Revisiting WASP-47 with ESPRESSO and TESS

Abstract: WASP-47 hosts a remarkable planetary system containing a hot Jupiter (WASP-47 b; P = 4.159 days) with an inner super-Earth (WASP-47 e; P = 0.7896 days), a close-orbiting outer Neptune (WASP-47 d; P = 9.031 days), and a long period giant planet (WASP-47 c; P = 588.4 days). We use the new TESS photometry to refine the orbital ephemerides of the transiting planets in the system, particularly the hot Jupiter WASP-47 b, for which we find an update equating to a 17.4 min shift in the transit time. We report new radial velocity measurements from the ESPRESSO spectrograph for WASP-47, which we use to refine the masses of WASP-47 d and WASP-47 e, with a high cadence observing strategy aimed to focus on the super-Earth WASP-47 e. We detect a periodic modulation in the K2 photometry that corresponds to a 32.5$\pm$3.9 day stellar rotation, and find further stellar activity signals in our ESPRESSO data consistent with this rotation period. For WASP-47 e we measure a mass of 6.77$\pm$0.57 M$_{\oplus}$ and a bulk density of 6.29$\pm$0.60 gcm$^{-3}$, giving WASP-47 e the second most precisely measured density to date of any super-Earth. The mass and radius of WASP-47 e, combined with the exotic configuration of the planetary system, suggest the WASP-47 system formed through a mechanism different to systems with multiple small planets or more typical isolated hot Jupiters.