Discovery and characterization of two Neptune-mass planets orbiting HD 212729 with TESS
Torres, Guillermo; Latham, David W.; Wheatley, Peter J.; Stassun, Keivan G.; Bayliss, Daniel; Howell, Steve B.; Seager, Sara; Winn, Joshua N.; Jenkins, Jon M.; Anderson, David R.; Armstrong, David J.; Osborn, Ares; Twicken, Joseph D.; Bouchy, François; Nielsen, Louise D.; Osborn, Hugh P.; Sousa, Sérgio G.; Christiansen, Jessie L.; Lillo-Box, Jorge; Burke, Christopher J.; Adibekyan, Vardan; Delgado-Mena, Elisa; Hojjatpanah, Saeed; Hoyer, Sergio; Knierim, Henrik; Veras, Dimitri; Dumusque, Xavier; Keniger, Marcelo Aron Fetzner; Hadjigeorghiou, Andreas; Hawthorn, Faith; Helled, Ravit; Rodrigues, José; Rodriguez, David; Santos, Nuno C.; Strøm, Paul A.; Udry, Stephane
United Kingdom, Portugal, France, United States, Switzerland, Spain, Germany
Abstract
We report the discovery of two exoplanets orbiting around HD 212729 (TOI 1052, TIC 317060587), a Teff = 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 $2.87^{+0.29}_{-0.24}$ R⊕, a mass of 16.9 ± 1.7 M⊕, 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 $34.3^{+4.1}_{-3.7}$ M⊕ 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 $0.18^{+0.09}_{-0.07}$ for planet b and $0.24^{+0.09}_{-0.08}$ 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 $3.9^{+1.7}_{-1.3}$ 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 $\scriptstyle \sim$1500 au, making this a potential wide binary star system.