TRACERS OF CHROMOSPHERIC STRUCTURE. I. Ca II H&K EMISSION DISTRIBUTION OF 13,000 F, G, AND K STARS IN SDSS DR7 SPECTROSCOPIC SAMPLE

摘要

We present chromospheric activity index S HK measurements for over 13,000 F, G, and K disk stars with high signal-to-noise ratio (60) spectra in the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) spectroscopic sample. A parameter δS is defined as the difference between S HK and a "zero" emission line fitted by several of the most inactive stars. The S HK indices of subgiant stars tend to be much lower than dwarfs, which provide a way to distinguish dwarfs and giants with relatively low-resolution spectra. Cooler stars are generally more active and display a larger scatter than hotter stars. Stars associated with the thick disk are in general less active than those of the thin disk. The fraction of K dwarfs that are active drops with vertical distance from the Galactic plane. Metallicity affects S HK measurements differently among F, G, and K dwarfs in this sample. Using the open clusters NGC?2420, M67, and NGC?6791 as calibrations, ages of most field stars in this SDSS sample range from 3 to 8?Gyr.