Constraining the Age-Activity Relation for Cool Stars: The SDSS DR5 Low-Mass Star Spectroscopic Sample

TL;DR

This study analyzes over 38,000 low-mass stars from SDSS DR5 to understand how magnetic activity decreases with age and height above the Galactic Plane, calibrating the age-activity relation across spectral types.

Contribution

It provides the first large-scale calibration of the age-activity relation for low-mass stars using SDSS data and dynamical models.

Findings

Magnetic activity decreases with height above the Galactic Plane.

The activity decline timescale varies with spectral type.

Evidence suggests metallicity decreases with height.

Abstract

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.