3D Stagger model atmospheres with FreeEOS I. Exploring the impact of microphysics on the Sun

TL;DR

This paper introduces a new 3D stellar atmosphere model using FreeEOS and Blue opacity, validated against solar observations, enabling studies of stars with unusual chemical compositions.

Contribution

The authors implement FreeEOS and Blue opacity into the Stagger code, creating a versatile 3D model applicable to stars with diverse chemical abundances.

Findings

Model accurately reproduces solar flux spectrum and limb variation.

Mean stratification aligns with previous Stagger solar models.

Model successfully matches observed hydrogen line profiles.

Abstract

Three-dimensional radiation-hydrodynamics (3D RHD) simulations of stellar surface convection provide valuable insights into many problems in solar and stellar physics. However, almost all 3D near-surface convection simulations to date are based on solar-scaled chemical compositions, which limit their application on stars with peculiar abundance patterns. To overcome this difficulty, we implement the robust and widely-used FreeEOS equation of state and our Blue opacity package into the Stagger 3D radiation-magnetohydrodynamics code. We present a new 3D RHD model of the solar atmosphere, and demonstrate that the mean stratification as well as the distributions of key physical quantities are in good agreement with those of the latest Stagger solar model atmosphere. The new model is further validated by comparing against solar observations. The new model atmospheres reproduce the observed flux spectrum, continuum centre-to-limb variation, and hydrogen line profiles at a satisfactory level, thereby confirming the realism of the model and the underlying input physics. These implementations open the prospect for studying other stars with different $\alpha$-element abundance, carbon-enhanced metal-poor stars and population II stars with peculiar chemical compositions using 3D Stagger model atmospheres.