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Session 44 - Double Stars.
Display session, Thursday, January 08
Exhibit Hall,
The evolution of binary systems consisting of an asymptotic giant branch (AGB) star of mass equal to 3 M_ødot or 5 M_ødot, and a main sequence star of mass equal to 0.4 M_ødot or 0.6 M_ødot with orbital periods greater than 200 days has been followed from the onset through the late stages of the common envelope phase. Using a nested grid technique, the three-dimensional hydrodynamical simulations indicate that a significant fraction of the envelope gas is unbound (\sim 20 - 30%) by the ends of the simulations, and that the efficiency of the mass ejection process had a range of 0.4 < \alpha_CE < 0.6 (with a high value found for a simulation involving a more evolved 5 M_ødot giant). While the original volume of the giant is virtually evacuated in the late stages, most of the envelope gas remains marginally bound on the grid. At the ends of our simulations, when the orbital decay timescale exceeds about 5 years, the giant core and companion orbit one another with a period less than about 1 day. For a binary of 5 M_ødot and 0.4 M_ødot, the common envelope may not be completely ejected. The results are not found to be sensitive to the degree to which the initial binary system departs from the synchronous state.
