The disappearing transits of Kepler-9c

Combining 9 years of space-based observations and ground-based follow-ups, we carried out a photodynamical analysis of the Kepler-9 system revealing disappearing transits of Kepler-9c in about 30 years. This results from strong dynamical interactions between Kepler-9b and c in near 2:1 resonance, that leads to a periodical change in inclination. Over the next 30 years the inclination of Kepler-9c will decrease slowly, that should be measurable by a substantial decrease in the transit duration in a few years already. This behaviour gives us a unique chance to scan the limb darkening of a star.

Our comprehensive analysis combines the numerical integration of the system’s dynamics over the time span of observations with the transit light curve model to provide a coherent description of all observations simultaneously. We developed it as part of the KOINet, a multi-site network of telescopes around the globe organized to follow-up KOIs with large TTVs, to ensure an adequate modelling of our objects. Our model is coupled with a Markov chain Monte Carlo algorithm, that helps explore the parameter space. Applied to the Kepler-9 long cadence data, short cadence data and 13 new transit observations from the years 2014 - 2017 obtained by the KOINet, our modelling reveals these pleasing results and gives strongly directing predictions.

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