ON THE BINDING ENERGY PARAMETER λ OF COMMON ENVELOPE EVOLUTION

The binding energy parameter λ plays an important role in common envelope evolution. Previous works have already pointed out that λ varies throughout the stellar evolution, though it has been adopted as a constant in most of the population synthesis calculations. We have systematically calculated the binding energy parameter λ for both Population I and Population II stars of masses 1–20 M ☉ , taking into account the contribution from the internal energy of stellar matter. We present fitting formulae for λ that can be incorporated into future population synthesis investigations. We also briefly discuss the possible applications of the results in binary evolutions.