NGTS 15b, 16b, 17b and 18b: four hot Jupiters from the Next Generation Transit Survey

TL;DR

This paper reports the discovery of four new hot Jupiters from the NGTS, analyzing their properties, irradiation levels, and inflation, and discusses the challenges in modeling planetary inflation mechanisms.

Contribution

The discovery of four hot Jupiters from NGTS and an analysis of their inflation status, highlighting the need for improved models with additional parameters.

Findings

All four planets are highly irradiated and likely inflated.

NGTS-16b, NGTS-17b, and NGTS-18b are probably inflated, but models show disparities.

Current inflationary models lack key parameters to fully explain observed inflation.

Abstract

We report the discovery of four new hot Jupiters with the Next Generation Transit Survey (NGTS). NGTS-15b, NGTS-16b, NGTS-17b, and NGTS-18b are short-period ($P<5$d) planets orbiting G-type main sequence stars, with radii and masses between $1.10-1.30$ $R_J$ and $0.41-0.76$ $M_J$. By considering the host star luminosities and the planets' small orbital separations ($0.039-0.052$ AU), we find that all four hot Jupiters are highly irradiated and therefore occupy a region of parameter space in which planetary inflation mechanisms become effective. Comparison with statistical studies and a consideration of the planets' high incident fluxes reveals that NGTS-16b, NGTS-17b, and NGTS-18b are indeed likely inflated, although some disparities arise upon analysis with current Bayesian inflationary models. However, the underlying relationships which govern radius inflation remain poorly understood. We postulate that the inclusion of additional hyperparameters to describe latent factors such as heavy element fraction, as well as the addition of an updated catalogue of hot Jupiters, would refine inflationary models, thus furthering our understanding of the physical processes which give rise to inflated planets.