Abstract:
The origin of chemically peculiar stars and non-zero eccentricity in evolved close binaries have been long-standing problems in binary stellar evolution. Answers to these questions may trace back to an intense mass transfer during an AGB binary phase. In this talk, I will discuss two mass transfer modes in the AGB binaries and the transition between them. One mass transfer mode is the well known Bondi-Hoyle-Lyttleton (BHL) accretion and the other is called the Wind-Roche-lobe overflow (WRLOF). We use AstroBEAR to solve radiationhydrodynamic equations in 3D and calculate mass transfer rates in asymptotic-giant-branch (AGB) binaries with different binary separations. Accretion disks may form around the secondaries. Depending on the binary separation, a circumbinary disk or a spiral structure may appear in the simulation. The resulting mass transfer efficiency in our models is up to a factor of 8 times higher than what the standard BHL accretion scenario predicts, and the outflow gains up to 91% of its initial angular momentum when it reaches 1.3 binary separations. Consequently, some AGB binaries may undergo orbit shrinkage, and some will expand. The high mass transfer efficiency is closely related to the presence of the circumbinary disks.
