Line formation in solar granulation - I. Fe line shapes, shifts and asymmetries

Realistic ab-initio 3D, radiative-hydrodynamical convection simulations of the solar granulation have been applied to Fe I and Fe II line formation. I n contrast to classical analyses based on hydrostatic ID model atmospheres the procedure contains no adjustable free parameters but the treatment of t he numerical viscosity in the construction of the 3D. timedependent, inhomo geneous model atmosphere and the elemental abundance in the 3D spectral syn thesis. However, the numerical viscosity is introduced purely for numerical stability purposes and is determined from standard hydrodynamical test cas es with no adjustments allowed to improve the agreement with the observatio nal constraints from the solar granulation. The non-thermal line broadening is mainly provided by the Doppler shifts ar ising from the convective flows in the solar photosphere and the solar osci llations. The almost perfect agreement between the predicted temporally and spatially averaged line profiles for weak Fe lines with the observed profi les and the absence of trends in derived abundances with line strengths, se em to imply that the micro- and macroturbulence concepts are obsolete in th ese 3D analyses. Furthermore, the theoretical line asymmetries and shifts s how a very satisfactory agreement with observations with an accuracy of typ ically 50-100 m s(-1) on an absolute velocity scale. The remaining minor di screpancies point to how the convection simulations can be refined further.