On the origin of the dichotomy of stellar activity cycles

TL;DR

This study identifies two distinct relationships between stellar rotation and activity cycle frequency, suggesting that stellar metallicity influences the magnetic cycle behavior, with implications for understanding stellar magnetic activity.

Contribution

Introduces a Bayesian classification method revealing two different scaling laws in stellar activity cycles linked to metallicity differences.

Findings

Two distinct scaling laws in the $ ext{log}_{10} \, ext{omega}_ ext{cyc}$ -- $ ext{log}_{10} \, ext{Omega}$ plane.

Stars with higher metallicity show decreasing cycle frequency with rotation, while less metallic stars show the opposite.

No significant difference in chromospheric activity indicators between the two groups.

Abstract

The presence of possible correlations between stellar rotation rate $\Omega$ and the frequency of the activity cycle $\omega_\mathrm{cyc}$ is still much debated. We implement a new Bayesian classification algorithm based on a simultaneous regression analysis of multiple scaling laws and we demonstrate the existence of two different scalings in the $\log_{10} \omega_\mathrm{cyc}$ -- $\log_{10} \Omega$ plane for an extended Mt.~Wilson sample of 67 stars. Thanks to metallicity measurements obtained from both ESA Gaia and high-resolution spectroscopy, we argue that the origin of this dichotomy is likely related to the chemical composition: stars whose magnetic cycle frequency increases with rotation rate are less metallic than stars whose magnetic cycle frequency decreases with stellar rotation rates. On the contrary, no clear difference in chromospheric magnetic activity indicators characterizes the two branches.