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Circumbinary planets - why they are so likely to transit

Martin, David V. ; Triaud, Amaury H. M. J.

In: Monthly Notices of the Royal Astronomical Society, 2015, vol. 449, no. 1, p. 781-793

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    Title
    • Circumbinary planets - why they are so likely to transit
    Author
    • Martin, David V.. Observatoire de Genève, Université de Genève, 51 chemin des Maillettes, Sauverny CH-1290, Switzerland
    • Triaud, Amaury H. M. J.. Department of Physics, and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
    Document Type
    • Postprint
    Language
    • English
    Published in
    • Monthly Notices of the Royal Astronomical Society, 2015, vol. 449, no. 1, p. 781-793. Oxford University Press
    Other Version
    OAI-PMH Identifier
    • oai:doc.rero.ch:297260
    Summary
    Transits on single stars are rare. The probability rarely exceeds a few per cent. Furthermore, this probability rapidly approaches zero at increasing orbital period. Therefore, transit surveys have been predominantly limited to the inner parts of exoplanetary systems. Here, we demonstrate how circumbinary planets allow us to beat these unfavourable odds. By incorporating the geometry and the three-body dynamics of circumbinary systems, we analytically derive the probability of transitability, a configuration where the binary and planet orbits overlap on the sky. We later show that this is equivalent to the transit probability, but at an unspecified point in time. This probability, at its minimum, is always higher than for single star cases. In addition, it is an increasing function with mutual inclination. By applying our analytical development to eclipsing binaries, we deduce that transits are highly probable, and in some case guaranteed. For example, a circumbinary planet revolving at 1 au around a 0.3 au eclipsing binary is certain to eventually transit - a 100 per cent probability - if its mutual inclination is greater than 0 $_{.}^{\circ}$6. We show that the transit probability is generally only a weak function of the planet's orbital period; circumbinary planets may be used as practical tools for probing the outer regions of exoplanetary systems to search for and detect warm to cold transiting planets