Simulated distribution of the population of merging double CO white dwarfs from a single burst of star formation as a function of delay time and total mass of the system. On the left model γα is used for the common envelope parametrisation, on the right model αα (see Sect. 3). The intensity of the grey scale corresponds to the density of objects on a linear scale in units of number of systems per 10⁵ M_⊙. The black line corresponds to a combined mass of 1.4 M_⊙.