Stellar dynamo models with prominent surface toroidal fields

TL;DR

This paper demonstrates that assuming a harmonic coronal field allows stellar dynamo models to produce prominent surface toroidal magnetic fields, aligning with recent observations of solar-type stars.

Contribution

It introduces a novel approach by assuming a harmonic coronal field, enabling standard mean-field dynamo models to generate observed surface toroidal fields.

Findings

Harmonic coronal field assumption supports toroidal surface fields.

Explains increased toroidal energy in fast rotating stars.

Supports alpha-omega dynamo mechanism for observed fields.

Abstract

Recent spectro-polarimetric observations of solar-type stars have shown the presence of photospheric magnetic fields with a predominant toroidal component. If the external field is assumed to be current-free it is impossible to explain these observations within the framework of standard mean-field dynamo theory. In this work it will be shown that if the coronal field of these stars is assumed to be harmonic, the underlying stellar dynamo mechanism can support photospheric magnetic fields with a prominent toroidal component even in the presence of axisymmetric magnetic topologies. In particular it is argued that the observed increase in the toroidal energy in low mass fast rotating stars can be naturally explained with an underlying $\alpha\Omega$ mechanism.