HR diagrams of OB stars in Cygnus OB2 assuming a DM = 10.8 mag. Known OB stars from Comerón & Pasquali (2012) are also included to complete the sample. Black and orange dots indicate the already known and new OB-type stars respectively. Blue crosses indicate those new stars classified as possible SB2 stars. Top left hand panel: isochrones (dotted lines) and evolutionary stellar tracks (solid lines) for non-rotating models from Ekström et al. (2012). Top right handpanel: isochrones (dotted lines) and evolutionary stellar tracks (solid lines) for rotating models (V/V_c = 0.4) from Ekström et al. (2012) . Bottom left hand panel: isochrones (dotted lines) and evolutionary stellar tracks (solid lines) for non-rotating models from Brott et al. (2011). Bottom right hand panel: isochrones (dotted lines) and evolutionary stellar tracks (solid lines) for rotating models (V_i = 330 km s⁻¹) from Brott et al. (2011).