Abstract
Aims. Hot Jupiters are thought to belong to single-planet systems. Somewhat surprisingly, some hot Jupiters have been reported to exhibit transit timing variations (TTVs). The aim of this paper is to identify the origin of these observations, identify possible periodic biases leading to false TTV detections, and refine the sample to a few candidates with likely dynamical TTVs. Methods. We present TTV frequencies and amplitudes of hot Jupiters in Kepler Q0--6 data with Fourier analysis and a frequency-dependent bootstrap calculation to assess the false alarm probability levels of the detections. Results. We identified 36 systems with TTV above four standard deviation confidence, about half of them exhibiting multiple TTV frequencies. Fifteen of these objects (HAT-P-7b, KOI-13, 127, 183, 188, 190, 196, 225, 254, 428, 607, 609, 684, 774, 1176) probably show TTVs due to a systematic observational effect: long cadence data sampling is regularly shifted transit-by-transit, interacting with the transit light curves, introducing a periodic bias, and leading to a stroboscopic period. For other systems, the activity and rotation of the host star can modulate light curves and explain the observed TTVs. By excluding the systems that were inadequately sampled, showed TTV periods related to the stellar rotation, or turned out to be false positives or suspects, we ended up with seven systems. Three of them (KOI-186, 897, 977) show the weakest stellar rotation features, and these are our best candidates for dynamically induced TTV variations. Conclusions. Those systems with periodic TTVs that we cannot explain with systematics from observation, stellar rotation, activity, or inadequate sampling may be multiple systems or even exomoon hosts.
Highlights
Transit timing variation (TTV) is a major diagnostics of various system parameters of extrasolar planets (Holman & Murray 2005; Agol et al 2005)
Fifteen detections showed stroboscopic periods only (Sect. 3.1), and two additional systems were excluded from the beginning, because the TTV period was found to agree with the rotation period of the host star: (KOI-883) and Kepler-17b
We found that the TTV periods of three more objects are related to the stellar rotation period (Sect. 3.2) based on their Kepler light curves (KOI-412, 822, 895)
Summary
Transit timing variation (TTV) is a major diagnostics of various system parameters of extrasolar planets (Holman & Murray 2005; Agol et al 2005). According to our current view, hot Jupiters occur as single planets, since they have been not detected in multiplanet systems. This picture suggests that hot Jupiters occupy unperturbed orbits, their orbital motion is Keplerian, and they exhibit strictly periodic transit times. In contrast to this picture, current literature reports a considerable number of hot Jupiters with TTV, which are often periodic (Steffen et al 2012a; Ford et al 2012b). We briefly introduce the most exciting systems and discuss the possible sources of TTVs for these planets
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