Using Galactic Dynamics to Infer the Evolution of Magnetic Activity in Cool Stars

Speaker: Andrew West

We present a spectroscopic study and dynamical analysis of more than 25000 M and L-type dwarfs from the SDSS Data Release 5. We find that the fraction of magnetically active stars (as traced by H-alpha) decreases as a function of vertical distance from the Galactic Plane. The magnitude and slope of this effect vary as a function of spectral type. We show that the luminosity of the H-alpha emission for a given spectral type may also decrease with distance. Using space motions for ~15000 of the stars and a simple dynamical model, we demonstrate that the observed drop in activity fraction can be explained by thin disk dynamical heating and a rapid decrease in magnetic activity with a timescale that changes according to spectral type. By comparing our data to the simulations, we calibrate the age-activity relation at each spectral type.