HD224018 HARPS-N data

The system turned out to be more crowded than shown by K2. Radial velocities revealed the presence of two additional bodies: a candidate cold companion on an eccentric orbit with a minimum mass nearly half that of Jupiter (eccentricity 0.60^+0.07^_-0.08); semi-major axis 8.6^+1.5^_-1.6_au), and an innermost super-Earth (orbital period 10.6413+/-0.0028d; mass 4.1+/-0.8M_{Earth}_) for which we discovered previously undetected transit events in K2 photometry.

TESS data revealed a second transit of one of the two companions originally observed by K2. This allowed us to constrain its orbital period to a grid of values, the most likely being nearly 138 days, which would imply a mass less than 9M_{Earth}_, at a 3-sigma significance level. Given the level of precision of our measurements, we were able to constrain the internal structure and composition of the second-most distant planet from the host star, a warm sub-Neptune with a bulk density of 3.9+/-0.5g/cm^3^.

HD 224018 hosts three close-in transiting planets in the super-Earth-to- sub-Neptune regime, and a candidate cold and eccentric massive companion. Additional follow-up is needed to better characterise the physical properties of the planets and their architecture, and to study the evolutionary history of the system.