Connecting the large- and the small-scale magnetic fields of solar-like stars

TL;DR

This study links small- and large-scale magnetic fields in solar-like stars through 3D simulations, revealing how stellar parameters influence magnetic topology and matching observed solar-like star fields.

Contribution

It introduces a coupled flux transport and coronal model to analyze magnetic field topologies across scales, connecting simulations with observations.

Findings

Large-scale fields match observed solar-like stars.

Flux emergence rate influences magnetic flux across scales.

Differential rotation affects the poloidal and toroidal field balance.

Abstract

A key question in understanding the observed magnetic field topologies of cool stars is the link between the small- and the large-scale magnetic field and the influence of the stellar parameters on the magnetic field topology. We examine various simulated stars to connect the small-scale with the observable large-scale field. The highly resolved 3D simulations we used couple a flux transport model with a non-potential coronal model using a magnetofrictional technique. The surface magnetic field of these simulations is decomposed into spherical harmonics which enables us to analyse the magnetic field topologies on a wide range of length scales and to filter the large-scale magnetic field for a direct comparison with the observations. We show that the large-scale field of the self-consistent simulations fits the observed solar-like stars and is mainly set up by the global dipolar field and the large-scale properties of the flux pattern, e.g. the averaged latitudinal position of the emerging small-scale field and its global polarity pattern. The stellar parameters flux emergence rate, differential rotation and meridional flow affect the large-scale magnetic field topology. An increased flux emergence rate increases the magnetic flux in all field components and an increased differential rotation increases the toroidal field fraction by decreasing the poloidal field. The meridional flow affects the distribution of the magnetic energy across the spherical harmonic modes.