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Publication Detail
NGTS-21b: An Inflated Super-Jupiter Orbiting a Metal-poor K dwarf
  • Publication Type:
    Journal article
  • Publication Sub Type:
  • Authors:
    Alves DR, Jenkins JS, Vines JI, Nielsen LD, Gill S, Acton JS, Anderson DR, Bayliss D, Bouchy F, Breytenbach H, Bryant EM, Burleigh MR, Casewell SL, Eigmüller P, Gillen E, Goad MR, Günther MN, Henderson BA, Kendall A, Lendl M, Moyano M, Sefako RR, Smith AMS, Costes JC, Tilbrook RH, Thomas JK, Udry S, Watson CA, West RG, Wheatley PJ, Worters HL, Osborn A
  • Publisher:
    Oxford University Press (OUP)
  • Publication date:
  • Journal:
    Monthly Notices of the Royal Astronomical Society
  • Status:
  • Print ISSN:
  • Language:
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 days. 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 ± 0.04 R⊙. 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 $\sim 21\%$, 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/cm3) 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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