Core-envelope Decoupling Drives Radial Shear Dynamos in Cool Stars

• Published in: Astrophysical journal. Letters Vol. 951; no. 2; p. L49
• Main Authors: Cao, Lyra, Pinsonneault, Marc H., van Saders, Jennifer L.
• Format: Journal Article
• Language: English
• Published: Austin The American Astronomical Society 01-07-2023; IOP Publishing
• Subjects: Angular momentum; Anomalies; Astronomy & Astrophysics; Cool stars; Decoupling; Differential rotation; Evolution; Planetary evolution; Rotating generators; Stars; Starspots; Stellar activity; Stellar evolution; Stellar magnetic fields; Stellar rotation
• ISSN: 2041-8205; 2041-8213
• DOI: 10.3847/2041-8213/acd780

Abstract
Differential rotation is thought to be responsible for the dynamo process in stars like our Sun, driving magnetic activity and starspots. We report that starspot measurements in the Praesepe open cluster are strongly enhanced only for stars that 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 starspot 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.