Discovering Multiple Exoplanet Systems Hidden in Kepler Data

Dr. Daniel Fabrycky visited NAOC on January 14, 2015 and gave a presentation entitled "Architecture and Timing of Planetary Systems". Dr. Fabrycky recently graduated with his Ph.D. from Princeton University and is now an Assistant Professor at the University of Chicago. His research area has concentrated on the rich field of exoplanets. He started the talk by giving an overview of various methods that can be used for exoplanet detection, including changes in radial velocity and microlensing. He showed how results from the Kepler mission have dramatically increased the number of exoplanet candidates and confirmed cases. Moreover, because Kepler relies on transit observations to initiate follow-up studies, more properties of planets are derivable from data collected by the Kepler mission than from other methods. For example, from the results of analyzing Kepler data, he showed that adding only a small amount of hydrogen or helium to the material composing a planet can dramatically increase its size.

Dr. Fabrycky then turned to his own work which concentrates on processing Kepler data in novel ways to detect multiple planetary systems. His work involves using known transit times of planets to uncover planets that have not been directly observed through perturbations. Theorists previously predicted that planets should perturb each other in multiple planetary systems and that the effects of these perturbations should show up as accelerations or decelerations in the observed orbital speeds of planets. Because the Kepler mission has a high duty cycle, making almost continuous observations of a large number of stars, small changes in the observed orbital speed of some planets are detectable. Dr. Fabrycky showed that through an advanced analysis of Kepler data, he has demonstrated that some systems are composed of six or seven planets, even though only two or three of these planets are directly observable by Kepler. He continued his talk by explaining how his advanced method of data analysis can be used to find how far the orbits of planetary systems depart from being a flat plane. However, he mentioned that, according to the data analyzed so far, most planetary systems are, like our Solar System, very close to being flat planes.

Dr. Fabrycky concluded his talk by commenting on how much data archived by the Kepler mission still need to be analyzed. He also mentioned that it is possible other kinds of interactions can cause similar variations in orbital speed, for example, interactions between a planet and its moon. However, he warned that the best confirmation of a moon orbiting an exoplanet should be made photometrically instead of through this method, since the photometric results would be irrefutable.

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