Line formation in solar granulation VI. [C I], C I, CH and C2 lines and the photospheric C abundance

TL;DR

This study determines the solar photospheric carbon abundance using advanced 3D hydrodynamical models and multiple spectral diagnostics, achieving consistent results and revealing a lower abundance than earlier 1D model estimates.

Contribution

It provides a new, more accurate measurement of the solar carbon abundance using 3D models and multiple spectral lines, accounting for non-LTE effects.

Findings

Solar carbon abundance is log C = 8.39 +/- 0.05.

3D models yield lower abundance estimates than 1D models.

Consistent results across atomic and molecular diagnostics.

Abstract

The solar photospheric carbon abundance has been determined from [C I], C I, CH vibration-rotation, CH A-X electronic and C2 Swan electronic lines by means of a time-dependent, 3D, hydrodynamical model of the solar atmosphere. Departures from LTE have been considered for the C I lines. These turned out to be of increasing importance for stronger lines and are crucial to remove a trend in LTE abundances with the strengths of the lines. Very gratifying agreement is found among all the atomic and molecular abundance diagnostics in spite of their widely different line formation sensitivities. The mean of the solar carbon abundance based on the four primary abundance indicators ([C I], C I, CH vibration-rotation, C_2 Swan) is log C = 8.39 +/- 0.05, including our best estimate of possible systematic errors. Consistent results also come from the CH electronic lines, which we have relegated to a supporting role due to their sensitivity to the line broadening. The new 3D based solar C abundance is significantly lower than previously estimated in studies using 1D model atmospheres.