2020A&A...636A..98C

We present 22 new transit observations of the exoplanets WASP-18Ab, WASP-19b, and WASP-77Ab, from the Transit Monitoring in the South project. We simultaneously model our newly collected transit light curves with archival photometry and radial velocity data to obtain refined physical and orbital parameters. We include TESS light curves of the three exoplanets to perform an extended analysis of the variations in their transit mid-time (TTV) and to refine their planetary orbital ephemeris. We did not find significant TTV_RMS variations larger than 47, 65, and 86 s for WASP-18Ab, WASP-19b, and WASP-77Ab, respectively. Dynamical simulations were carried out to constrain the masses of a possible perturber. The observed mean square (RMS) could be produced by a perturber body with an upper limit mass of 9, 2.5, 11 and 4M_⊕ in 1:2, 1:3, 2:1, and 3:1 resonances in the WASP-18Ab system. In the case of WASP-19b, companions with masses up to 0.26, 0.65, 1, and 2.8M_⊕, in 1:2, 2:1, 3:1, and 5:3 resonances respectively, produce the RMS. For the WASP-77Ab system, this RMS could be produced by a planet with mass in the range of 1.5-9M_⊕ in 1:2, 1:3, 2:1, 2:3, 3:1, 3:5, or 5:3 resonances. Comparing our results with RV variations, we discard massive companions with 350M_⊕ in 17:5 resonance for WASP-18Ab, 95M_⊕ in 4:1 resonance for WASP-19b, and 105M_⊕ in 5:2 resonance for WASP-77Ab. Finally, using a Lomb-Scargle period search we find no evidence of a periodic trend on our TTV data for the three exoplanets.