Migrating Dynamo Waves and Consequences for Stellar Current Sheets

TL;DR

This paper investigates how variations in stellar dynamo waves influence magnetic field structures and current sheet behaviors, revealing that small asymmetries can produce realistic magnetic configurations and that poleward activity propagation can differ markedly from solar patterns.

Contribution

It introduces a model linking dynamo wave propagation with magnetic field structures and current sheets, highlighting the effects of asymmetries and poleward propagation on stellar magnetic phenomena.

Findings

Small asymmetries cause realistic dipole-quadrupole relations.

Poleward propagating activity leads to distinct current sheet behaviors.

Conditions identified for opposite propagation directions of current sheets.

Abstract

We study the relation between stellar dynamo-wave propagation and the structure of the stellar magnetic field. Modeling dynamo waves by the well-known Parker migratory dynamo, we vary the intensity of dynamo drivers in order to obtain activity-wave propagation toward the Equator (as in the solar-activity cycle) or towards the Poles. We match the magnetic field in the dynamo active shell with that in the surrounding stellar material, using a simple dissipativ magnetohydrodynamic system for the transition region. Introducing a weak asymmetry between the stellar hemispheres, we study phase shifts of the dipole, quadrupole, and octupole magnetic components at various distances from the star to demonstrate that several-percent asymmetry in dynamo drivers are sufficient to obtain a realistic relation between solar dipole and quadrupole moments. We study the behavior of the stellar current sheets and show that for the poleward propagating activity it is substantially different from solar ones. In particular, we demonstrate conditions in which the conical current sheets propagate opposite to the solar directions.