Donor radius as a function of mass in thermal equilibrium (blue). The red lines show the Roche radius as a function of donor mass during the binary calculation that includes a 10 M_⊙ accretor and no stellar wind of the donor. The yellow lines show the Roche radius after the binary calculation has stopped and CE is initiated. The orbital separation and hence the Roche radius was inferred using the energy budget description of CE. The green area marks the position of the H/He transition layer.