The true stellar parameters of the Kepler target list

TL;DR

This study uses synthetic models to evaluate the accuracy of stellar parameters derived by Kepler's classification method, revealing systematic differences and implications for exoplanet radius estimates.

Contribution

It provides a detailed comparison between true and derived stellar parameters in the Kepler sample, highlighting systematic biases and effects of binary star inclusion.

Findings

Median temperature difference of +500K for main-sequence stars

Surface gravity is underestimated by -0.2 dex on average

Binary fraction remains consistent after target selection

Abstract

Using population synthesis tools we create a synthetic Kepler Input Catalogue (KIC) and subject it to the Kepler Stellar Classification Program (SCP) method for determining stellar parameters such as the effective temperature Teff and surface gravity g. We achieve a satisfactory match between the synthetic KIC and the real KIC in the log g vs log Teff diagram, while there is a significant difference between the actual physical stellar parameters and those derived by the SCP of the stars in the synthetic sample. We find a median difference \Delta Teff=+500K and \Delta log g =-0.2dex for main-sequence stars, and \Delta Teff=+50K and \Delta log g =-0.5dex for giants, although there is a large variation across parameter space. For a MS star the median difference in g would equate to a ~3% increase in stellar radius and a consequent ~3% overestimate of the radius for any transiting exoplanet. We find no significant difference between \Delta Teff and \Delta log g for single stars and the primary star in a binary system. We also re-created the Kepler target selection method and found that the binary fraction is unchanged by the target selection. Binaries are selected in similar proportions to single star systems; the fraction of MS dwarfs in the sample increases from about 75% to 80%, and the giant star fraction decreases from 25% to 20%.