TIC-65910228 b / NGTS-38 b, a 180 day transiting warm super-Jupiter

TL;DR

This paper reports the discovery and detailed characterization of NGTS-38 b, a long-period, warm super-Jupiter orbiting a bright star, using combined photometric and spectroscopic observations, contributing to the understanding of such exoplanets.

Contribution

It presents the first detailed characterization of a long-period warm super-Jupiter with multi-method observations, expanding the known population of such exoplanets.

Findings

Discovered a 180-day period super-Jupiter with a radius of 1.08 R_J and mass of 4.78 M_J.

Confirmed the planet's orbit and mass through combined TESS, NGTS, CORALIE, and HARPS data.

Identified NGTS-38 b as one of the longest-period warm-Jupiters with a well-characterized transiting orbit.

Abstract

We present the discovery of TIC-65910228 b / NGTS-38 b, a giant exoplanet with a radius of $1.081\pm0.047$ R$_\text{J}$ and a mass of $4.78_{-0.37}^{+0.40}$ M$_\text{J}$ on a long-period ($180.52791\pm0.00038$ day), moderately eccentric ($e=0.308\pm0.011$) orbit transiting a bright (V=$10.230\pm0.020$ mag) metal rich ([Fe/H]=$0.33\pm0.09$, 'dex') F6V-F7V type host star. The planet was initially detected from a single transit in TESS Sector 33. A photometric monitoring campaign of 228 nights with NGTS detected a transit egress of the planet, which together with spectroscopic radial velocity monitoring with CORALIE and HARPS identified an orbital period of ~180.5,d. These radial velocity measurements also showed the mass of the companion to be planetary. Additional transit observations coordinated by the TESS follow-up observing program allowed further confirmation and refinement of this period. With its relatively cool equilibrium temperature of $458\pm11$ K, NGTS-38 b joins a small but growing population of well characterised transiting warm-Jupiters and has one of the longest periods of any discovered to date. The target is situated in the LOPS2 field of the upcoming PLATO mission which will allow for greater refinement of the system parameters and potential for the discovery of additional companions too small and/or too long-period to be seen by TESS or NGTS. NGTS-38 b's bright host star and wide orbital separation make it an attractive target for further study, including potential measurement of its spin-orbit alignment or targeted exomoon/ring searches.