Stellar activity cycles in a model for magnetic flux generation and transport

TL;DR

This paper models magnetic flux generation and transport in cool stars, combining dynamo theory, flux tube rise, and surface transport, to explain observed stellar activity cycles across different star types.

Contribution

It introduces a comprehensive model integrating dynamo processes, flux emergence, and surface transport, applied to various star types, to explain stellar activity cycles.

Findings

A Sun-like star with 9-day rotation can have a cyclic dynamo with non-cyclic surface activity.

A K1 subgiant star with 2.8-day rotation shows multi-periodic activity similar to observed stars.

The model reproduces diverse stellar activity behaviors by varying stellar parameters.

Abstract

We present results from a model for magnetic flux generation and transport in cool stars and a qualitative comparison of models with observations. The method combines an alpha-omega dynamo at the base of the convection zone, buoyant rise of magnetic flux tubes, and a surface flux transport model. Based on a reference model for the Sun, numerical simulations were carried out for model convection zones of G- and K-type main sequence and subgiant stars. We investigate magnetic cycle properties for stars with different rotation periods, convection zone depths, and dynamo strengths. For a Sun-like star with P_rot=9 d, we find that a cyclic dynamo can underly an apparently non-cyclic, 'flat' surface activity, as observed in some stars. For a subgiant K1 star with P_rot=2.8 d the long-term activity variations resemble the multi-periodic cycles observed in V711 Tau, owing to high-latitude flux emergence, weak transport effects and stochastic processes of flux emergence.