Dynamical coupling of a mean-field dynamo and its wind: Feedback loop over a stellar activity cycle

TL;DR

This paper models the feedback loop between a star's internal magnetic dynamo and its wind, revealing how their interaction influences stellar activity cycles and magnetic field configurations.

Contribution

It introduces a coupled 2.5D numerical model combining a mean-field dynamo with a stellar wind, highlighting the impact of feedback on magnetic symmetry and wind variability.

Findings

Feedback modifies dynamo symmetry, favoring quadrupolar modes.

Coronal structure varies with magnetic activity cycle.

Wind feedback influences dynamo mode dominance.

Abstract

We focus on the connection between the internal dynamo magnetic field and the stellar wind. If the star has a cyclic dynamo, the modulations of the magnetic field can affect the wind, which in turn can back-react on the boundary conditions of the star, creating a feedback loop. We have developed a 2.5-dimensional numerical set-up to model this essential coupling. We have implemented an alpha-Omega mean-field dynamo in the PLUTO code, and then coupled it to a spherical polytropic wind model via an interface composed of four grid layers with dedicated boundary conditions. We present here a dynamo model close to a young Sun with cyclic magnetic activity. First we show how this model allows to track the influence of the dynamo activity on the corona by displaying the correlation between the activity cycle, the coronal structure and the time evolution of integrated quantities. Then we add the feedback of the wind on the dynamo and discuss the changes observed in the dynamo symmetry and the wind variations. We explain these changes in terms of dynamo modes : in this parameter regime, the feedback loop leads to a coupling between the dynamo families via a preferred growth of the quadrupolar mode. We also study our interface in terms of magnetic helicity, and show that it leads to a small injection in the dynamo. This model confirms the importance of coupling physically internal and external stellar layers, as it has a direct impact on both the dynamo and the wind.