Direct-imaging Discovery and Dynamical Mass of a Substellar Companion Orbiting an Accelerating Hyades Sun-like Star with SCExAO/CHARIS

Masayuki Kuzuhara, Thayne Currie, Takuya Takarada, Timothy D. Brandt, Bun’ei Sato, Taichi Uyama, Markus Janson, Jeffrey Chilcote, Taylor Tobin, Kellen Lawson, Yasunori Hori, Olivier Guyon, Tyler D. Groff, Julien Lozi, Sebastien Vievard, Ananya Sahoo, Vincent Deo, Nemanja Jovanovic, Kyohoon Ahn, Frantz MartinacheNour Skaf, Eiji Akiyama, Barnaby R. Norris, Mickaël Bonnefoy, Krzysztof G. Hełminiak, Tomoyuki Kudo, Michael W. McElwain, Matthias Samland, Kevin Wagner, John Wisniewski, Gillian R. Knapp, Jungmi Kwon, Jun Nishikawa, Eugene Serabyn, Masahiko Hayashi, Motohide Tamura

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


We present the direct-imaging discovery of a substellar companion in orbit around a Sun-like star member of the Hyades open cluster. So far, no other substellar companions have been unambiguously confirmed via direct imaging around main-sequence stars in Hyades. The star HIP 21152 is an accelerating star as identified by the astrometry from the Gaia and Hipparcos satellites. We detected the companion, HIP 21152 B, in multiple epochs using the high-contrast imaging from SCExAO/CHARIS and Keck/NIRC2. We also obtained the stellar radial-velocity data from the Okayama 188 cm telescope. The CHARIS spectroscopy reveals that HIP 21152 B’s spectrum is consistent with the L/T transition, best fit by an early T dwarf. Our orbit modeling determines the semimajor axis and the dynamical mass of HIP 21152 B to be 17.5 − 3.8 + 7.2 au and 27.8 − 5.4 + 8.4 M Jup, respectively. The mass ratio of HIP 21152 B relative to its host is ≈2%, near the planet/brown dwarf boundary suggested by recent surveys. Mass estimates inferred from luminosity-evolution models are slightly higher (33-42 M Jup). With a dynamical mass and a well-constrained age due to the system’s Hyades membership, HIP 21152 B will become a critical benchmark in understanding the formation, evolution, and atmosphere of a substellar object as a function of mass and age. Our discovery is yet another key proof of concept for using precision astrometry to select direct-imaging targets.

Original languageEnglish (US)
Article numberL19
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Aug 1 2022

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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