Volume 618, October 2018
|Number of page(s)||22|
|Section||Planets and planetary systems|
|Published online||11 October 2018|
Kepler Object of Interest Network★
II. Photodynamical modelling of Kepler-9 over 8 years of transit observations
Institut für Astrophysik,
37077 Göttingen, Germany
2 Stellar Astrophysics Centre, Aarhus University, Ny Munkegade 120, 8000 Aarhus, Denmark
3 Rosseland Centre for Solar Physics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
4 Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
5 Astronomy Department, University of Washington, Seattle, WA 98195, USA
6 Institut d’Astrophysique de Paris, 98 bis Boulevard Arago, 75014 Paris, France
7 Virtual Planetary Laboratory, University of Washington, USA
8 Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
9 Instituto de Astrofísica de Canarias, C. Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
10 Universidad de La Laguna, Departamento de Astrofísica, 38206 La Laguna, Tenerife, Spain
11 Aix-Marseille Université, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France
12 Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, 76100, Israel
13 School of Geosciences, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, 6997801, Israel
14 Institut de Cincies de l’Espai (IEEC-CSIC), C. Can Magrans s/n, Campus UAB, 08193 Bellaterra, Spain
15 Institut Estudis Espacials de Catalunya (IEEC), C. Gran Capit4, Edif. Nexus, 08034 Barcelona, Spain
16 Hamburg Observatory, Hamburg University, Gojenbergsweg 112, 21029 Hamburg, Germany
17 Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
18 Instituto de Astronomía, UNAM, Campus Ensenada, Carretera Tijuana-Ensenada km 103, 22860 Ensenada, México
Accepted: 28 June 2018
Context. The Kepler Object of Interest Network (KOINet) is a multi-site network of telescopes around the globe organised to follow up transiting planet-candidate Kepler objects of interest (KOIs) with large transit timing variations (TTVs). Its main goal is to complete their TTV curves, as the Kepler telescope no longer observes the original Kepler field.
Aims. Combining Kepler and new ground-based transit data we improve the modelling of these systems. To this end, we have developed a photodynamical model, and we demonstrate its performance using the Kepler-9 system as an example.
Methods. Our comprehensive analysis combines the numerical integration of the system’s dynamics over the time span of the observations along with the transit light curve model. This provides a coherent description of all observations simultaneously. This model is coupled with a Markov chain Monte Carlo algorithm, allowing for the exploration of the model parameter space.
Results. Applied to the Kepler-9 long cadence data, short cadence data, and 13 new transit observations collected by KOINet between the years 2014 and 2017, our modelling provides well constrained predictions for the next transits and the system’s parameters. We have determined the densities of the planets Kepler-9b and 9c to the very precise values of ρb = 0.439 ± 0.023 g cm−3 and ρc = 0.322 ± 0.017 g cm−3. Our analysis reveals that Kepler-9c will stop transiting in about 30 yr due to strong dynamical interactions between Kepler-9b and 9c, near 2:1 resonance, leading to a periodic change in inclination.
Conclusions. Over the next 30 years, the inclination of Kepler-9c (-9b) will decrease (increase) slowly. This should be measurable by a substantial decrease (increase) in the transit duration, in as soon as a few years’ time. Observations that contradict this prediction might indicate the presence of additional objects in this system. If this prediction turns out to be accurate, this behaviour opens up a unique chance to scan the different latitudes of a star: high latitudes with planet c and low latitudes with planet b.
Key words: planetary systems / planets and satellites: dynamical evolution and stability / methods: data analysis / techniques: photometric / stars: individual: Kepler-9 / stars: fundamental parameters
Ground-based photometry is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/618/A41
© ESO 2018
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