The Solar Neighborhood LV: Spectral Characterization of an Equatorial Sample of 580 K Dwarfs

We present a spectroscopic characterization of 580 K dwarfs within 33 pc, observed with the CHIRON echelle spectrograph ( R = 80,000) on the SMARTS 1.5 m telescope. This volume-limited sample is part of the RKSTAR survey of ∼4400 K dwarf primaries within 50 pc. Using Empirical SpecMatch and the diagnostic lines H α (6562.8 Å) and Li I (6707.8 Å), we derive stellar properties, activity status, and age indicators calibrated against 35 benchmark K dwarfs with ages from 20 Myr to 5 Gyr. We find that 7.4% (43 stars) exhibit signatures of youth and/or chromospheric activity: 19 stars show lithium absorption indicating ages <1 Gyr, and 36 display H α emission. Kinematic analysis using BANYAN Σ identifies eight additional young stars through membership in the AB Doradus moving group and the Hyades cluster, bringing the total young/active population to 8.8% (51 stars). Stellar parameters span 3600–5500 K in T eff , −0.60 to +0.55 dex in [Fe/H], and <10 to >25 km s −1 in v sin i . A metal-poor population ([Fe/H] ≤ −0.50 dex) comprises 4% of the sample. Galactic kinematics place 80% in the thin disk and 18.4% in the thick disk, with one halo member (HD 134439). Young and active stars are predominantly thin disk members, with two thick-disk exceptions. Cross-matching with NASA’s Exoplanet Archive reveals only 7.5% (44 stars) host confirmed planets as of 2025 July. Our results identify 529 mature, inactive K dwarfs as prime targets for terrestrial planet searches, providing a crucial resource for exoplanet habitability studies in the solar neighborhood.