Core-envelope decoupling drives radial shear dynamos in cool stars

TL;DR

This paper proposes that core-envelope decoupling in cool stars causes radial shear, which enhances magnetic activity and star spots, explaining observed anomalies in stellar rotation and activity evolution.

Contribution

It introduces the concept that core-envelope decoupling drives radial shear dynamos, altering stellar magnetic activity and rotation evolution in cool stars.

Findings

Star spot activity is enhanced in stars with decoupled core and envelope.

Radial shear resulting from core-envelope decoupling explains rotation and activity anomalies.

Interior angular momentum redistribution stalls surface rotational evolution.

Abstract

Differential rotation is thought to be responsible for the dynamo process in stars like our Sun, driving magnetic activity and star spots. We report that star spot measurements in the Praesepe open cluster are strongly enhanced only for stars which depart from standard models of rotational evolution. A decoupling of the spin down history between the core and envelope explains both the activity and rotation anomalies: surface rotational evolution is stalled by interior angular momentum redistribution, and the resultant radial shears enhance star spot activity. These anomalies provide evidence for an evolving front of shear-enhanced activity affecting the magnetic and rotational evolution of cool stars and the high-energy environments of their planetary companions for hundreds of millions to billions of years on the main sequence.