Stellar Characterization and a Chromospheric Activity Analysis of a K2 Sample of Planet-Hosting Stars

Effective temperatures, surface gravities, and iron abundances were derived for 109 stars observed by the K2 mission using equivalent width measurements of Fe I and Fe II lines. Calculations were carried out in LTE using Kurucz model atmospheres. Stellar masses and radii were derived by combining the stellar parameters with Gaia DR3 parallaxes, V magnitudes, and isochrones. The derived stellar and planetary radii have median internal precision of 1.8% and 2.3%, respectively. The radius gap near Rplanet ≈ 1.9 R⊕ was detected in this K2 sample. Chromospheric activity was measured from the Ca II H and K lines using the S-index; values of log R′HK were investigated as a function of stellar rotational period (Prot) and we found that chromospheric activity decreases with increasing Prot, although there is a large scatter in log R′HK (~0.5) for a given Prot. Activity levels in this sample reveal a paucity of F and G dwarfs with intermediate activity levels (Vaughan-Preston gap). The effect that stellar activity might have on the derivation of stellar parameters was investigated by including magnetically sensitive Fe I lines in the analysis and we find no significant differences between parameters with and without magnetically sensitive lines, although the more active stars (log R′HK > -5.0) exhibit a larger scatter in the differences in Teff and [Fe/H].