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 Values of log RHK 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 RHK (~0.5) for a given Pᵣₒₜ. Activity levels in this sample reveal a paucity of F & 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].