We critically examine recent claims of a high solar metallicity by von Steiger & Zurbuchen (2016, vSZ16) based onin situ measurements of the solar wind, rather than the standard spectroscopically inferred abundances (Asplund et al. 2009, hereafter AGSS09). We test the claim by Vagnozzi et al. (2016) that a composition based on the solar wind enables one to construct a standard solar model in agreement with helioseismological observations and thus solve the decades-old solar modelling problem. We show that, although some helioseismological observables are improved compared to models computed with spectroscopic abundances, most are in fact worse. The high abundance of refractory elements leads to an overproduction of neutrinos, with a predicted B-8 flux that is nearly twice its observed value, and Be-7 and CNO fluxes that are experimentally ruled out at high confidence. A combined likelihood analysis shows that models using the vSZ16 abundances are worse than AGSS09 despite a higher metallicity. We also present astrophysical and spectroscopic arguments showing the vSZ16 composition to be an implausible representation of the solar interior, identifying the first ionization potential effect in the outer solar atmosphere and wind as the likely culprit.

The chemical composition of the Sun is an essential piece of reference data for astronomy, cosmology, astroparticle, space and geophysics: elemental abundances of essentially all astronomical objects are referenced to the solar composition, and basically every process involving the Sun depends on its composition. This article, dealing with the intermediate-mass elements Na to Ca, is the first in a series describing the comprehensive re-determination of the solar composition. In this series we severely scrutinise all ingredients of the analysis across all elements, to obtain the most accurate, homogeneous and reliable results possible. We employ a highly realistic 3D hydrodynamic model of the solar photosphere, which has successfully passed an arsenal of observational diagnostics. For comparison, and to quantify remaining systematic errors, we repeat the analysis using three different 1D hydrostatic model atmospheres (marcs, miss and Holweger & Muller 1974, Sol. Phys., 39, 19) and a horizontally and temporally-averaged version of the 3D model (〈3D〉). We account for departures from local thermodynamic equilibrium (LTE) wherever possible. We have scoured the literature for the best possible input data, carefully assessing transition probabilities, hyperfine splitting, partition functions and other data for inclusion in the analysis. We have put the lines we use through a very stringent quality check in terms of their observed profiles and atomic data, and discarded all that we suspect to be blended. Our final recommended 3D+NLTE abundances are: log e = 6:21 ± 0:04, log e = 7:59 ± 0:04, log e = 6:43 ± 0:04, log e = 7:51 ± 0:03, log e = 5:41 ± 0:03, log e = 7:13 ± 0:03, log e = 5:04 ± 0:05 and log e = 6:32 ± 0:03. The uncertainties include both statistical and systematic errors. Our results are systematically smaller than most previous ones with the 1D semi-empirical Holweger & Muller model, whereas the 〈3D〉 model returns abundances very similar to the full 3D calculations. This analysis provides a complete description and a slight update of the results presented in Asplund et al. (2009, ARA&A, 47, 481) for Na to Ca, and includes full details of all lines and input data used.

The Sun, the closest and most well studied of stars, is generally used as a standard that other stars are compared to. Models of the Sun are constantly tested with helioseismic data. These data allow us to probe the internal structure and dynamics of the Sun. Among the main sources of the data is the SOHO spacecraft that has been continuously observing the Sun for more than a solar cycle. Current solar models, although good, do not include all the physical processes that are present in the Sun. In this chapter we focus on specific inputs to solar models and discuss generally neglected dynamical physical processes whose inclusion could result in models that are much better representatives of the Sun.

We redetermine the abundances of all iron group nuclei in the Sun, based on neutral and singly-ionised lines of Sc, Ti, V, Mn, Fe, Co and Ni in the solar spectrum. We employ a realistic 3D hydrodynamic model solar atmosphere, corrections for departures from local thermodynamic equilibrium (NLTE), stringent line selection procedures and high quality observational data. We have scoured the literature for the best quality oscillator strengths, hyperfine constants and isotopic separations available for our chosen lines. We find log epsilon(Sc) = 3.16 +/- 0.04, log epsilon(Ti) = 4.93 +/- 0.04, log epsilon(V) = 3.89 +/- 0.08, log epsilon(Cr) = 5.62 +/- 0.04, log epsilon(Mn) = 5.42 +/- 0.04, log epsilon(Fe) = 7.47 +/- 0.04, log epsilon(Co) = 4.93 +/- 0.05 and log epsilon(Ni) = 6.20 +/- 0.04. Our uncertainties factor in both statistical and systematic errors (the latter estimated for possible errors in the model atmospheres and NLTE line formation). The new abundances are generally in good agreement with the CI meteoritic abundances but with some notable exceptions. This analysis constitutes both a full exposition and a slight update of the preliminary results we presented in Asplund et al. (2009, ARA&A, 47, 481), including full line lists and details of all input data we employed.

We re-evaluate the abundances of the elements in the Sun from copper (Z = 29) to thorium (Z = 90). Our results are mostly based on neutral and singly-ionised lines in the solar spectrum. We use the latest 3D hydrodynamic solar model atmosphere, and in a few cases also correct for departures from local thermodynamic equilibrium (LTE) using non-LTE (NLTE) calculations performed in 1D. In order to minimise statistical and systematic uncertainties, we make stringent line selections, employ the highest-quality observational data and carefully assess oscillator strengths, hyperfine constants and isotopic separations available in the literature, for every line included in our analysis. Our results are typically in good agreement with the abundances in the most pristine meteorites, but there are some interesting exceptions. This analysis constitutes both a full exposition and a slight update of the relevant parts of the preliminary results we presented in Asplund et al. (2009, ARA&A, 47, 481), including full line lists and details of all input data that we have employed.

We summarize here the discussions around photospheric constraints, current uncertainties in models of stellar atmospheres, and reports on ongoing spectroscopic surveys. Rather than a panorama of the state of the art, we chose to present a list of open questions that should be investigated in order to improve future analyses.

We follow the evolution since 1989 of element abundance determinations in the solar photosphere. We describe how the largely used high metallicity mixtures (Z = 0.02 to 0.017) of Anders & Grevesse (1989), Grevesse & Noels (1993) and Grevesse & Sauval (1998) have been obtained and explain why these mixtures should not be used anymore. They are to be replaced by the more recent mixture of Asplund et al. (2009) which results from the first comprehensive and homogeneous analysis for many decades. We describe the main characteristics of this work and discuss some impacts of this low Z (Z = 0.0134) mixture. We also comment on another recent analysis by Caffau et al. (2011) that leads to somewhat larger metal abundances.

We show why the solar chemical composition of [1] (GN93) and the similar values of [2] (AG89) and [3] (GS98), characterized by values of the metallicity of the order of 0.017 to 0.020, largely used in solar and stellar modeling, are now obsolete. They should be replaced by the new and more precise results of [4] (AGSS09), with a much lower metallicity of 0.0134.

We review the current status of our knowledge of the chemical composition of the sun and present a redetermination of the solar abundances of all available elements. These new results have recently been published by Asplund et al. (2009). The basic ingredients of this work, the main results and their implications are discussed. We show why the abundances of the main contributors to the metallicity have decreased and why the old high solar metallicity, Z similar to 0.02, is definitely obsolete and should not he used anymore. We also show why other recent analyzes of the solar composition report solar metallicities somewhat larger than the one we recommend.

We review the current status of our knowledge of the chemical composition of the sun and present a redetermination of the solar abundances of all available elements. These new results have very recently been published by Asplund et al. (2009). The basic ingredients of this work, the main results and their implications are discussed.

We have very recently re-determined the abundances of nearly all the available chemical elements in the solar photosphere, from lithium to thorium (Asplund et al. Annu. Rev. Astron. Astrophys. 47, 481 (2009)). This new complete and homogeneous analysis results from a very careful selection of spectral lines of all the indicators of the abundances present in the solar photospheric spectrum, from a discussion of the atomic and molecular data, and from an analysis of these lines based on a new 3D model of the solar outer layers, taking non-LTE effects into account when possible. We present these new results, compare them with other recent solar data as well as with recent results for the solar neighborhood, and discuss some of their most important implications as well as some of the atomic data we still urgently need.

We present a redetermination of the solar abundances of all available elements. The new results have very recently been published by Asplund et al. (Annu. Rev. Astron. Astrophys. 47:481,2009). The basic ingredients of this work, the main results and some of their implications are summarized hereafter.

The solar photospheric abundance of ruthenium is revised on the basis of a new set of oscillator strengths derived for Ru I transitions with wavelengths in the spectral range 2250–4710 A. The new abundance value (in the usual logarithmic scale where the solar hydrogen abundance is equal to 12.00), ARu = 1.72 ± 0.10, is in agreement with the most recent meteoritic result, ARu = 1.76 ± 0.03. The accuracy of the transition probabilities, obtained using a relativistic Hartree–Fock model including core-polarization effects, has been assessed by comparing the theoretical lifetimes with previous experimental results. A comparison is also made with new measurements performed in this work by the time-resolved laser-induced fluorescence spectroscopy for 10 highly excited odd-parity levels of Ru I.

Determinations of the solar oxygen content relying on the neutral forbidden transition at 630 nm depend upon the nickel abundance, due to a Ni I blend. Here, we rederive the solar nickel abundance, using the same ab initio three-dimensional hydrodynamic model of the solar photosphere employed in the recent revision of the abundances of C, N, O, and other elements. Using 17 weak, unblended lines of Ni I together with the most accurate atomic and observational data available, we find log is an element of(Ni) = 6.17 +/- 0.02 ( statistical) +/- 0.05 ( systematic), a downward shift of 0.06-0.08 dex relative to previous abundances based on one-dimensional model atmospheres. We investigate the implications of the new nickel abundance for studies of the solar oxygen abundance based on the [O I] 630 nm line in the quiet Sun. Furthermore, we demonstrate that the oxygen abundance implied by the recent sunspot spectropolarimetric study of Centeno & Socas-Navarro needs to be revised downward from log is an element of(O) = 8.86 +/- 0.07 to 8.71 +/- 0.10. This revision is based on the new nickel abundance, the application of the best available gf value for the 630 nm forbidden oxygen line, and a more transparent treatment of CO formation. Determinations of the solar oxygen content relying on forbidden lines now appear to converge around log is an element of(O) = 8.7.

We present our current knowledge of the solar chemical composition based on the recent significant downward revision of the solar photospheric abundances of the most abundant metals. These new solar abundances result from the use of a 3D hydrodynamic model of the solar atmosphere instead of the classical 1D hydrostatic models, accounting for departures from LTE, and improved atomic and molecular data. With these abundances, the new solar metallicity, Z, decreases to Z=0.012, almost a factor of two lower than earlier widely used values. We compare our values with data from other sources and analyse a number of impacts of these new photospheric abundances. While resolving a number of longstanding problems, the new 3D-based solar photospheric composition also poses serious challenges for the standard solar model as judged by helioseismology.

CO spectral line formation in the Sun has long been a source of consternation for solar physicists, as have the elemental abundances it seems to imply. We modelled solar CO line formation using a realistic, ab initio, time-dependent 3D radiative-hydrodynamic model atmosphere. Results were compared with observations from the space-based ATMOS experiment. We employed weak 12C16O, 13C16O and 12C18O lines from the fundamental and first overtone bands to determine the solar carbon abundance, as well as the 12C/13C and 16O/18O isotopic ratios. A weighted carbon abundance of log epsilonC = 8.39 +-0.05 was found. We note with satisfaction that the derived abundance is identical to our recent 3D determination based on CI, [C I], C2 and CH lines. Identical calculations were carried out using 1D models, but only the 3D model was able to produce abundance agreement between different CO lines and the other atomic and molecular diagnostics. Solar 12C/13C and 16O/18O ratios were measured as 86.8+3.9-3.7 (delta13C = 30+46-44) and 479+29-28 (delta18O = 41+67-59), respectively. These values may require current theories of solar system formation to be revised. Excellent agreement was seen between observed and predicted weak CO line shapes, without invoking micro- or macroturbulence. Agreement breaks down for the strongest CO lines however, which are formed in very high atmospheric layers. The simplest explanation is that temperatures are overestimated in the highest layers of the 3D simulation. Thus, our analysis supports the presence of a COmosphere above the traditional photospheric temperature minimum, with an average temperature of less than 4000K. The shortcoming of the model atmosphere is not surprising, given that it was never intended to properly describe such high layers.

Recent 3D, NLTE analysis of the solar spectrum (Asplund et al.2005b, Part I; Asplund et al. 2005a) have led to a signican t reduction of the CNO and Ne abundances leading to a (Z=X)s 30% smaller than previously recommended value. The corresponding decrease in opacity increases dramatically the discrepancies between the sound-speed derived from helioseismology and our new standard solar models (SSM). We present in this paper some numerical experiments trying to reduce this discrepancy.