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E. L. Sandquist, R. E. Taam (Northwestern U.), A. Burkert (MPIA - Heidelberg)
We present the results of three-dimensional hydrodynamics simulations of the common envelope phase in the evolution of a binary system containing a first-ascent red giant primary star and a low mass secondary. We have conducted runs as a function of evolutionary state (helium core mass) for the 2 Msun primary. For the primary with the smallest core mass (0.25 Msun), the companion star (modelled as a point mass of 0.2 Msun) spirals completely through the envelope of the giant star without showing signs of finding a stable orbit. By the end of the simulation, less than 10% of the giant's gas envelope becomes gravitationally unbound from the system, meaning that the bound gas can help accelerate the orbital decay of the secondary. For a more evolved giant, the spatially extended low-mass region that develops around its core facilitates the establishment of a stable short-period binary. We will use additional simulations to estimate the minimum core mass for which a stable binary can be formed. The implications of these results for pre-cataclysmic variables and low-mass helium double degenerate systems will be discussed.
The author(s) of this abstract have provided an email address for comments about the abstract: erics@apollo.astro.nwu.edu