ar X iv : a st ro - p h / 05 09 76 7 v 1 2 6 Se p 20 05 Planets in triple star systems — the case of HD 188753

We consider the formation of the recently discovered “hot Jupiter” planet orbiting the primary component of the triple star system HD188753. Although the current outer orbit of the triple is too tight for a Jupiter-like planet to have formed and migrated to its current location, the binary may have been much wider in the past. We assume here that the planetary system formed in an open star cluster, the dynamical evolution of which subsequently led to changes in the system’s orbital parameters and binary configuration. We calculate cross sections for various scenarios that could have led to the multiple system currently observed, and conclude that component A of HD188753 with its planet were most likely formed in isolation to be swapped in a triple star system by a dynamical encounter in an open star cluster. We estimate that within 500 pc of the Sun there are about 1200 planetary systems which, like Hd188753, have orbital parameters unfavorable for forming planets but still having a planet, making it quite possible that the HD188753 system was indeed formed by a dynamical encounter in an open star cluster. Subject headings: methods: N-body simulations – planets and satellites: individual HD188753 – planetary systems: formation – Astronomical Institute “Anton Pannekoek,” University of Amsterdam, Kruislaan 403, 1098 SH Amsterdam, NL Department of Computer Science, University of Amsterdam, Kruislaan 403, 1098 SH Amsterdam, NL Department of Physics,Drexel University, Philadelphia, PA 19104, USA [email protected]