NGTS-8b and NGTS-9b: two non-inflated hot-Jupiters

TL;DR

This paper reports the discovery and characterization of two non-inflated hot-Jupiters, NGTS-8b and NGTS-9b, providing detailed planetary parameters and comparing their radii with theoretical models.

Contribution

First detailed characterization of two non-inflated hot-Jupiters, confirming their radii align with non-inflated planetary models.

Findings

NGTS-8b has a mass of 0.93 MJ and radius of 1.09 RJ.

NGTS-9b has a mass of 2.90 MJ and radius of 1.07 RJ.

Both planets' radii agree with non-inflated theoretical models.

Abstract

We report the discovery, by the Next Generation Transit Survey (NGTS), of two hot-Jupiters NGTS-8b and NGTS-9b. These orbit a V = 13.68 K0V star (Teff = 5241 +/- 50 K) with a period of 2.49970 days, and a V = 12.80 F8V star (Teff = 6330 +/- 130 K) in 4.43527 days, respectively. The transits were independently verified by follow-up photometric observations with the SAAO 1.0-m and Euler telescopes, and we report on the planetary parameters using HARPS, FEROS and CORALIE radial velocities. NGTS-8b has a mass, 0.93 +0.04 -0.03 MJ and a radius, 1.09 +/- 0.03 RJ similar to Jupiter, resulting in a density of 0.89 +0.08 -0.07 g cm-3. This is in contrast to NGTS-9b, which has a mass of 2.90 +/- 0.17 MJ and a radius of 1.07 +/- 0.06 RJ , resulting in a much greater density of 2.93 +0.53 -0.49 g cm-3. Statistically, the planetary parameters put both objects in the regime where they would be expected to exhibit larger than predicted radii. However, we find that their radii are in agreement with predictions by theoretical non-inflated models.