Title: Non-LTE line formation of Fe in late-type stars IV: Modelling of the solar centre-to-limb variation in 3D,
Abstract: 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(eps(Fe))=7.48+-0.04.