On the Evolution of Angular Momentum, Magnetic Activity and Mass Loss Rate of Late Type Main Sequence Stars

With the best data, I find that nearly all 0.5 to 1.2 M_⊙ main sequence stars converge to a single rotational mass-dependent sequence after 750 Myr; when M > 0.8 M_⊙, most of them converge in ≈ 120 Myr. If stars rotate as rigid bodies, most have angular momenta within clear bounds. The lower bound defines a terminal main sequence rotational isochrone, the upper one coincides with slow rotators from the Pleiades; stars from Praesepe delineate a third one. Mass dependent exponential relationships between angular momentum and age are determined. Age estimates based on the angular momentum are acceptable for stars older than 750 Myr and with M > 0.6 - 0.7 M_⊙. The Rossby number indicates that the Parker dynamo may cease early on in stars with M/M_⊙ ≥ 1.1. An empirical formula and a model for the torque, and a relation between rotational period and magnetic field, lead to a formula for the evolution of the mass loss rate; the present solar rate is near a minimum and was about five times larger when life on Earth started.