3D hydrodynamical model atmospheres of metal-poor stars: Evidence for a low primordial Li abundance

TL;DR

This study uses 3D hydrodynamical models to analyze metal-poor stars, revealing that previous estimates of primordial lithium abundance may have been overestimated due to simplified 1D models.

Contribution

The paper introduces realistic 3D hydrodynamical simulations of metal-poor stars, showing significant differences from traditional 1D models in estimating lithium abundance.

Findings

Primordial Li abundance may be overestimated by 0.2-0.35 dex using 1D models.

3D models reveal steeper temperature gradients affecting spectral lines.

Low atmospheric temperatures due to adiabatic cooling influence spectral analysis.

Abstract

Realistic 3-dimensional (3D), radiative hydrodynamical surface convection simulations of the metal-poor halo stars HD 140283 and HD 84937 have been performed. Due to the dominance of adiabatic cooling over radiative heating very low atmospheric temperatures are encountered. The lack of spectral lines in these metal-poor stars thus causes much steeper temperature gradients than in classical 1D hydrostatic model atmospheres where the temperature of the optically thin layers is determined by radiative equilibrium. The modified atmospheric structures cause changes in the emergent stellar spectra. In particular, the primordial Li abundances may have been overestimated by 0.2-0.35 dex with 1D model atmospheres. However, we caution that our result assumes local thermodynamic equilibrium (LTE), while the steep temperature gradients may be prone to e.g. over-ionization.