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

TL;DR

This paper uses 3D hydrodynamical models to study spectral line formation in red giants, revealing significant abundance corrections compared to traditional 1D models and discussing LTE departures.

Contribution

It introduces 3D hydrodynamical simulations for red giant atmospheres to improve spectral line and abundance analyses over 1D models.

Findings

Large negative 3D-1D LTE abundance corrections (-0.5 to -1 dex) for certain lines.

Significant impact of 3D models on elemental abundance determinations.

Discussion of LTE departures in neutral iron line formation.

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.