Top panel: Distributions of OB star masses,  M_OB, in OB+cc binaries. The types of compact objects are colour-coded (BH: black, NS: brown), and the shaded area is related to the OBe feature. The OB+BH binaries formed from CHE are plotted with purple. The number in the legends is the predicted number of OBe stars and normal OB stars, e.g. ‘Black hole: 170+41’ means 170 BH+OBe binaries and 41 BH+OB binaries. The in-layer plot in the top panel shows the distribution in the range 30 - 100 M_⊙ with bin width of 10 M_⊙, while the main plot is produced in 6 - 30 M_⊙ with bin width of 2 M_⊙. The left panel is the distribution of the total population, which is disentangled into Case A systems and Case B systems in the right upper and lower panel, respectively. Middle panel: Distributions of BH masses. Bottom panel: Distributions of mass ratios of OB+cc binaries.