3D Stagger model atmospheres with FreeEOS

I. Exploring the impact of microphysics on the Sun

¹ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
e-mail: yixiao.zhou@qq.com
² Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
e-mail: anish.amarsi@physics.uu.se
³ DARK, Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen, Denmark
⁴ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
⁵ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia

Received: 13 March 2023
Accepted: 4 July 2023

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 limits their relevance when applied to 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 comparisons with 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 α-element abundance, carbon-enhanced metal-poor stars, and population II stars with peculiar chemical compositions using 3D Stagger model atmospheres.