Detecting binary star planetary and brown dwarf companions from analysis of eclipse timing variations

Detecting binary star planetary and brown dwarf companions from analysis of eclipse timing variations

Binary stars have long been known to show mutual and precisely periodic eclipses, if their orbit is favourably inclined to our line of sight. However, more recently space telescope missions such as Kepler have provided long-term precision light-curves for thousands of stars, enabling analyses of binary star eclipse timing variations to search for perturbing low-mass sub-stellar companions, namely brown dwarfs and planets. This thesis thus comprises three interrelated studies, as follows.

(1) The extent to which eclipse time variations can detect binary star low-mass bodies is simulated for Kepler Eclipsing Binary Star Catalog stars using empirical data from the catalog as a starting point. The analysis finds that even planetary mass companions are readily detectable with eclipse time variations, although successful detection is strongly dependent on the orbital period of the host eclipsing binary star, and the orbital period and eccentricity of the third body. The detectable range of companion body masses and orbital periods also can be reliably estimated simply, using just two equations.

(2) In a study of orbital dynamics, for those binary stars found to produce complex eclipse timing variations, their evolving system orbital configuration is inferred, and their long-term dynamical stability is simulated. The analysis finds that even complex eclipse time variations are explainable by low-mass, even planetary, companions in stable orbits, and where highly eccentric third bodies around eccentric binary stars can explain a complex 'flip-flop' feature seen in some observed-calculated diagrams. For some proposed new low-mass companions, the simulated orbits are expected to be stable over long dynamical timescales, with the companions remaining detectable.

(3) In terms of new planetary detections, in a study of KIC 5095269, a planietary mass companion has been found in a highly inclined orbit relative to the orbit of the host stars. The eclipse time variation analysis for this system indicates a 7.70 Jupiter mass planet in a 237.7 day orbit, stable for at least ten million years.

In conclusion, this thesis has established the feasibility of eclipsing timing variations as a way to survey binary stars for brown dwarf and planetary companions. In the future, space telescope surveys such as those being done by the Transiting Exoplanet Survey Satellite (TESS) will accrue additional useful eclipsing binary star light curves, and enable more extensive searches for binary star low-mass companions.

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