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Register a new userThe elemental composition of the Sun I. The intermediate mass elements Na to Ca
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The composition of the Sun is an essential piece of reference data for astronomy, cosmology, astroparticle, space and geo-physics. 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 solar photospheric model, which has successfully passed an arsenal of observational diagnostics. To quantify systematic errors, we repeat the analysis with three 1D hydrostatic model atmospheres (MARCS, MISS and Holweger & M{u}ller 1974) and a horizontally and temporally-averaged version of the 3D model ($langle$3D$rangle$). We account for departures from LTE wherever possible. We have scoured the literature for the best transition probabilities, partition functions, hyperfine and other data, and stringently checked all observed profiles for blends. Our final 3D+NLTE abundances are: $logepsilon_{mathrm{Na}}=6.21pm0.04$, $logepsilon_{mathrm{Mg}}=7.59pm0.04$, $logepsilon_{mathrm{Al}}=6.43pm0.04$, $logepsilon_{mathrm{Si}}=7.51pm0.03$, $logepsilon_{mathrm{P}}=5.41pm0.03$, $log epsilon_{mathrm{S}}=7.13pm0.03$, $logepsilon_{mathrm{K}}=5.04pm0.05$ and $logepsilon_{mathrm{Ca}}=6.32pm0.03$. 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. The $langle$3D$rangle$ model returns abundances very similar to the full 3D calculations. This analysis provides a complete description and a slight update of the Na to Ca results presented in Asplund, Grevesse, Sauval & Scott (arXiv:0909.0948), with full details of all lines and input data.
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We benchmark new atomic data against a selection of irradiances obtained from medium-resolution quiet Sun spectra in the EUV, from 60 to 1040 AA. We use as a baseline the irradiances measured during solar minimum on 2008 April 14 by the prototype (PEVE) of the Solar Dynamics Observatory Extreme ultraviolet Variability Experiment (EVE). We take into account some inconsistencies in the PEVE data, using flight EVE data and irradiances we obtained from Solar & Heliospheric Observatory (SoHO) Coronal Diagnostics Spectrometer (CDS) data. We perform a differential emission measure and find overall excellent agreement (to within the accuracy of the observations, about 20%) between predicted and measured irradiances in most cases, although we point out several problems with the currently available ion charge state distributions. We used the photospheric chemical abundances of Asplund et al. (2009). The new atomic data are nearly complete in this spectral range, for medium-resolution irradiance spectra. Finally, we use observations of the active Sun in 1969 to show that also in that case the composition of the solar corona up to 1 MK is nearly photospheric. Variations of a factor of 2 are present for higher-temperature plasma, which is emitted within active regions.These results are in excellent agreement with our previous findings.
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