NGTS-5b: a highly inflated planet offering insights into the sub-Jovian desert^★

¹ Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
e-mail: philipp.eigmueller@dlr.de
² Center for Astronomy and Astrophysics, TU Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
³ Institute of Geological Sciences, FU Berlin, Malteserstr. 74–100, 12249 Berlin, Germany
⁴ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁵ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁶ Department of Physics and Astronomy, Leicester Institute of Space and Earth Observation, University of Leicester, LE1 7RH, UK
⁷ Astrophysics Group, Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
⁸ Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
⁹ Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago, Chile
¹⁰ Centro de Astrofísica y Tecnologías Afines (CATA), Casilla 36-D, Santiago, Chile
¹¹ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, BT7 1NN Belfast, UK
¹² Instituto de Astronomía, Universidad Católica del Norte, Angamos 0610, 1270709 Antofagasta, Chile
¹³ Leibniz Institute for Astrophysics Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
¹⁴ Institute for Physics and Astronomy, University of Potsdam, Campus Golm, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
¹⁵ Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK

Received: 5 February 2019
Accepted: 25 April 2019

Abstract

Context. Planetary population analysis gives us insight into formation and evolution processes. For short-period planets, the sub-Jovian desert has been discussed in recent years with regard to the planet population in the mass/period and radius/period parameter space without taking stellar parameters into account. The Next Generation Transit Survey (NGTS) is optimised for detecting planets in this regime, which allows for further analysis of the sub-Jovian desert.

Aims. With high-precision photometric surveys (e.g. with NGTS and TESS), which aim to detect short period planets especially around M/K-type host stars, stellar parameters need to be accounted for when empirical data are compared to model predictions. Presenting a newly discovered planet at the boundary of the sub-Jovian desert, we analyse its bulk properties and use it to show the properties of exoplanets that border the sub-Jovian desert.

Methods. Using NGTS light curve and spectroscopic follow-up observations, we confirm the planetary nature of planet NGTS-5b and determine its mass. Using exoplanet archives, we set the planet in context with other discoveries.

Results. NGTS-5b is a short-period planet with an orbital period of 3.3569866 ± 0.0000026 days. With a mass of 0.229 ± 0.037 M_Jup and a radius of 1.136 ± 0.023 R_Jup, it is highly inflated. Its mass places it at the upper boundary of the sub-Jovian desert. Because the host is a K2 dwarf, we need to account for the stellar parameters when NGTS-5b is analysed with regard to planet populations.

Conclusions. With red-sensitive surveys (e.g. with NGTS and TESS), we expect many more planets around late-type stars to be detected. An empirical analysis of the sub-Jovian desert should therefore take stellar parameters into account.