Debris disc candidates in systems with transiting planets

ABSTRACT

Debris discs are known to exist around many planet-host stars, but no debris dust has been found so far in systems with transiting planets. Using publicly available catalogues, we searched for infrared excesses in such systems. In the recently published Wide-field Infrared Survey Explorer catalogue, we found 52 stars with transiting planets. Two systems with one transiting ‘hot Jupiter’ each, TrES-2 and XO-5, exhibit small excesses both at 12 and at 22 μ m at a ≳3σ level. Provided that one or both of these detections are real, the frequency of warm excesses in systems with transiting planets of 2–4 per cent is comparable to that around solar-type stars probed at similar wavelengths with Spitzer’s MIPS and IRS instruments. Modelling suggests that the observed excesses would stem from dust rings with radii of several  au. The inferred amount of dust is close to the maximum expected theoretically from a collisional cascade in asteroid belt analogues. If confirmed, the presence of debris discs in systems with transiting planets may put important constraints on the scenario of formation and migration of hot Jupiters.