CO core masses M_CO at core collapse as a function of the initial mass M_ini for Case A (panel a), Case B (panel b), and Case C (panel c) accretors. Colours show the accretion fraction f_acc of the models, and single stars are shown in blue squares for comparison in panel a. Panels b and c show the difference in M_CO relative to the corresponding single-star core masses. To guide the eye, data points for f_acc = 0.1 (mostly CSGs) and 2.0 (BSGs) are connected by dashed lines and highlighted.