A deeper view of the CoRoT-9 planetary system

A small non-zero eccentricity for CoRoT-9b likely generated by planet-planet scattering

¹ INAF–Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
e-mail: bonomo@oato.inaf.it
² Institut d’Astrophysique de Paris, CNRS, UMR 7095 & Sorbonne Universités, UPMC Paris 6, 98 bis bd Arago, 75014 Paris, France
³ Observatoire de Haute Provence, Université Aix-Marseille & CNRS, 04870 St. Michel l’ Observatoire, France
⁴ Laboratoire d’Astrophysique de Bordeaux, Université de Bordeaux, CNRS, B18N, Allée Geoffroy Saint-Hilaire, 33615 Pessac, France
⁵ Observatoire de l’Université de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland
⁶ Department of Physics, Denys Wilkinson Building Keble Road, Oxford, OX1 3RH, UK
⁷ Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife, Spain
⁸ Universidad de La Laguna, Dept. de Astrofísica, 38200 La Laguna, Tenerife, Spain
⁹ Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
¹⁰ Institut d’Astrophysique Spatiale, UMR 8617, CNRS – Université de Paris-Sud – Université Paris-Saclay – Bât. 121, 91405 Orsay, France
¹¹ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
¹² Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Buenos Aires, Argentina
¹³ CONICET – Universidad de Buenos Aires, Instituto de Astronomía y Física del Espacio (IAFE), Buenos Aires, Argentina
¹⁴ Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA, Leiden, The Netherlands
¹⁵ Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Swden
¹⁶ Dipartimento di Fisica, Università di Torino, via P. Giuria 1, 10125 Torino, Italy
¹⁷ Thüringer Landessternwarte, Sternwarte 5, Tautenburg 5, 07778 Tautenburg, Germany
¹⁸ Observatoire de la Côte d’Azur, Laboratoire Cassiopée, BP 4229, 06304 Nice Cedex 4, France
¹⁹ UNESP, Univ. Estadual Paulista – Grupo de Dinâmica Orbital & Planetologia, Guaratinguetá, CEP 12. 516-410, São Paulo, Brazil
²⁰ CNRS, CFHT Corporation, 65-1238 Mamalahoa Hwy, Kamuela, HI 96743, USA
²¹ LESIA, Obs. de Paris, Place J. Janssen, 92195 Meudon Cedex, France
²² Rheinisches Institut für Umweltforschung an der Universität zu Köln, Aachener Strasse 209, 50931 Köln, Germany
²³ Center for Astronomy and Astrophysics, TU Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
²⁴ LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France

Received: 15 February 2017
Accepted: 17 March 2017

Abstract

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 the small but non-zero eccentricity of CoRoT-9b (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 the eccentricity of CoRoT-9b may have been generated by an instability in which a ~ 50 M_⊕ planet was ejected from the system. This scattering would not have produced a spin-orbit misalignment, so we predict that the CoRoT-9b 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.