A new spin on age-rotation-activity relations and the evolution of magnetic cycles

<p>The Kepler mission dramatically changed our understanding of how rotation and magnetism evolve in sun-like stars. Rotation in the open clusters with ages up to 2.5 Gyr agreed with previous expectations, but field stars with asteroseismic ages revealed a very different behavior. Beyond middle age, the angular momentum of stars no longer appeared to decrease over time, possibly due to a shutdown of magnetic braking. Ground-based spectroscopy of the older stars revealed that chromospheric activity continues to decrease with age, even while the rotation period remains constant. For stars with known activity cycles, this transition appears to be accompanied by a gradual lengthening of the stellar cycle before it eventually becomes undetectable or disappears entirely. The TESS mission will soon provide new tests of this scenario, by yielding asteroseismic masses and ages for stars observed for decades by the Mount Wilson survey. I will review the evidence for this new theory of magnetic evolution, and discuss future observational tests with the potential to radically transform age-rotation-activity relations.