Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-12-10
Astron.J.135:785-795,2008
Astronomy and Astrophysics
Astrophysics
10 pages, 10 figures. Accepted for publication in AJ
Scientific paper
10.1088/0004-6256/135/3/785
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 H-alpha emission) as a function of vertical distance from the Galactic Plane. The magnitude and slope of this effect varies as a function of spectral type. Using simple 1-D 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, 3-D space motions and mean properties as a function of spectral type for the SDSS DR5 low-mass star sample.
Bochanski John J.
Covey Kevin R.
Dhital Saurav
Hawley Suzanne L.
Hilton Eric J.
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