Solar-Type Activity: Epochs of Cycle Formation

TL;DR

This paper investigates the formation and evolution of solar-type activity cycles in stars, linking stellar age, rotation, and magnetic fields, and providing insights into the young Sun's activity epoch.

Contribution

It introduces a new analysis connecting coronal activity, stellar rotation, and age, offering estimates for the young Sun's activity epoch and discussing magnetic field roles.

Findings

Cycle duration increases with stellar age and rotation deceleration.

Young Sun's activity properties are characterized for stars around one billion years old.

Magnetic field data support the link between magnetic activity and cycle formation.

Abstract

The diagram of indices of coronal and chromospheric activity allowed us to reveal stars where solar-type activity appears and regular cycles are forming. Using new consideration of a relation between coronal activity and the rotation rate, together with new data on the ages of open clusters, we estimate the age of the young Sun corresponding to the epoch of formation of its cycle. The properties of the activity of this young Sun, with an age slightly older than one billion years, are briefly discussed. An analysis of available data on the long-term regular variability of late-type stars leads to the conclusion that duration of a cycle associated with solar-type activity increases with the deceleration of the stellar rotation; i.e., with age. New data on the magnetic fields of comparatively young G stars and changes in the role of the large-scale and the local magnetic fields in the formation of the activity of the young Sun are discussed. Studies in this area aim to provide observational tests aimed at identifying the conditions for the formation of cyclic activity on stars in the lower part of the main sequence, and test some results of dynamo theory.