NGTS-13b: a hot 4.8 Jupiter-mass planet transiting a subgiant star^★

¹ Observatoire de Genève, Université de Genève, Chemin Pegasi 51b, 1290 Sauverny, Switzerland
e-mail: Nolan.Grieves@unige.ch
² Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
³ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
⁴ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
⁵ Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
⁶ School of Physics and Astronomy, University of Leicester, LE1 7RH, UK
⁷ Center for Astronomy and Astrophysics, TU Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
⁸ Astronomy Unit, Queen Mary University of London, Mile End Road, London E1 4NS, UK
⁹ Astrophysics Group, Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
¹⁰ Department of Physics, Kavli Institute for Astrophysics and Space Research, MIT, 77 Mass. Ave, Cambridge, MA 02139, USA
¹¹ Centro de Astrofísica y Tecnologías Afines (CATA), Casilla 36-D, Santiago, Chile
¹² Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Av. Diagonal las Torres 2640, Peñalolén, Santiago, Chile
¹³ Millennium Institute for Astrophysics, Santiago, Chile
¹⁴ Instituto de Astronomía, Universidad Católica del Norte, Angamos 0610, 1270709 Antofagasta, Chile

Received: 2 October 2020
Accepted: 6 January 2021

Abstract

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 ± 73 K, M_* = 1.30_−0.18^+0.11 M_⊙, and R_* = 1.79 ± 0.06 R_⊙. 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 ± 0.046 R_Jup, a mass of M_P = 4.84 ± 0.44 M_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 4 M_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.