2021A&A...647A.180G

We report the discovery of the massive hot Jupiter NGTS-13b by the Next Generation Transit Survey (NGTS). The V=12.7 host star is likely in the subgiant evolutionary phase with logg_*=4.04±0.05, T_eff=5819±73K, M_*=1.30_–0.18^+0.11M_☉, and R_*=1.79± 0.06R_☉. The NGTS detected a transiting planet with a period of P=4.12 days around the star, which was later validated with the Transiting Exoplanet Survey Satellite (TESS; TIC 454069765). We confirm the planet using radial velocities from the CORALIE spectrograph. Using NGTS and TESS full-frame image photometry combined with CORALIE radial velocities, we determine NGTS-13b to have a radius of R_P=1.142±0.046R_Jup, a mass of M_P=4.84±0.44M_Jup, and an eccentricity of e=0.086±0.034. Previous studies have suggested that ∼4 M_Jup may be the border separating two formation scenarios (e.g., core accretion and disk instability) and that massive giant planets share similar formation mechanisms as lower-mass brown dwarfs. NGTS-13b is just above 4M_Jup, making it an important addition to the statistical sample needed to understand the differences between various classes of substellar companions. The high metallicity of NGTS-13, [Fe/H]=0.25±0.17, does not support previous suggestions that massive giants are found preferentially around lower metallicity host stars, but NGTS-13b does support findings that more massive and evolved hosts may have a higher occurrence of close-in massive planets than lower-mass unevolved stars.