NGTS-8b and NGTS-9b: two non-in ated hot-Jupiters

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 (T-eff = 5241 +/- 50 K) with a period of 2.49970 d, and a V = 12.80 F8V star (T-eff = 6330 +/- 130 K) in 4.43527 d, respectively. The transits were independently verified by follow-up photometric observations with the South African Astronomical Observatory 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(-0.03)(+0.04)M(J) and a radius, 1.09 +/- 0.03 R-J similar to Jupiter, resulting in a density of 0.89(-0.07)(+0.08) g cm(-3). This is in contrast to NGTS-9b, which has a mass of 2.90 +/- 0.17M(J) and a radius of 1.07 +/- 0.06 R-J, resulting in a much greater density of 2.93(-0.49)(+0.53) 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.