Abstract
Context.The chemical composition of the Sun is a fundamental yardstick in astronomy, relative to which essentially all cosmic objects are referenced. As such, having accurate knowledge of the solar elemental abundances is crucial for an extremely broad range of topics.Aims.We reassess the solar abundances of all 83 long-lived elements, using highly realistic solar modelling and state-of-the-art spectroscopic analysis techniques coupled with the best available atomic data and observations.Methods.The basis for our solar spectroscopic analysis is a three-dimensional (3D) radiative-hydrodynamical model of the solar surface convection and atmosphere, which reproduces the full arsenal of key observational diagnostics. New complete and comprehensive 3D spectral line formation calculations taking into account of departures from local thermodynamic equilibrium (non-LTE) are presented for Na, Mg, K, Ca, and Fe using comprehensive model atoms with reliable radiative and collisional data. Our newly derived abundances for C, N, and O are based on a 3D non-LTE analysis of permitted and forbidden atomic lines as well as 3D LTE calculations for a total of 879 molecular transitions of CH, C2, CO, NH, CN, and OH. Previous 3D-based calculations for another 50 elements are re-evaluated based on updated atomic data, a stringent selection of lines, improved consideration of blends, and new non-LTE calculations available in the literature. For elements where spectroscopic determinations of the quiet Sun are not possible, the recommended solar abundances are revisited based on complementary methods, including helioseismology (He), solar wind data from the Genesis sample return mission (noble gases), sunspot observations (four elements), and measurements of the most primitive meteorites (15 elements).Results.Our new improved analysis confirms the relatively low solar abundances of C, N, and O obtained in our previous 3D-based studies: logϵC = 8.46 ± 0.04, logϵN = 7.83 ± 0.07, and logϵO = 8.69 ± 0.04. Excellent agreement between all available atomic and molecular indicators is achieved for C and O, but for N the atomic lines imply a lower abundance than for the molecular transitions for unknown reasons. The revised solar abundances for the other elements also typically agree well with our previously recommended values, with only Li, F, Ne, Mg, Cl, Kr, Rb, Rh, Ba, W, Ir, and Pb differing by more than 0.05 dex. The here-advocated present-day photospheric metal mass fraction is only slightly higher than our previous value, mainly due to the revised Ne abundance from Genesis solar wind measurements:Xsurface = 0.7438 ± 0.0054,Ysurface = 0.2423 ± 0.0054,Zsurface = 0.0139 ± 0.0006, andZsurface/Xsurface = 0.0187 ± 0.0009. Overall, the solar abundances agree well with those of CI chondritic meteorites, but we identify a correlation with condensation temperature such that moderately volatile elements are enhanced by ≈0.04 dex in the CI chondrites and refractory elements possibly depleted by ≈0.02 dex, conflicting with conventional wisdom of the past half-century. Instead, the solar chemical composition more closely resembles that of the fine-grained matrix of CM chondrites with the expected exception of the highly volatile elements.Conclusions.Updated present-day solar photospheric and proto-solar abundances are presented for 83 elements, including for all long-lived isotopes. The so-called solar modelling problem – a persistent discrepancy between helioseismology and solar interior models constructed with a low solar metallicity similar to that advocated here – remains intact with our revised solar abundances, suggesting shortcomings with the computed opacities and/or treatment of mixing below the convection zone in existing standard solar models. The uncovered trend between the solar and CI chondritic abundances with condensation temperature is not yet understood but is likely imprinted by planet formation, especially since a similar trend of opposite sign is observed between the Sun and solar twins.
Highlights
The pursuit of detailed knowledge of the elemental abundances in the Solar System has played a critical role in the development of modern astronomy
At least for atomic and ionic species in the disc-centre intensity spectrum of the Sun, the full 3D non-local thermodynamic equilibrium (LTE) result for Mn should be similar to the 3D non-LTE abundance, as we have found in our investigations of Li, C, N, O, Na, Mg, Al, Si, K, Ca, and Fe
The elemental abundances derived and presented here are a further stepping stone towards the advancement of our understanding of the solar chemical composition, which is of such crucial importance for astronomy as a whole
Summary
The pursuit of detailed knowledge of the elemental abundances in the Solar System has played a critical role in the development of modern astronomy. A huge body of influential and careful work on determining the solar chemical composition has been carried out over several decades using such 1D solar atmosphere models (e.g., Goldberg et al 1960; Lambert 1968, 1978; Grevesse & Sauval 1973, 1999; Ross & Aller 1976; Holweger et al 1991; Blackwell et al 1995) This has often been done in close collaboration with atomic physicists measuring or computing transition probabilities and other necessary input data, which is a highly successful synergy (e.g., Garz et al 1969; Andersen et al 1975; Biemont et al 1981, 1991; Hannaford et al 1992; Barklem et al 2000; Lawler et al 2001, 2013; Johansson et al 2003; Ljung et al 2006; Blackwell-Whitehead & Bergemann 2007; Den Hartog et al 2019). We provide estimates for the proto-solar (isotopic) abundances where the effects of atomic diffusion, nuclear burning, and radioactive decay have been taken into account, as well as the present-day and protosolar mass fractions of H, He, and heavy elements
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