Explaining the coexistence of large-scale and small-scale magnetic fields in fully convective stars

TL;DR

This paper presents a 3D magnetohydrodynamic model demonstrating how fully convective stars generate both large-scale and small-scale magnetic fields through a distributed dynamo mechanism, aligning with observations.

Contribution

The study introduces a self-consistent 3D model that reproduces the observed magnetic field structures in fully convective stars, highlighting a different dynamo process from the solar one.

Findings

The model produces a dipole-dominated large-scale magnetic field.

Synthetic spectropolarimetric data recover most of the large-scale field.

The model reproduces both the morphology and magnitude of observed magnetic fields.

Abstract

Despite the lack of a shear-rich tachocline region low-mass fully convective stars are capable of generating strong magnetic fields, indicating that a dynamo mechanism fundamentally different from the solar dynamo is at work in these objects. We present a self-consistent three dimensional model of magnetic field generation in low-mass fully convective stars. The model utilizes the anelastic magnetohydrodynamic equations to simulate compressible convection in a rotating sphere. A distributed dynamo working in the model spontaneously produces a dipole-dominated surface magnetic field of the observed strength. The interaction of this field with the turbulent convection in outer layers shreds it, producing small-scale fields that carry most of the magnetic flux. The Zeeman-Doppler-Imaging technique applied to synthetic spectropolarimetric data based on our model recovers most of the large-scale field. Our model simultaneously reproduces the morphology and magnitude of the large-scale field as well as the magnitude of the small-scale field observed on low-mass fully convective stars.