Spectral Characterization of a Complete Equatorial Sample of 615 K Dwarfs

Abstract Our study analyzes nearby (within 33 pc) K dwarf stars to determine their stellar properties, activity levels, kinematics, and estimated ages, as part of the RKSTAR (RECONS K Star) Survey encompassing about 5000 K dwarf primaries within 50 pc. Utilizing high-resolution spectra from the CHIRON echelle spectrometer, we established a benchmark set of 35 K dwarfs aged 20 Myr to 5 Gyr, focusing on the H α (6563 Å) and Li I (6707.9 Å) lines. We extended our analysis to 615 K dwarfs within 33 pc and found that about 8% exhibit spectroscopic features characteristic of young or active stars. As expected, Galactic UVW space motions indicate that most of the stars fall into the thin (80%) and thick (20%) disk populations, with a single outlier, HD 134439, which is a known halo star. Additionally, 4% of the stars were identified as metal-poor ([Fe/H] ≤ −0.5 dex). This work identifies 500 inactive and mature K dwarfs as prime targets for detecting terrestrial planets and serves as a vital resource for assessing host star suitability for exoplanet habitability.