The Revolution Revolution: Magnetic Morphology Driven Spin-down

Observations of young open clusters (OCs) show a bimodal distribution of rotation periods that has been difficult to explain with existing stellar spin-down models. Detailed magnetohydrodynamic (MHD) stellar wind simulations have demonstrated that surface magnetic field morphology has a strong influence on wind-driven angular momentum loss. Observations suggest that faster rotating stars store a larger fraction of their magnetic flux in higher-order multipolar components of the magnetic field. In this work, we present an entirely predictive new model for stellar spin-down that accounts for the stellar surface magnetic field configuration. We show how a magnetic complexity that evolves from complex toward simple configurations as a star spins down can explain the salient features of stellar rotation evolution, including the bimodal distribution of both slow and fast rotators seen in young OCs.

Title inspired by C. L. Davis PhD Thesis Revolution evolution: tracing angular momentum during star and planetary system formation, St. Andrews University.