Measurements of Transit Timing Variations for WASP-5b

Abstract We observed 7 new transits of the “hot Jupiter” WASP-5b using a 61 cm telescope located in New Zealand, in order to search for transit timing variations (TTVs), which can be induced by additional bodies existing in the system. Combining them with other available photometric and radial velocity (RV) data, we find that its transit timings do not match a linear ephemeris; the best-fit $\chi^2$ value is 32.2 with 9 degrees of freedom, which corresponds to a confidence level of 99.982% or 3.7 $\sigma$. This result indicates that excess variations of transit timings have been observed, either due to unknown systematic effects, or possibly due to real TTVs. The TTV amplitude is as large as 50 s, and if this is real it cannot be explained by some effect other than an additional body, or bodies. From RV data, we put an upper limit on the RV amplitude caused by a possible secondary body (planet) as 21 m s$^{-1}$, which corresponds to its mass of 22–70$\ M_{\oplus}$ over the orbital period ratio of the two planets from 0.2 to 5.0. From the TTV data, using numerical simulations, we narrowed the limits down to 2$\ M_{\oplus}$ near 1:2 and 2:1 mean-motion resonances (MMRs) with WASP-5b at the 3$\sigma$ level, assuming that the two planets are co-planer. We also put an upper limit of 43$\ M_{\oplus}$ (3$\sigma$) on excess of Trojan mass using both RV and photometric data. We also find that if the orbit of the possible secondary planet is a circle or an ellipse of small eccentricity, it would be likely an orbit near that of low-order MMRs.