Small-scale dynamo in cool main sequence stars. II. The effect of metallicity

TL;DR

This study uses 3D magneto-convection simulations to explore how metallicity influences small-scale turbulent magnetic fields in stars similar to the Sun, revealing that lower metallicity enhances magnetic field strength and alters subsurface and surface dynamics.

Contribution

It extends small-scale dynamo simulations to stars with varying metallicity, showing metallicity's impact on magnetic field strength and stellar surface flows.

Findings

Lower metallicity leads to stronger magnetic fields in the convection zone.

Magnetic fields significantly influence subsurface dynamics and photospheric flow velocities.

Vertical magnetic field strength varies with metallicity, from 64G at M/H=0.5 to 85G at M/H=-1.0.

Abstract

All cool main sequence stars including our Sun are thought to have magnetic fields. Observations of the Sun revealed that even in quiet regions small-scale turbulent magnetic fields are present. Simulations further showed that such magnetic fields affect the subsurface and photospheric structure, and thus the radiative transfer and emergent flux. Since small-scale turbulent magnetic fields on other stars cannot be directly observed, it is imperative to study their effects on the near surface layers numerically. Until recently comprehensive three-dimensional simulations capturing the effect of small-scale turbulent magnetic fields only exists for the solar case. A series of investigations extending SSD simulations for other stars has been started. Here we aim to examine small-scale turbulent magnetic fields in stars of solar effective temperature but different metallicity. We investigate the properties of three-dimensional simulations of the magneto-convection in boxes covering the upper convection zone and photosphere carried out with the MURaM code for metallicity values of $ \rm M/H = \{-1.0, 0.0, 0.5\}$ with and without a small-scale-dynamo. We find that small-scale turbulent magnetic fields enhanced by a small-scale turbulent dynamo noticeably affect the subsurface dynamics and significantly change the flow velocities in the photosphere. Moreover, significantly stronger magnetic field strengths are present in the convection zone for low metallicity. Whereas, at the optical surface the averaged vertical magnetic field ranges from 64G for M/H = 0.5 to 85G for M/H = -1.0.