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, C
2
, 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: log
ϵ
C
= 8.46 ± 0.04, log
ϵ
N
= 7.83 ± 0.07, and log
ϵ
O
= 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:
X
surface
= 0.7438 ± 0.0054,
Y
surface
= 0.2423 ± 0.0054,
Z
surface
= 0.0139 ± 0.0006, and
Z
surface
/
X
surface
= 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.
Carbon, nitrogen, and oxygen are the fourth, sixth, and third most abundant elements in the Sun. Their abundances remain hotly debated due to the so-called solar modelling problem that has persisted ...for almost 20 years. We revisit this issue by presenting a homogeneous analysis of 408 molecular lines across 12 diagnostic groups, observed in the solar intensity spectrum. Using a realistic 3D radiative-hydrodynamic model solar photosphere and local thermodynamic equilibrium (LTE) line formation, we find log
ϵ
C
= 8.47 ± 0.02, log
ϵ
N
= 7.89 ± 0.04, and log
ϵ
O
= 8.70 ± 0.04. The stipulated uncertainties mainly reflect the sensitivity of the results to the model atmosphere; this sensitivity is correlated between the different diagnostic groups, which all agree with the mean result to within 0.03 dex. For carbon and oxygen, the molecular results are in excellent agreement with our 3D non-LTE analyses of atomic lines. For nitrogen, however, the molecular indicators give a 0.12 dex larger abundance than the atomic indicators, and our best estimate of the solar nitrogen abundance is given by the mean: 7.83 dex. The solar oxygen abundance advocated here is close to our earlier determination of 8.69 dex, and so the present results do not significantly alleviate the solar modelling problem.
The solar chemical composition GREVESSE, N; ASPLUND, M; SAUVAL, A. J
Space science reviews,
06/2007, Volume:
130, Issue:
1-4
Conference Proceeding, Journal Article
Peer reviewed
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 a3D 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 afactor of two lower than earlier widely used values. We compare our values with data from other sources and analyse anumber of impacts of these new photospheric abundances. While resolving anumber of longstanding problems, the new 3D-based solar photospheric composition also poses serious challenges for the standard solar model as judged by helioseismology.
The chemical composition of the Sun Grevesse, N.; Asplund, M.; Sauval, A. J. ...
Astrophysics and space science,
07/2010, Volume:
328, Issue:
1-2
Journal Article
Peer reviewed
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.
Nitrogen is an important element in various fields of stellar and Galactic astronomy, and the solar nitrogen abundance is crucial as a yardstick for comparing different objects in the cosmos. In ...order to obtain a precise and accurate value for this abundance, we carried out N
I
line formation calculations in a 3D radiative-hydrodynamic
STAGGER
model solar atmosphere in full 3D non-local thermodynamic equilibrium (non-LTE). We used a model atom that includes physically motivated descriptions for the inelastic collisions of N
I
with free electrons and with neutral hydrogen. We selected five N
I
lines of high excitation energy to study in detail, based on their strengths and on their being relatively free of blends. We found that these lines are slightly strengthened from non-LTE photon losses and from 3D granulation effects, resulting in negative abundance corrections of around − 0.01 dex and − 0.04 dex, respectively. Our advocated solar nitrogen abundance is log
ɛ
N
= 7.77, with the systematic 1
σ
uncertainty estimated to be 0.05 dex. This result is consistent with earlier studies after correcting for differences in line selections and equivalent widths.
As a result of the high-quality constraints available for the Sun, we are able to carry out detailed combined analyses using neutrino, spectroscopic, and helioseismic observations. These studies lay ...the ground for future improvements of the key physical components of solar and stellar models because ingredients such as the equation of state, the radiative opacities, or the prescriptions for macroscopic transport processes of chemicals are then used to study other stars in the Universe. We study the existing degeneracies in solar models using the recent high-metallicity spectroscopic abundances by comparing them to helioseismic and neutrino data and discuss the effect on their properties of changes in the micro and macro physical ingredients. We carried out a detailed study of solar models computed with a high-metallicity composition from the literature based on averaged 3D models that were claimed to resolve the solar modelling problem. We compared these models to helioseismic and neutrino constraints. The properties of the solar models are significantly affected by the use of the recent OPLIB opacity tables and the inclusion of macroscopic transport. The properties of the standard solar models computed using the OPAL opacities are similar to those for which the OP opacities were used. We show that a modification of the temperature gradient just below the base of the convective zone is required to remove the discrepancies in solar models, particularly in the presence of macroscopic mixing. This can be simulated by a localised increase in the opacity of a few percent. We conclude that the existing degeneracies and issues in solar modelling are not removed by using an increase in the solar metallicity in contradiction to what has been suggested in the recent literature . Therefore, standard solar models cannot be used as an argument for a high-metallicity composition. While further work is required to improve solar models, we note that direct helioseismic inversions indicate a low metallicity in the convective envelope, in agreement with spectroscopic analyses based on full 3D models.
The solar photospheric oxygen abundance has been determined from O I, O I, OH vibration-rotation and OH pure rotation lines by means of a realistic time-dependent, 3D, hydrodynamical model of the ...solar atmosphere. In the case of the O I lines, 3D non-LTE calculations have been performed, revealing significant departures from LTE as a result of photon losses in the lines. We derive a solar oxygen abundance of log epsilon sub(O) = 8.66 plus or minus 0.05. All oxygen diagnostics yield highly consistent abundances, in sharp contrast with the results of classical 1D model atmospheres. This low value is in good agreement with measurements of the local interstellar medium and nearby B stars. This low abundance is also supported by the excellent correspondence between lines of very different line formation sensitivities, and between the observed and predicted line shapes and center-to-limb variations. Together with the corresponding down-ward revisions of the solar carbon, nitrogen and neon abundances, the resulting significant decrease in solar metal mass fraction to Z = 0.0126 can, however, potentially spoil the impressive agreement between predicted and observed sound speed in the solar interior determined from helioseismology.
Standard Solar Composition Grevesse, N; Sauval, A J
Space science reviews,
01/1998, Volume:
85, Issue:
1-2
Journal Article
Peer reviewed
We review the current status of our knowledge of the chemical composition of the Sun, essentially derived from the analysis of the solar photospheric spectrum. The comparison of solar and meteoritic ...abundances confirms that there is a very good agreement between the two sets of abundances. They are used to construct a Standard Abundance Distribution.
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 space-based observations from the ATMOS space shuttle experiment. We employed weak super(12) C super(16) O, super(13) C super(16) O and super(12) C super(18) O lines from the fundamental ( Delta v = 1) and first overtone ( Delta v = 2) bands to determine the solar carbon abundance, as well as the super(12) C/ super(13) C and super(16) O/ super(18) O isotopic ratios. A weighted solar carbon abundance of log\epsilon_{\rm C}=8.39 pm 0.05 was found. We note with satisfaction that the derived abundance is identical to our recent 3D determination based on C I, C I, C sub(2) and CH lines, increasing our confidence in the accuracy of both results. 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 super(12) C/ super(13) C and super(16) O/ super(18) O ratios were measured as 86.8 super(+3.9) sub(-3.7) ( delta\rm C} = 30 ) and 479 super(+29) sub(-28) ( delta\rm O} = 41 ), respectively. These values may require current theories of solar system formation, such as the CO self- shielding hypothesis, 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. Whilst the line asymmetries (bisectors) were reasonably well reproduced, line strengths predicted on the basis of C and O abundances from other diagnostics were weaker than observed. 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 4000 K. This shortcoming of the 3D model atmosphere is not surprising, given that it was never intended to properly describe such high layers.
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