SDSS J022804.44-010500.5 , the SIMBAD biblio

We present a spectroscopic analysis of over 38,000 low-mass stars from the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5). Analysis of this unprecedentedly large sample confirms the previously detected decrease in the fraction of magnetically active stars (as traced by Hα emission) as a function of the vertical distance from the Galactic plane. The magnitude and slope of this effect vary as a function of spectral type. Using simple 1D dynamical models, we demonstrate that the drop in activity fraction can be explained by thin-disk dynamical heating and a rapid decrease in magnetic activity. The timescale for this rapid activity decrease changes according to the spectral type. By comparing our data to the simulations, we calibrate the age-activity relation at each M dwarf spectral type. We also present evidence for a possible decrease in the metallicity as a function of height above the Galactic plane. In addition to our activity analysis, we provide line measurements, molecular band indices, colors, radial velocities, 3D space motions, and mean properties as a function of spectral type for the SDSS DR5 low-mass star sample.