NGTS-21b: an inflated Super-Jupiter orbiting a metal-poor K dwarf
Abstract
We report the discovery of NGTS-21b , a massive hot Jupiter orbiting a low-mass star as part of the Next Generation Transit Survey (NGTS). The planet has a mass and radius of 2.36 ± 0.21 MJ and 1.33 ± 0.03 RJ, and an orbital period of 1.543 d. The host is a K3V (Teff = 4660 ± 41 K) metal-poor ([Fe/H] = -0.26 ± 0.07 dex) dwarf star with a mass and radius of 0.72 ± 0.04 M⊙ and 0.86 ± 0.04R⊙. Its age and rotation period of $10.02^{+3.29}_{-7.30}$ Gyr and 17.88 ± 0.08 d, respectively, are in accordance with the observed moderately low-stellar activity level. When comparing NGTS-21b with currently known transiting hot Jupiters with similar equilibrium temperatures, it is found to have one of the largest measured radii despite its large mass. Inflation-free planetary structure models suggest the planet's atmosphere is inflated by $\sim \! 21{{\ \rm per\ cent}}$, while inflationary models predict a radius consistent with observations, thus pointing to stellar irradiation as the probable origin of NGTS-21b's radius inflation. Additionally, NGTS-21b's bulk density (1.25 ± 0.15 g cm-3) is also amongst the largest within the population of metal-poor giant hosts ([Fe/H] < 0.0), helping to reveal a falling upper boundary in metallicity-planet density parameter space that is in concordance with core accretion formation models. The discovery of rare planetary systems such as NGTS-21 greatly contributes towards better constraints being placed on the formation and evolution mechanisms of massive planets orbiting low-mass stars.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- December 2022
- DOI:
- 10.1093/mnras/stac2884
- arXiv:
- arXiv:2210.01027
- Bibcode:
- 2022MNRAS.517.4447A
- Keywords:
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- techniques: photometric;
- techniques: radial velocities;
- planets and satellites: detection;
- planets and satellites: fundamental parameters;
- planets and satellites: general;
- stars: general;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- 12 pages, 13 figures, accepted for publication in MNRAS