Dynamo Saturation in Rapidly Rotating Solar-Type Stars

TL;DR

This paper investigates how the saturation of magnetic activity in rapidly rotating solar-type stars can be explained by the Babcock-Leighton dynamo mechanism, using models with tilt-angles proportional to rotation rate.

Contribution

It introduces stellar dynamo models with tilt-angles linked to rotation rate, demonstrating magnetic flux saturation and a transition to a new dynamo regime at high rotation speeds.

Findings

Magnetic flux saturates at high rotation rates in the models.

A new dynamo regime emerges with cyclic low-latitude and steady polar activity.

Saturation correlates with tilt-angle approaching ninety degrees.

Abstract

The magnetic activity of solar-type stars generally increases with stellar rotation rate. The increase, however, saturates for fast rotation. The Babcock-Leighton mechanism of stellar dynamos saturates as well when the mean tilt-angle of active regions approaches ninety degrees. Saturation of magnetic activity may be a consequence of this property of the Babcock-Leighton mechanism. Stellar dynamo models with a tilt-angle proportional to the rotation rate are constructed to probe this idea. Two versions of the model - treating the tilt-angles globally and using Joy's law for its latitude dependence - are considered. Both models show a saturation of dynamo-generated magnetic flux at high rotation rates. The model with latitude-dependent tilt-angles also shows a change in dynamo regime in the saturation region. The new regime combines a cyclic dynamo at low latitudes with an (almost) steady polar dynamo.