Student Posters Repository

We study the common-envelope evolution of a 1.2 Msol AGB star. By including recombination energy, we succeed in ejecting and gravitationally unbinding a substantial part of the envelope. Hydrodynamical simulations of giant stars are difficult due to the wide range in spatial scales and in dynamical timescales. Especially the weakly bound envelope of the AGB star has caused problems previously. After mapping a one-dimensional stellar profile from mesa onto the grid and relaxing the giant’s atmosphere to obtain a stable model, we perform a three-dimensional binary simulation of the hydrodynamics with an adaptive mesh code, where dynamical instabilities can be observed. Considering different companion star masses, we discuss the ejection of the envelope. The dynamics are governed by dynamical friction and shocks. Taking into account recombination energy, the unbound mass fraction can be increased significantly, ejecting the envelope completely. The common-envelope phase thus can be considered as a mechanism leading to close binary systems, driven by recombination.