The Mass–Activity Relationships in M and K Dwarfs. I. Stellar Parameters of Our Sample of M and K Dwarfs

Empirical correlations between stellar parameters such as rotation or radius and magnetic activity diagnostics require estimates of the effective temperatures and the stellar radii. The aim of this study is to propose simple methods that can be applied to large samples of stars in order to derive estimates of the stellar parameters. Good empirical correlations between red/infrared colors (e.g., ( R – I ) C ) and effective temperatures have been well established for a long time. The more recent ( R – I ) C color– T eff correlation using the data of Mann et al. (hereafter M15) and Boyajian et al. (hereafter B12) shows that this color can be applied as a temperature estimate for large samples of stars. We find that the mean scatter in T eff relative to the ( R – I ) C – T eff relationship of B12 and M15 data is only ±3 σ = 44.6 K for K dwarfs and ±3 σ = 39.4 K for M dwarfs. These figures are small and show that the ( R – I ) C color can be used as a first-guess effective temperature estimator for K and M dwarfs. We derive effective temperatures for about 1910 K and M dwarfs using the calibration of ( R – I ) C color– T eff from B12 and M15 data. We also compiled T eff and metallicity measurements available in the literature using the VizieR database. We determine T eff for 441 stars with previously unknown effective temperatures. We also identified 21 new spectroscopic binaries and one triple system from our high-resolution spectra.