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Journal Articles Monthly Notices of the Royal Astronomical Society Year : 2023

NGTS-21b: an inflated Super-Jupiter orbiting a metal-poor K dwarf

Douglas R. Alves
  • Function : Author
James S. Jenkins
  • Function : Author
Jose I. Vines
  • Function : Author
Louise D. Nielsen
  • Function : Author
Samuel Gill
  • Function : Author
Jack S. Acton
  • Function : Author
D. R. Anderson
  • Function : Author
Daniel Bayliss
  • Function : Author
François Bouchy
Hannes Breytenbach
  • Function : Author
Edward M. Bryant
  • Function : Author
Matthew R. Burleigh
  • Function : Author
Sarah L. Casewell
  • Function : Author
Philipp Eigmüller
  • Function : Author
Edward Gillen
  • Function : Author
Michael R. Goad
  • Function : Author
Maximilian N. Günther
  • Function : Author
Beth A. Henderson
  • Function : Author
Alicia Kendall
  • Function : Author
Monika Lendl
  • Function : Author
Maximiliano Moyano
  • Function : Author
Ramotholo R. Sefako
  • Function : Author
Alexis M. S. Smith
  • Function : Author
Rosanne H. Tilbrook
  • Function : Author
Jessymol K. Thomas
  • Function : Author
Stéphane Udry
  • Function : Author
Christopher A. Watson
  • Function : Author
Richard G. West
  • Function : Author
Peter J. Wheatley
  • Function : Author
Hannah L. Worters
  • Function : Author
Ares Osborn
  • Function : Author

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.
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Dates and versions

insu-03863219 , version 1 (23-03-2023)

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Douglas R. Alves, James S. Jenkins, Jose I. Vines, Louise D. Nielsen, Samuel Gill, et al.. NGTS-21b: an inflated Super-Jupiter orbiting a metal-poor K dwarf. Monthly Notices of the Royal Astronomical Society, 2023, 517, pp.4447-4457. ⟨10.1093/mnras/stac2884⟩. ⟨insu-03863219⟩
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