* Astronomy

Title: A deeper view of the CoRoT-9 planetary system. A small non-zero eccentricity for CoRoT-9b likely generated by planet-planet scattering
Author: A. S. Bonomo, G. Hébrard, S. N. Raymond, F. Bouchy, A. Lecavelier des Etangs, P. Bordé, S. Aigrain, J.-M. Almenara, R. Alonso, J. Cabrera, Sz. Csizmadia, C. Damiani, H. J. Deeg, M. Deleuil, R. F. Díaz, A. Erikson, M. Fridlund, D. Gandolfi, E. Guenther, T. Guillot, A. Hatzes, A. Izidoro, C. Lovis, C. Moutou, M. Ollivier, M. Pätzold, H. Rauer, D. Rouan, A. Santerne, J. Schneider

CoRoT-9b is one of the rare long-period (P=95.3 days) transiting giant planets with a measured mass known to date. We present a new analysis of the CoRoT-9 system based on five years of radial-velocity (RV) monitoring with HARPS and three new space-based transits observed with CoRoT and Spitzer. Combining our new data with already-published measurements we redetermine the CoRoT-9 system parameters and find good agreement with the published values. We uncover a higher significance for CoRoT-9b's small but non-zero eccentricity (e=0.133^{+0.042}_{-0.037}) and find no evidence for additional planets in the system. We use simulations of planet-planet scattering to show that CoRoT-9b's eccentricity may have been generated by an instability in which a ~50 earth mass planet was ejected from the system. This scattering would not have produced a spin-orbit misalignment, so we predict that CoRoT-9b's orbit should lie within a few degrees of the initial plane of the protoplanetary disk. As a consequence, any significant stellar obliquity would indicate that the disk was primordially tilted.

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