Identifying Transiting Circumbinary Planets

Abstract

Abstract. Transiting planets manifest themselves by a periodic dimming of their host star by a fixed amount. On the other hand, light curves of transiting circumbinary (CB) planets are expected to be neither periodic nor to have a single depth while in transit, making the BoxLeast-Squares (BLS) transit detection method almost ineffective. Therefore, a modified version for the identification of CB planets was developed -CB-BLS. We show that using CB-BLS it is possible to find CB planets in the residuals of light curves of eclipsing binaries (EBs) that have noise levels of 1% or more. Using CB-BLS will allow us to use the massive ground-and spacebased photometric surveys to look for these objects. Detecting transiting CB planets is expected to have a wide range of implications. For instance, the frequency of CB planets depends on the planetary formation mechanism -and planets in close pairs of stars provide a most restrictive constraint on planet formation models. Furthermore, understanding very high precision light curves is limited by stellar parameters -and since for EBs the stellar parameters are much better determined, the resultant planetary structure models will have significantly smaller error bars, maybe even small enough to challenge theory. The ChallengeLight curves (LCs) of transiting planets around single stars have precise depths, durations and epochs -and changes in any of these tell us something about the system. Light curves of transiting CB planets are expected to have very different photometric and temporal characteristics (Fig. 1), where none of these properties hold (Schneider & Chevreton 1990, Schneider 1994. In general, photometric signal = blocked flux / total flux, but for CB planets neither is constant: the total flux changes all the time because of ellipsoidal variation and binary eclipses. The blocked flux varies according to the surface brightness of the binary component being transited. The temporal characteristics arise from the fact that the transits are not periodic, and that their duration is highly variable -depending more on the transversal velocity of the binary components than on the planetary motion (the binary components can move either parallel or anti-parallel to the planet's motion, enabling long and short transits, respectively). Deeg et al. 1998). The leftmost panel shows the normal case, with two short and separated transits. The second panel shows a planetary transit near a binary mutual eclipse -producing a long transit. The two rightmost panels show transits of a planet with a long period: such planets have a transversal velocity that is slower than the binary components, and multiple transits with complicated shapes are more likely to occur.

Circumbinary Planets and the SOLARIS Project

“…Likely, also the dynamical interaction between protoplanets and then planets in a multi-planet system should be affected by the central body binarity and presumably result in a different distribution of the orbital elements of planets. Finally, if one assumes that planetary orbits are coplanar with the orbit of an eclipsing binary, then there is an enhanced probability of detecting a circumbinary transiting planet (Konacki 2009a, Ofir 2008, Ofir 2009, Schneider & Chevreton 1990, Schneider 1994.…”

The Radial Velocity Tatooine Search for Circumbinary Planets: Planet Detection Limits for a Sample of Double-Lined Binary Stars—initial Results From Keck I/Hires, Shane/Cat/Hamspec, and TNG/Sarg Observations

“…Likely, also the dynamical interaction between protoplanets and the planets in a multi-planet system should be affected by the central body binarity and presumably result in a different distribution of the orbital elements of planets. Finally, if one assumes that planetary orbits are coplanar with the orbit of an eclipsing binary, then there is an enhanced probability of detecting a circumbinary transiting planet (Konacki 2009;Ofir 2009Ofir , 2008Schneider 1994;Schneider & Chevreton 1990).…”