Planetesimal accretion in Alpha Centauri

We investigate planet formation around Alpha Cen A and B, focusing on the crucial planetesimals-to-embryos phase. We use an N-body code estimating the impact velocity distribution within a population of test planetesimalshaving variable size distributions. We find that the coupling between binary secular perturbations and gas friction strongly affects the encounter velocity evolution, increasing impact velocities for all impacts between objects of different sizes. For all tested planetesimalsize distributions and gas disc profiles, we find that this excited dynamical environment is hostile to accretion in the region beyond 0.75 AU from the individual stars. However, the presence of planets in these regions cannot be fully ruled out, since additional effects, like hypothetical outward planet migrations or different binary orbital parameters in the past, might have played a role. A robust result is however that we confirm that the phase of mutual accretion between km-sized planetesimalsis much more sensitive to binary perturbations than the following phase of accretion of large embryos.