Orbit Refinement of WASP-18 b and Evidence Against the Existence of WASP-18 c

We present an updated transit ephemeris for the exoplanet WASP-18 b and critically examine the existence of a proposed second planet, WASP-18 c. Using 205 transit light curves from TESS, CHEOPS, Exoplanet Watch, Exoplanet Transit Database and previous literature, we derive a refined mid-transit time of 2460933.096346 +/- 0.000022 BJD TDB and an orbital period of 0.94145252 +/- 1.1 x 10-8 days for WASP-18 b. Our forward-propagated ephemeris to January 1, 2030, shows a timing uncertainty of 2.41 seconds. This high-precision refinement serves as a robust baseline to test for Transit Timing Variations (TTVs), ensuring that any reported deviations are not artifacts of an insufficiently constrained orbital period. In addition, we analyze 449 radial velocity (RV) measurements from the CORALIE, HARPS, PFS, HIRES and ESPRESSO spectrographs to search for signatures of WASP-18 c, a previously proposed additional planetary companion, and also estimated the k2 love number as 0.62199 +/- 0.0011. However, we do not find significant variations in either transit timing or RV data that support the presence of WASP-18 c. Moreover, the most significantly identified periodicities are not consistently measured across the transit or RV datasets, strongly arguing against the existence of a dynamically relevant second planet in the system. Our results indicate that the claimed WASP-18 c signal is likely spurious in nature. Overall, this work enhances our understanding of the WASP-18 system and provides a valuable resource for future observational campaigns with the refinement of the b planet orbit and falsified status of the previously defined c planet.