Constraining the Age-Activity Relation for Cool Stars: The Sloan Digital Sky Survey Data Release 5 Low-Mass Star Spectroscopic Sample

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 Hα 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.

Tidal Venuses: Triggering a Climate Catastrophe via Tidal Heating

“…Such stars are very active and emit strongly in the near UV, especially when they are young (e.g., West et al, 2008), but the total flux is still less than that of the present-day Sun (Fleming et al, 1993), and the XUV flux (which drives hydrodynamic escape) is not well known. Thus, we expect a range of t des to exist, especially since the orbit evolves with time due to tides, but choose this value for simplicity.…”

“…The stars are very faint and, moreover, prone to flaring. However, there is a secular decrease in activity as the stars age (West et al, 2008), but the data are still too sparse to allow a satisfactory fit. Recent work connected X-ray sources from space telescopes (e.g., GALEX) and ground-based surveys (e.g., Sloan Digital Sky Survey) and found that older low-mass stars tend to emit about 10 -6 to 10 -3 of their energy in the XUV in quiescence (West, personal communication).…”

Discovery of wide low and very low-mass binary systems using Virtual Observatory tools

“…But we only have measurements of radial velocity for two candidates, 2MASS J13570535+3403459 and 2MASS J09332493+3232033, with values of 64.2 and -12.9 km −1 respectively (errors between 5-10 km −1 ) from West et al (2008). They calculated the Galactic space-velocity components (U, V, W ) using photometric distance values of 179 and 180 pc (quite similar to the ones obtained here), obtaining (-32.5, -5.0, 54.0) and (8.4, 1.9, -5.4).…”

“…The W component is always affected by larger dispersion, so the target may still belong to the young disc area. West et al (2008) calculated vertical distance from the Galactic plane of 146.2 and 188.0 pc that correspond to the thin disc (e.g. Pauli et al 2006).…”

“…Two candidates have spectral classification from literature, 2MASS J13570535+3403459 and 2MASS J09332493+3232033, both classified as M6 by West et al (2008) using the HAMMER stellar spectral-typing facility (Covey et al 2007) on their SDSS spectra. These values are in agreement with our photometric spectral types (M7 and M6.5, respectively).…”