Cool Stars 14 - Submitted Abstract # 18
This version created on 05 October 2006

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


Andrew West, U.C. Berkeley
Suzanne Hawley, University of Washington
John Bochanski, University of Washington
Kevin Covey, CfA
Kelle Cruz, AMNH

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.

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