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

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.