Unresolved Binaries in the Intermediate Mass Range in the Pleiades Star
  Cluster
  The identification of binary stars of different mass ratios in resolved
stellar populations is a challenging task. We show how the photometric diagram
constructed with the pseudo-colors (H-W2)-W1 vs W2-(BP-K) can be employed to
estimate the binary and multiple star ratios and the distribution of their
component mass ratio $q$ effectively. As an application, we investigate the
Pleiades star cluster in the range of primary component mass between 0.5 and
1.8 $M_{\odot}$. The binary star ratio is found to be between 0.54$\pm$0.11 and
0.70$\pm$0.14. On the other hand, the ratio of systems with multiplicity more
than 2 is between 0.10$\pm$0.00 and 0.14$\pm$0.01. The distribution of the
component mass ratio $q$ has been approximated by a power law with the exponent
between -0.53$\pm$0.10 and -0.63$\pm$0.22. Below 0.5 $M_{\odot}$, we expect a
large number of brown dwarfs among secondary components.
