The magnetic, basal, and radiative-equilibrium components in Mount Wilson Ca II H + K fluxes

Mount Wilson Ca II H + K flux measurements of cool dwarf stars are analyzed and compared with stellar Mg II h + k fluxes, variability amplitudes, rotation rates, and solar data. It is concluded that the Mount Wilson Ca II H + K fluxes comprise three principal parts: (1) a photospheric contribution in the line wings, (2) a basal chromospheric component that appears to be unrelated to stellar magnetic activity and is, therefore, possibly nonmagnetic in origin, and (3) a chromospheric component which is associated with magnetically active regions and the (quiet and active) network. The basal chromosphere appears to cover the entire surface of magnetically inactive stars. The basal Ca II H + K flux density for solar-type stars equals the average emission observed in the centers of solar supergranulation cells, where the magnetic flux density is small.