Our ability to model the shapes and strengths of iron lines in the solar spectrum is a critical test of the accuracy of the solar iron abundance , which sets the absolute zero-point of all stellar metallicities .
We use an extensive 463-level Fe atom with new photoionisation cross-sections for FeI as well as quantum mechanical calculations of collisional excitation and charge transfer with neutral hydrogen ; the latter effectively remove a free parameter that has hampered all previous line formation studies of Fe in non-local thermodynamic equilibrium ( NLTE ) .
For the first time , we use realistic 3D NLTE calculations of Fe for a quantitative comparison to solar observations .
We confront our theoretical line profiles with observations taken at different viewing angles across the solar disk with the Swedish 1-m Solar Telescope .
We find that 3D modelling well reproduces the observed centre-to-limb behaviour of spectral lines overall , but highlight aspects that may require further work , especially cross-sections for inelastic collisions with electrons .
Our inferred solar iron abundance is \log ( \epsilon _ { Fe } ) = 7.48 \pm 0.04 dex .