Effects of turbulent pumping on stellar activity cycles

TL;DR

This study investigates how turbulent pumping influences stellar magnetic activity cycles, demonstrating that it can explain observed trends with stellar rotation and dominate over meridional circulation at high rotation rates, leading to different cycle behaviors.

Contribution

The paper introduces turbulent pumping as a significant mechanism in stellar dynamo models, showing it can reproduce observed stellar activity trends and dominate at high rotation rates.

Findings

Turbulent pumping can reproduce observed stellar cycle trends.

At high rotation rates, turbulent pumping dominates over meridional circulation.

Different activity cycle regimes emerge when turbulent pumping is dominant.

Abstract

Stellar magnetic activity of solar like stars is thought to be due to an internal dynamo. While the Sun has been the subject of intense research for refining dynamo models, observations of magnetic cyclic activity in solar type stars have become more and more available, opening a new path to understand the underlying physics behind stellar cycles. For instance, it is key to understand how stellar rotation rate influences magnetic cycle period $\Pcyc$. Recent numerical simulations of advection-dominated Babcock Leighton models have demonstrated that it is difficult to explain this observed trend given a) the strong influence of the cycle period to the meridional circulation amplitude and b) the fact that 3D models indicate that meridional flows become weaker as the rotation rate increases. In this paper, we introduce the turbulent pumping mechanism as another advective process capable also of transporting the magnetic fields. We found that this model is now able to reproduce the observations under the assumption that this effect increases as $\Omega^2$. The turbulent pumping becomes indeed another major player able to circumvent the meridional circulation. However, for high rotation rates ($\Omega \simeq 5 \Omega_\odot$), its effects dominate those of the meridional circulation, entering a new class of regime dominated by the advection of turbulent pumping and thus leading to a cyclic activity qualitatively different from that of the sun.