Confirmed K2 exoplanet host stars opt. sp.

We derived effective temperatures, surface gravities, and iron and magnesium abundances in local thermodynamic equilibrium by measuring the equivalent widths of Fe I, Fe II, and Mg I lines. Three estimates of stellar masses and radii were obtained via the Stefan-Boltzmann and isochrone methods using the codes PARAM and isochrones.

These were used to derive exoplanetary radii reaching internal precisions of 2.5%, 2.6%, and 6.6%, respectively, and the radius gap was consistently detected near 1.9R_{Earth}_. We measured chromospheric activity from the CaII H and K and H{alpha} lines. Within the low-activity range (logR'_HK_{<}-4.75), stellar activity appears to decrease with increasing planetary radius from super-Earths, sub-Neptunes, sub-Saturns, into the Jupiter regime.