Dynamo modelling for cycle variability and occurrence of grand minima in Sun-like stars: Rotation rate dependence

TL;DR

This study uses flux transport dynamo models to simulate how rotation rate influences cycle variability and grand minima occurrence in Sun-like stars, aligning with observational trends.

Contribution

It introduces the first flux transport dynamo simulations that replicate observed activity patterns across different stellar rotation rates.

Findings

Rapid rotators have irregular cycles with few grand minima.

Slow rotators exhibit smooth cycles with occasional grand minima.

Grand minima duration and frequency increase as rotation slows.

Abstract

Like the solar cycle, stellar activity cycles are also irregular. Observations reveal that rapidly rotating (young) Sun-like stars exhibit a high level of activity with no Maunder-like grand minima and rarely display smooth regular activity cycles. On the other hand, slowly rotating old stars like the Sun have low activity levels and smooth cycles with occasional grand minima. We, for the first time, try to model these observational trends using flux transport dynamo models. Following previous works, we build kinematic dynamo models of one solar mass star with different rotation rates. Differential rotation and meridional circulation are specified with a mean-field hydrodynamic model. We include stochastic fluctuations in the Babcock-Leighton source of the poloidal field to capture the inherent fluctuations in the stellar convection. Based on extensive simulations, we find that rapidly rotating stars produce highly irregular cycles with strong magnetic fields and rarely produce Maunder-like grand minima, whereas the slowly-rotating stars (with a rotation period of 10 days and longer) produce smooth cycles of weaker strength, long-term modulation in the amplitude, and occasional extended grand minima. The average duration and the frequency of grand minima increase with decreasing rotation rate. These results can be understood as the tendency of less supercritical dynamo in slower rotating stars to be more prone to produce extended grand minima