysics and the topic of heated debate in recent literature. We re-evaluated the abundance of sulphur in the photosphere by studying seven S I lines in the solar disc-centre intensity spectrum. Our analysis considers independent sets of experimental and theoretical oscillator strengths together with, for the first time, three-dimensional non-local thermodynamic equilibrium (3D non-LTE) S I spectrum synthesis. Our best estimate is A(S) = 7.06 ± 0.04, which is 0.06 − 0.10 dex lower than that in commonly used compilations of the solar chemical composition. Our lower solar sulphur abundance deviates from that in CI chondrites and thereby supports the case for a systematic difference between the composition of the solar photosphere and of CI chondrites that is correlated with 50% condensation temperature. We suggest that precise laboratory measurements of S I oscillator strengths and abundance analyses using 3D magnetohydrodynamic models of the solar photosphere be conducted to further substantiate our conclusions.