The depletion of the red supergiant envelope radiative zone during common envelope evolution

Abstract We conduct one-dimensional stellar evolution simulations of red supergiant (RSG) stars that mimic common envelope (CEE) and find the inner boundary convective zone moves into initial radiative zone. The convection practically disappears only when RSG radius decreases by about an order magnitude or more. implication is one cannot split CEE stage during which companion spirals-in inside removes it, a second slower phase orbits stable mass transfer takes place. At best, this might take place orbital separation several solar radii. However, time other processes become important. conclude as yet, commonly used alpha-formalism based on energy considerations best phenomenological formalism.