Beyond 1D: spectral line formation with 3D hydrodynamical model atmospheres of red giants

Abstract

We present the results of realistic, 3D, hydrodynamical, simulations of surface convection in red giant stars with varying effective temperatures and metallicities. We use the convection simulations as time-dependent, hydrodynamical, model atmospheres to compute spectral line profiles for a number of ions and molecules under the assumption of local thermodynamic equilibrium (LTE). We compare the results with the predictions of line formation calculations based on 1D, hydrostatic, model stellar atmospheres in order to estimate the impact of 3D models on the derivation of elemental abundances. We find large negative 3D-1D LTE abundance corrections (typically -0.5 to -1 dex) for weak low-excitation lines from molecules and neutral species in the very low metallicity cases. Finally, we discuss the extent of departures from LTE in the case of neutral iron spectral line formation.