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A very high resolution (R=200,000), high signal-to-noise ratio (S/N=340)blue-green spectrum of the very metal-poor ([Fe/H]=-2.6) red giant starHD122563 has been obtained by us at McDonald Observatory. We measure theasymmetries and core wavelengths of a set of unblended FeI lines covering awide range of line strength. Line bisectors exhibit the characteristic C-shapesignature of surface convection (granulation) and they span from about 100 m/sin the strongest FeI features to 800 m/s in the weakest ones. Core wavelengthshifts range from about -100 to -900 m/s, depending on line strength. Ingeneral, larger blueshifts are observed in weaker lines, but there isincreasing scatter with increasing residual flux. Assuming local thermodynamicequilibrium (LTE), we synthesize the same set of spectral lines using astate-of-the-art three-dimensional hydrodynamic simulation for a stellaratmosphere of fundamental parameters similar to those of HD122563. We find goodagreement between model predictions and observations. This allows us to inferan absolute zero-point for the line shifts and radial velocity. Moreover, itindicates that the structure and dynamics of the simulation are realistic, thusproviding support to previous claims of large 3D-LTE corrections, based on thehydrodynamic model used here, to elemental abundances and fundamentalparameters of very metal-poor red giant stars obtained with standard 1D-LTEspectroscopic analyses.

Granulation signatures in the spectrum of the very metal-poor red giant HD122563