Initial separation (a_i) versus initial mass of the primary star (M_i, left) and versus initial mass ratio (M_2,i/M_1,i, right) of systems that form SNe Ia through the DD channel in our standard model (Sect. 2). Number density (greyscale) represents the number of systems normalized to the total number of systems forming a SN Ia through the DD channel. Lines show the minimum separation (assuming q = 1) for which the primary fills its Roche lobe at a certain stage of evolution, as indicated. Symbols A–F indicate differences in the evolutionary stage when the primary fills its Roche lobe and in the number of CE phases necessary to evolve to a SN Ia: A = HG, no CE; B = HG, 1 CE (the difference between B₁ and B₂ is based on which of the two stars first forms a WD); C = GB, 1 CE; D = E-AGB, 1 CE; E = TP-AGB, 1 CE; F = TP-AGB, 2 CEs.