Discovery and characterization of two Neptune-mass planets orbiting HD 212729 with TESS

We report the disco v ery of two exoplanets orbiting around HD 212729 (TOI 1052, TIC 317060587), a T-eff = 6146 K star with V = 9.51 observed by TESS in Sectors 1 and 13. One exoplanet, TOI-1052b, is Neptune-mass and transits the star, and an additional planet TOI-1052c is observed in radial velocities but not seen to transit. We confirm the planetary nature of TOI-1052b using precise radial velocity observations from HARPS and determined its parameters in a joint RV and photometry analysis. TOI-1052b has a radius of 2.87(-0.24)(+0.29) R-circle plus, a mass of 16.9 +/- 1.7 M-circle plus, and an orbital period of 9.14 d. TOI-1052c does not show any transits in the TESS data, and has a minimum mass of 34.3(-3.7)(+4.1) M-circle plus and an orbital period of 35.8 d, placing it just interior to the 4:1 mean-motion resonance. Both planets are best fit by relatively high but only marginally significant eccentricities of 0.18(-0.07)(+0.09) for planet b and 0.24(-0.08)(+0.09) for planet c. We perform a dynamical analysis and internal structure model of the planets as well as deriving stellar parameters and chemical abundances. The mean density of TOI-1052b is 3.9(-1.3)(+ 1.7) g cm(-3) consistent with an internal structure similar to Neptune. A nearby star is observed in Gaia DR3 with the same distance and proper motion as TOI-1052, at a sky projected separation of similar to 1500 au, making this a potential wide binary star system.

Automated summary

We report the discovery of two exoplanets orbiting around HD 212729 (TOI 1052, TIC 317060587), a star with T-eff = 6146 K and V = 9.51. One exoplanet, TOI-1052b, is Neptune-mass and transits the star, and an additional planet TOI-1052c is observed through radial velocities but not seen to transit. The parameters of TOI-1052b are determined using precise radial velocity observations from HARPS.