Case A mass transfer. The initial binary parameters are M_d = 12   M_⊙ (VUB solid black and ULB red dotted lines), M_d = 7.2   M_⊙ (VUB short dashed green and ULB long-dashed blue line) and P = 4d. The figure shows the evolution as a function of stellar mass of the stellar radius a), the mass transfer rate (b), left axis) and period (b), right axis), the evolutionary path in the HRD of the binary system c) and the time evolution of the mass transfer rate d). In panel d) the transfer time t_transfer is defined as t − 18.4 Myr for the VUB model and t − 29.3 Myr in our case. The final masses are 2.66 M_⊙ and 16.54 M_⊙.