Boundaries for unstable MT (red) and the formation of GW sources (blue) for a 32 M_⊙ donor orbiting a CO of mass m_a, i. The area below the gray line excludes systems for which the final orbital separation implies R_d, f <  R_RL, f. Results are shown for full isotropic re-emission (solid) and assuming all matter is ejected from L₂ (dashed line). Different stages of evolution are illustrated by contours of constant Roche lobe radius (dotted gray line). Empty circles mark the formation of a convective envelope containing 10% of the donor’s mass.