Abstract
We report the discovery of the massive hot Jupiter NGTS-13b by the Next Generation Transit Survey (NGTS). The V = 12.7 host star is likely in the subgiant evolutionary phase with logg* = 4.04 ± 0.05, Teff = 5819 ± 73 K, M* = 1.30−0.18+0.11 M⊙, and R* = 1.79 ± 0.06 R⊙. The NGTS detected a transiting planet with a period of P = 4.12 days around the star, which was later validated with the Transiting Exoplanet Survey Satellite (TESS; TIC 454069765). We confirm the planet using radial velocities from the CORALIE spectrograph. Using NGTS and TESS full-frame image photometry combined with CORALIE radial velocities, we determine NGTS-13b to have a radius of RP = 1.142 ± 0.046 RJup, a mass of MP = 4.84 ± 0.44 MJup, and an eccentricity of e = 0.086 ± 0.034. Previous studies have suggested that ~4 MJup may be the border separating two formation scenarios (e.g., core accretion and disk instability) and that massive giant planets share similar formation mechanisms as lower-mass brown dwarfs. NGTS-13b is just above 4 MJup, making it an important addition to the statistical sample needed to understand the differences between various classes of substellar companions. The high metallicity of NGTS-13, [Fe/H] = 0.25 ± 0.17, does not support previous suggestions that massive giants are found preferentially around lower metallicity host stars, but NGTS-13b does support findings that more massive and evolved hosts may have a higher occurrence of close-in massive planets than lower-mass unevolved stars.
Highlights
There are two mechanisms proposed for giant planet formation in general: gravitational instability – through its own selfgravity the protoplanetary disk fragments into giant gaseous protoplanets that contract and collapse to form giant planets (e.g., Boss 1997), and core accretion – planetesimal collisions form rocky protoplanet cores that accrete gas from the protoplanetary disk (e.g., Pollack et al 1996)
Our analysis finds Next Generation Transit Survey (NGTS)-13b to have a mass of 4.84 ± 0.44 MJup and radius of 1.142 ± 0.046 RJup at a short 4.12 day orbital period yielding an equilibrium temperature of 1605 ± 30 K, making NGTS-13b a massive hot Jupiter
NGTS-13b has a typical radius compared to planets with similar masses suggesting that even with its high equilibrium temperature it is not significantly affected by bloating, which is expected for massive planets (Sestovic et al 2018)
Summary
There are two mechanisms proposed for giant planet formation in general: gravitational instability – through its own selfgravity the protoplanetary disk fragments into giant gaseous protoplanets that contract and collapse to form giant planets (e.g., Boss 1997), and core accretion – planetesimal collisions form rocky protoplanet cores that accrete gas from the protoplanetary disk (e.g., Pollack et al 1996). Another proposed mechanism for migration is high-eccentricity tidal migration, where a giant planet has orbital angular momentum extracted from it by a perturber, pushing the planet to a highly elliptical orbit, the planet reduces its orbital energy through tidal interactions with the central star causing it to circularize into a close-in orbit (e.g., Rasio & Ford 1996) These various formation theories should have differing effects on the characteristics of hot Jupiters. We present the discovery of a massive hot Jupiter orbiting a subgiant star This planet was first detected by NGTS, subsequently verified by the space-based all-sky Transiting Exoplanet Survey Satellite (TESS; Ricker et al 2015), and confirmed through follow-up RV measurements with the CORALIE (Queloz et al 2001) spectrograph.
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