We describe the photometric calibration and stellar classification methods used by the Stellar Classification Project ( SCP ) to produce the Kepler Input Catalog ( KIC ) .
The KIC is a catalog containing photometric and physical data for sources in the Kepler Mission field of view ; it is used by the mission to select optimal targets .
Four of the visible-light ( g,r,i,z ) magnitudes used in the KIC are tied to SDSS magnitudes ; the fifth ( D 51 ) is an AB magnitude calibrated to be consistent with Castelli & Kurucz ( 6 ) ( henceforth CK ) model atmosphere fluxes .
We derived atmospheric extinction corrections from hourly observations of secondary standard fields within the Kepler field of view .
For these filters and extinction estimates , repeatability of absolute photometry for stars brighter than magnitude 15 is typically 2 % .
We estimated stellar parameters { T _ { eff } , \log ( g ) , \log ( Z ) , E _ { B - V } } using Bayesian posterior probability maximization to match observed colors to CK stellar atmosphere models .
We applied Bayesian priors describing the distribution of solar-neighborhood stars in the color-magnitude diagram ( CMD ) , in \log ( Z ) , and in height above the galactic plane .
Several comparisons with samples of stars classified by other means indicate that for 4500 K \leq T _ { eff } \leq 6500 K , our classifications are reliable within about \pm 200 K and 0.4 dex in \log ( g ) for dwarfs , with somewhat larger \log ( g ) uncertainties for giants .
It is difficult to assess the reliability of our \log ( Z ) estimates , but there is reason to suspect that it is poor , particularly at extreme T _ { eff } .
Comparisons between the CK models and observed colors are generally satisfactory with some exceptions , notably for stars cooler than 4500 K. Of great importance for the Kepler Mission , for T _ { eff } \leq 5400 K , comparison with asteroseismic results shows that the distinction between main-sequence stars and giants is reliable with about 98 % confidence .
Larger errors in \log ( g ) occur for warmer stars , for which our filter set provides inadequate gravity diagnostics .
The KIC is available through the MAST data archive .