Configurations of bounded and free-floating planets in very young open clusters

Abstract

Open clusters (OCs) are usually young and suitable for studying the formation and evolution of planetary systems. So far, only four planets have been found with radial velocity measurements in OCs. Meanwhile, a lot of free-floating planets (FFPs) have been detected. We utilize N-body simulations to investigate the evolution and final configurations of multi-planetary systems in very young open clusters with an age <10 Myr. After an evolution of 10 Myr, 61%-72% of the planets remain bounded and more than 55% of the planetary systems will maintain their initial orbital configurations. For systems with one planet ejected, more than 25% of them have the surviving planets in misaligned orbits. In the clusters, the fraction of planetary systems with misalignment is >6%, and only 1% have planets in retrograde orbits. We also obtain a positive correlation between the survival planet number and the distance from the cluster center r: planetary systems with a larger r tend to be more stable. Moreover, stars with a mass >2.5 M⊙ are likely unstable and lose their planets. These results are roughly consistent with current observations. Planetary systems in binaries are less stable and we achieve a rough criterion: most of the binary systems with ab(1-e 2b) >100 AU can retain all the initial planets. Finally, 80% of the FFPs are ejected out of the clusters, while the rest (∼20%) still stay in host clusters and most of them are concentrated in the center (<2 pc). © 2013. The American Astronomical Society. All rights reserved.