Fe/H & radii from blended sp. of simulated binaries

Fitting tools that determine stellar parameters from spectra typically fit for a single star, but we know that up to half of all exoplanet host stars may have one or more companion stars. We use high- resolution spectra of planet host stars in the Kepler field from the California-Kepler Survey to create simulated binaries; we select eight stellar pairs and vary the contribution of the secondary star, then determine stellar parameters with SpecMatch-Emp and compare them to the parameters derived for the primary star alone.

We find that, in most cases, the effective temperature, surface gravity, metallicity, and stellar radius derived from the composite spectrum are within 2-3{sigma} of the values determined from the unblended spectrum, but the deviations depend on the properties of the two stars. Relatively bright companion stars that are similar to the primary star have the largest effect on the derived parameters; in these cases, the stellar radii can be overestimated by up to 60%.