Dependence of a1 and a2 on both ζ and d. The size of the symbols depicts the value of the final mass of the BH. Top panel: a2 as a function ζ for initial d* = 2, d* = 3 and d* = 5. Bottom panel: a1 as a function ζ for initial d* = 2, d* = 3 and d* = 5, under the assumption that M1 had no spin before the final SN explosion a1(t = 0) = 0.