Stellar Differential Rotation and Coronal Timescales

TL;DR

This study models how stellar surface differential rotation influences the formation and lifetime of magnetic flux ropes, revealing that higher differential rotation leads to shorter flux rope lifetimes and more dynamic coronae.

Contribution

It introduces a combined model of magnetic flux transport and magnetofrictional techniques to quantify the impact of differential rotation on coronal magnetic structures.

Findings

Increased differential rotation decreases flux rope formation time.

Flux rope lifetime is proportional to the stellar lap time.

Stars with high differential rotation have very short-lived flux ropes.

Abstract

We investigate the timescales of evolution of stellar coronae in response to surface differential rotation and diffusion. To quantify this we study both the formation time and lifetime of a magnetic flux rope in a decaying bipolar active region. We apply a magnetic flux transport model to prescribe the evolution of the stellar photospheric field, and use this to drive the evolution of the coronal magnetic field via a magnetofrictional technique. Increasing the differential rotation (i.e. decreasing the equator-pole lap time) decreases the flux rope formation time. We find that the formation time is dependent upon the geometric mean of the lap time and the surface diffusion timescale. In contrast, the lifetime of flux ropes are proportional to the lap time. With this, flux ropes on stars with a differential rotation of more than eight times the solar value have a lifetime of less than two days. As a consequence, we propose that features such as solar-like quiescent prominences may not be easily observable on such stars, as the lifetimes of the flux ropes which host the cool plasma are very short. We conclude that such high differential rotation stars may have very dynamical coronae.