Evolution of a_crit and the HZ for three hypothetical equal-mass binaries. The blue shaded region is the HZ; the black curves are the values of a_crit ; the dashed horizontal orange lines are the maximum value of a_crit; and the dashed vertical red lines are the time that a_crit reached its maximum value. Top: stellar masses are 0.15 M_⊙. Middle: stellar masses are 0.3 M_⊙. Bottom: stellar masses are 0.45 M_⊙. The approximate runtime was 6 min in total. github.com: cbp_dynamic_stability/HZ_Evolution/