Procedure for estimating the fraction of binaries among upper MS stars with masses of 0.36−0.75 M_⊙. This figure reproduces the m_F814W vs. m_F606W − m_F814W CMD of Fig. 1. The candidate binaries are represented with yellow stars and the remaining stars with small gray circles. The solid green line represents the MS fiducial line, while solid and dashed red lines are the fiducial lines of binaries with mass ratios q = 0.5 and q = 1, respectively. The dashed-dotted green and red lines are the MS fiducial line and the fiducial line of binaries with q = 1 shifted by three times the color error. The blue lines mark the locus of binaries where the mass of the primary component corresponds to 0.36 (upper line) and 0.75 M_⊙ (bottom line) and the mass ratio ranges from 0 to 1. In the simulated CMD (right panel), stars located within region B are displayed as gray triangles.