[Paper Review] The solar photospheric abundance of carbon.Analysis of atomic carbon lines with the CO5BOLD solar model

E. Caffau, H.‐G. Ludwig+6 more|University of Groningen research database (University of Groningen / Centre for Information Technology)|Feb 12, 2010

Solar and Space Plasma DynamicsPhysics and Astronomy39 references56 citations

TL;DR

This study re-evaluates the solar photospheric carbon abundance using the CO5BOLD 3D hydrodynamical solar model and non-local thermodynamic equilibrium (NLTE) corrections via the Kiel code. It derives A(C) = 8.50 ± 0.06, which is ~0.1 dex higher than previous 3D analyses and brings the solar metallicity (Z = 0.0154) into better agreement with helioseismic constraints.

ABSTRACT

The use of hydrodynamical simulations, the selection of atomic data, and the computation of deviations from local thermodynamical equilibrium for the analysis of the solar spectra have implied a downward revision of the solar metallicity. We are in the process of using the latest simulations computed with the CO5BOLD code to reassess the solar chemical composition. We determine the solar photospheric carbon abundance by using a radiation-hydrodynamical CO5BOLD model, and compute the departures from local thermodynamical equilibrium by using the Kiel code. We measure equivalent widths of atomic CI lines on high resolution, high signal-to-noise ratio solar atlases. Deviations from local thermodynamic equilibrium are computed in 1D with the Kiel code. Our recommended value for the solar carbon abundance, relies on 98 independent measurements of observed lines and is A(C)=8.50+-0.06, the quoted error is the sum of statistical and systematic error. Combined with our recent results for the solar oxygen and nitrogen abundances this implies a solar metallicity of Z=0.0154 and Z/X=0.0211. Our analysis implies a solar carbon abundance which is about 0.1 dex higher than what was found in previous analysis based on different 3D hydrodynamical computations. The difference is partly driven by our equivalent width measurements (we measure, on average, larger equivalent widths with respect to the other work based on a 3D model), in part it is likely due to the different properties of the hydrodynamical simulations and the spectrum synthesis code. The solar metallicity we obtain from the CO5BOLD analyses is in slightly better agreement with the constraints of helioseismology than the previous 3D abundance results. (Abridged)

Motivation & Objective

• To reassess the solar photospheric carbon abundance using state-of-the-art 3D hydrodynamical simulations and NLTE corrections.
• To resolve discrepancies between spectroscopic solar abundances and helioseismic constraints, particularly regarding solar metallicity.
• To evaluate the impact of updated hydrodynamical models (CO5BOLD) and improved atomic data on carbon abundance determinations.
• To quantify uncertainties from hydrogen collisional damping treatments (S_H = 1/3) and line selection in the analysis.
• To improve consistency between spectroscopic abundance determinations and helioseismic observations of the Sun.

Proposed method

• Measured equivalent widths of 98 independent C i lines from high-resolution, high signal-to-noise solar atlases of disc-centre intensity and integrated disc flux.
• Performed spectral synthesis using the CO5BOLD 3D hydrodynamical solar model to simulate the solar atmosphere and radiative transfer.
• Computed non-LTE corrections using the Kiel code with the 1D average temperature structure from the CO5BOLD simulation as a background model.
• Applied a consistent treatment of hydrogen collisional damping with S_H = 1/3, the preferred value from prior solar abundance studies.
• Combined statistical and systematic error estimates, with the latter dominated by uncertainty in hydrogen collision efficiency.
• Used the NIST database and supplementary sources (Bièmont et al. 1993; Asplund et al. 2005a) for accurate transition probabilities (log gf).

Experimental results

Research questions

• RQ1 What is the solar photospheric carbon abundance when derived using the CO5BOLD 3D hydrodynamical model and NLTE corrections?
• RQ2 How does the new carbon abundance compare to previous 3D-based determinations and to the classical value of A(C) = 8.52 ± 0.06?
• RQ3 To what extent does the CO5BOLD model improve agreement with helioseismic constraints compared to earlier 3D models?
• RQ4 How significant are the differences in abundance results due to variations in hydrodynamical models versus line selection and NLTE treatment?
• RQ5 What is the impact of the hydrogen collisional damping parameter S_H on the final carbon abundance determination?

Key findings

• The recommended solar carbon abundance is A(C) = 8.50 ± 0.06, with the error being the linear sum of statistical (0.02 dex) and systematic (0.04 dex) components.
• This value is approximately 0.1 dex higher than previous 3D-based determinations, such as those by Asplund et al. (2005a), and closer to the classical value of 8.52 ± 0.06.
• The solar metallicity derived from this carbon abundance, combined with recent oxygen and nitrogen abundances, is Z = 0.0154 and Z/X = 0.0211, which is higher than the Asplund et al. (2005b) value of Z = 0.0122.
• The improved agreement with helioseismic constraints suggests that the CO5BOLD model and this abundance determination better reproduce the Sun’s internal structure.
• The difference in abundance results between this work and earlier 3D analyses is partly due to larger equivalent width measurements and partly due to differences in the hydrodynamical models and spectrum synthesis codes.
• The uncertainty in hydrogen collisional damping (S_H) contributes only ~0.08 dex to the total error, indicating robustness of the result across plausible S_H values.