The Astronomical Journal (Jan 2024)

The TESS-Keck Survey. VII. A Superdense Sub-Neptune Orbiting TOI-1824

  • Sarah Lange,
  • Joseph M. Akana Murphy,
  • Natalie M. Batalha,
  • Ian J. M. Crossfield,
  • Courtney D. Dressing,
  • Benjamin Fulton,
  • Andrew W. Howard,
  • Daniel Huber,
  • Howard Isaacson,
  • Stephen R. Kane,
  • Erik A. Petigura,
  • Paul Robertson,
  • Lauren M. Weiss,
  • Aida Behmard,
  • Corey Beard,
  • Sarah Blunt,
  • Casey L. Brinkman,
  • Ashley Chontos,
  • Fei Dai,
  • Paul A. Dalba,
  • Tara Fetherolf,
  • Steven Giacalone,
  • Michelle L. Hill,
  • Rae Holcomb,
  • Jack Lubin,
  • Mason G. MacDougall,
  • Andrew W. Mayo,
  • Teo Močnik,
  • Daria Pidhorodetska,
  • Alex S. Polanski,
  • Malena Rice,
  • Lee J. Rosenthal,
  • Ryan A. Rubenzahl,
  • Nicholas Scarsdale,
  • Emma V. Turtelboom,
  • Judah Van Zandt,
  • David R. Ciardi,
  • Andrew W. Boyle

DOI
https://doi.org/10.3847/1538-3881/ad34d9
Journal volume & issue
Vol. 167, no. 6
p. 282

Abstract

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We confirm a massive sub-Neptune-sized planet on a P = 22.8 days orbit around the star TOI-1824 ( T _eff = 5200 K, V = 9.7 mag). TESS first identified TOI-1824 b (formerly TOI-1824.01) as an object of interest in 2020 April after two transits in Sector 22 were matched with a single transit in Sector 21. TOI-1824 was subsequently targeted for ground-based Doppler monitoring with Keck-HIRES and APF-Levy. Using a joint model of the TESS photometry, radial velocities, and Ca ii H and K emission measurements as an activity indicator, we find that TOI-1824 b is an unusually dense sub-Neptune. The planet has a radius R _p = 2.63 ± 0.15 R _⊕ and mass M _p = 18.5 ± 3.2 M _⊕ , implying a bulk density of 5.6 ± 1.4 g cm ^−3 . TOI-1824 b's mass and radius situate it near a small group of “superdense sub-Neptunes” ( R _p ≲ 3 R _⊕ and M _p ≳ 20 M _⊕ ). While the formation mechanism of superdense sub-Neptunes is a mystery, one possible explanation is the constructive collision of primordial icy cores; such giant impacts would drive atmospheric escape and could help explain these planets' apparent lack of massive envelopes. We discuss TOI-1824 b in the context of these overdense planets, whose unique location in the exoplanet mass–radius plane make them a potentially valuable tracer of planet formation.

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