Common envelopes in massive stars II: The distinct roles of hydrogen and helium recombination

The role of recombination during a common-envelope event has been long debated. Many studies have argued that much hydrogen energy, which is radiated in relatively cool and optically-thin layers, might not thermalise the envelope. On other hand, helium contains 30% total occurs deeper stellar We investigate distinct roles played by interaction experienced 12 solar mass red supergiant donor. perform adiabatic, 3D hydrodynamical simulations (i) include hydrogen, helium, molecular recombination, (ii) (iii) only (iv) do energy. By comparing these simulations, we find addition energy alone ejects more envelope mass, leads to 16% larger post-plunge-in separation. Under adiabatic assumption, adding increases amount ejected further 40%, possibly unbinding entire envelope, but does affect post-plunge Most ejecta becomes unbound at high (>70%) degrees ionisation, where likely expand instead being away.