Abstract

Open clusters, such as the Pleiades, Praesepe, and the Hyades, are critical benchmarks for calibrating stellar properties such as rotation and magnetic activity. As stars approach the main sequence, they contract and spin more rapidly; once they reach the main sequence, they stop contracting and their spin speed decreases. This spin-down is caused by angular momentum lost via stellar winds, but details of stellar wind torques and any internal angular momentum transport are still uncertain. I will discuss recent results constraining the rotation of old, low-mass stars along with young, solar-mass stars. I will show how we can use these clusters and a new, statistically robust fitting method to distinguish between models of stellar rotational evolution.