(a) Evolution of the donor (orange line) and accretor (blue line) masses as a function of orbital period, P_orb, during binary evolution. The filled point marks the present-day observed configuration. (b) Evolution of the donor (orange line) and accretor (blue line) radii as a function of P_orb. (c) Evolution of the orbital period, P_orb (blue line) and mass ratio, q (orange line) of the system. (d) Evolutionary tracks of the donor (orange line) and accretor (blue line) from the best-fit MESA model in the ﹩\mathrm{log}g﹩–T_eff plane.