Planets in binary systems: is the present configuration indicative of the formation process?

Aims. The present dynamical configuration of planets in binary sta r systems may not reflect their formation process since the bi nary orbit may have changed in the past after the planet formation process was completed. An observed binary system may have been part of a former hierarchical triple that became unstable after t he planets completed their growth around the primary star. Alternatively, in a dense stellar environment even a single stellar encounter between the star pair and a singleton may singificantly alt er the binary orbit. In both cases the planets we observe at present would have formed when the dynamical environment was different from the presently observed one. Methods. We have numerically integrated the trajectories of the star s (binary plus singleton) and of test planets to investigate the abovementioned mechanisms. The orbits of the planets have been computed to test the survival of a planetary system around the primary during the chaotic phase of the stars. Results. Our simulations show that the circumstellar environment during planetary formation around the primary was gravitationally less perturbed when the binary was part of a hierarchical tri ple because the binary was necessarely wider and, possibly, less eccentric. This circumstance has consequences for the planetary system in terms of orbital spacing, eccentricity, and mass of the i ndividual planets. Even in the case of a single stellar encounter the pr esent appearance of a planetary system in a binary may signifi cantly differ from what it had while planet formation was ongoing. However, while in the case of instability of a triple the trend is alwa ys towards a tighter and more eccentric binary system, when a single stellar encounter affects the system the orbit of the binary can become wider and be circularized. Conclusions. Modelling the formation of a planetary system around a binary is a potentially complex task and an effort has to be made to look into its present dynamics for traces of a possible chaotic past.