Dynamics of co-orbital planets in Double stars

Up to now, 460 out of the 500 extrasolar planets discovered are orbiting around single stars. Nevertheless, in the solar neighbourhood 70 percent of the main sequence stars are members of double stars and multiple systems. Therefore, we expect that many more planets may exist in binary systems. There are several detection methods for extrasolar planets, the two most common ones are the radial velocity method and the transit method. Currently, we know more than 100 extrasolar planets detected by the transit method. Some of them were found with the space missions, CoRoT (launched 2006) and Kepler (launched 2009). In the quest for new exoplanets close, eclipsing binaries are promising candidates because many lie in the CoRoT and Kepler discovery space. In general we distinguish three dynamical types of motion for extrasolar planets in binary star systems: 1. S-Type: A planet orbits one of the two stars. 2. P-Type: A planet stays in an orbit around both stars. 3. T-Type: A planet may orbit close to one of the equilibrium points L4 and L5 . This project is dedicated to the dynamics and the theory of observations of planets in S- and T-Type configurations in binary star systems. We will do these investigations with the aid of extensive numerical integrations. With the help of stability studies, we want to understand the role of mean motion resonances and secondary resonances in transit timing of eclipsing binaries. In addition, we want to identify regions in the orbital parameter space where extrasolar planets can have stable orbits. In a further step, we will concentrate on the discovery of planets in S- and P-Type motion. This will be realized via investigations of eclipse timing variations (ETV). With the ETVs we will show whether it is possible to detect planet induced perturbations in the transit signal of the secondary star. The results of this project can serve as a guideline for actual and future observations - especially satellite missions - and will improve our understanding of the architecture of extrasolar planets in binary systems.

Many exoplanets were discovered orbiting around single stars. Nevertheless in the solar neighbourhood around 70 percent of the main sequence stars are members of binary and multiple star systems. Therefore, many more planets around double stars were expected. This discrepancy was the motivation for the project to investigate the orbital stability of exoplanets in co-orbital motion in double star systems (binaries). Co-orbital means that the planet is close to or in the same orbit as the secondary star. Up to now no planet in co-orbital motion was found. But in the solar system we know more than 6000 co-orbital asteroids (close to Earth, Mars, Jupiter, Uranus and Neptune). This project had the goal to improve the probability to detect Trojan planets by the help of stability studies, the investigation of eclipse timing variations (ETVs) and by analysing possible candidate systems. In the stability study we investigated the dynamical behaviour of possible planets in Trojan-type and Satellite-type motion in binary star systems using numerical integrations. Therefore, we did N-body simulations in the three-dimensional parameter space. In the second part we concentrated on the observability of such systems. Thus, we studied the possibility for the detection of such planets in binaries with the eclipse timing method. If a binary star system is aligned such that the stars pass in front of each other in their orbits, the system is called an eclipsing binary star system. Is the eclipsing binary gravitational influenced by a planet then the eclipses of the binaries show a shift in the occultation time, like the planet which was found in the system Kepler-451. We have shown that even terrestrial-like planets are detectable in binary-star systems by using ETVs. As basis for our statistics we started in 2013 to compile a catalogue for exoplanets in binary and multiple star systems (http://www.univie.ac.at/adg/schwarz/multiple.html) because at that time there was no list of exoplanets in binary star systems available. For the choice of our parameter-space of our calculations we analyzed statistically our catalogue. In addition to these statistics of the catalogue we enlarged them by the investigation of well-detached binary star systems from several catalogues (stars without planets) and discussed the possibility of further candidates. In collaboration with the space research institute in Graz we investigated the WASP-12 and HD 189733 systems where the transits of a hot Jupiter (close to the star) leave a signature in the observations, similar to a plasma torus. From a dynamical point of view these phenomena maybe explained as Moon-sized Trojans. The obtained knowledge will pave the way for future observations, owing to the fact that the knowledge of precise planetary motion is a key factor to understand the evolution and structure of planetary systems and possibly their evolution to Earth-like habitable planets.