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In low-mass binary systems, mass transfer is likely to occur via a slow anddense stellar wind when one of the stars is in the AGB phase. Observations showthat many binaries that have undergone AGB mass transfer have orbital periodsof 1-10 yr, at odds with the predictions of binary population synthesis models.We investigate the mass-accretion efficiency and angular-momentum loss via windmass transfer in AGB binary systems. We use these quantities to predict theevolution of the orbit. We perform 3D hydrodynamical simulations of the stellarwind lost by an AGB star using the AMUSE framework. We approximate the thermalevolution of the gas by imposing a simple effective cooling balance and we varythe orbital separation and the velocity of the stellar wind. We find that forwind velocities $v_{\infty}$ larger than the relative orbital velocity of thesystem $v_\mathrm{orb}$ the flow is described by the Bondi-Hoyle-Lyttletonapproximation and the angular-momentum loss is modest, leading to an expansionof the orbit. For low wind velocities an accretion disk is formed around thecompanion and the accretion efficiency as well as the angular-momentum loss areenhanced, implying that the orbit will shrink. We find that the transfer ofangular momentum from the orbit to the outflowing gas occurs within a feworbital separations from the center of mass of the binary. Our results suggestthat the orbital evolution of AGB binaries can be predicted as a function ofthe ratio $v_{\infty}/v_\mathrm{orb}$. Our results can provide insight into thepuzzling orbital periods of post-AGB binaries and suggest that the number ofstars entering into the common-envelope phase will increase. The latter canhave significant implications for the expected formation rates of the endproducts of low-mass binary evolution, such as cataclysmic binaries, type Iasupernova and double white-dwarf mergers. [ABRIDGED]

Gone with the wind: the impact of wind mass transfer on the orbital evolution of AGB binary systems