A Bayesian multiband fitting technique that identifies unresolved main-sequence binaries in the Pleiades open cluster from Gaia DR3 and 2MASS photometry. An empirical single-star photometric model is calibrated against the PARSEC isochrone, then each of 1154 kinematically selected members receives a posterior probability density over primary mass and mass ratio q, detectable down to the model's minimum stellar mass. Stacking the posteriors yields a binary fraction of 0.34 plus or minus 0.02 and a three-segment power-law mass-ratio distribution - a fiducial exponent of minus 1.0 over 0.3 < q < 0.8 with a deficit at low q and an excess at high q - interpreted through primordial binary formation, dynamical interactions, and the mass-dependent detection limit.
Accurate determination of binary fractions ($f_{\rm b}$) and mass ratio ($q$) distributions is crucial for understanding the dynamical evolution of open clusters. We present an improved multiband fit…