(B − K), B diagram of the confirmed O-type stars in Cygnus OB2 within the 1 deg. radius area adopted by Comerón& Pasquali (2012). Blue dots indicate stars previously known, and red dots represent the new ones confirmed in this work. The upper left vertical line shows the position of the unreddened main sequence based on intrinsic magnitudes from Martins & Plez (2006) at a distance modulus DM = 10.8 mag. The dash-dotted lines represent the locus expected for different spectral type stars using the reddening law of Wright et al. (2015) with R_V = 2.91. The solid line marks the limits imposed by the selection criteria at magnitudes B ≤ 16 mag, Ks < 9 mag. Vertical dotted lines indicate (B − K) color bins.