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

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

Abstract

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.

Additional Information

© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2022 April 12; revised 2022 May 29; accepted 2022 June 9; published 2022 July 27. Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We thank Zhoujian Zhang for discussions about bolometric correction, Michiko Fujii for stellar encounters in open clusters, and Brendan Bowler for the companion of 1RXS J034231.8+121622. This work has made use of data from the European Space Agency (ESA) mission Gaia (Gaia Collaboration et al. 2016; https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. For the Keck-II/NIRC2 data (P.I. T. Currie), this research has made use of the Keck Observatory Archive (KOA), which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with the National Aeronautics and Space Administration. This work has benefited from The UltracoolSheet, maintained by Will Best, Trent Dupuy, Michael Liu, Rob Siverd, and Zhoujian Zhang, and developed from compilations by Dupuy & Liu (2012), Dupuy & Kraus (2013), Liu et al. (2016), Best et al. (2018), and Best et al. (2021). This research has benefited from the Montreal Brown Dwarf and Exoplanet Spectral Library, maintained by Jonathan Gagné. This research has made use of the SIMBAD and VizieR services, both operated at Centre de Données astronomiques de Strasbourg (CDS, https://cds.u-strasbg.fr/) in France, and NASA's Astrophysics Data System Bibliographic Services. IRAF is distributed by the National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. Part of the data analysis was carried out on the Multi-wavelength Data Analysis System operated by the Astronomy Data Center (ADC), National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the universe from Maunakea, which has cultural, historical, and natural significance in Hawaii. We appreciate the critical support from all the current and recent Subaru and Keck Observatory staff. Their support was essential in achieving this discovery, especially amidst the many difficulties associated with the COVID-19 pandemic. We thank the Subaru and NASA Keck Time Allocation Committees for their generous support of this program. T.C. was supported by a NASA Senior Postdoctoral Fellowship and NASA/Keck grant LK-2663-948181. T.B. gratefully acknowledges support from the Heising-Simons Foundation and from NASA under grant No. 80NSSC18K0439. V.D. and N.S. were supported by the NASA grant Nos. 80NSSC19K0336. K.A. also gratefully acknowledges support from the Heising-Simons Foundataion. K.W. acknowledges support from NASA through the NASA Hubble Fellowship grant HST-HF2-51472.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. The results reported herein benefited from collaborations and/or information exchange within NASA's Nexus for Exoplanet System Science (NExSS) research coordination network sponsored by NASA's Science Mission Directorate. M.T. is supported by JSPS KAKENHI grant No. 18H05442, and E.A. is supported by MEXT/JSPS KAKENHI grant No. 17K05399. The development of SCExAO was supported by JSPS (Grant-in-Aid for Research Nos. 23340051, 26220704, 23103002, and 21H04998), Astrobiology Center of NINS, the Mt Cuba Foundation, and the director's contingency fund at Subaru Telescope. CHARIS was developed under the support of the Grant-in-Aid for Scientific Research on Innovative Areas No. 2302. The Okayama 188 cm telescope is operated by a consortium led by the Exoplanet Observation Research Center, Tokyo Institute of Technology (Tokyo Tech), under the framework of tripartite cooperation among Asakuchi-city, NAOJ, and Tokyo Tech. This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Facility: the Subaru Telescope (SCExAO, CHARIS), Keck:II (NIRC2). Software: astropy (Astropy Collaboration et al. 2013, 2018), BANYAN-Σ (Gagné et al. 2018), CHARIS-DRP (Brandt et al. 2017), CHARIS-DPP (https://github.com/thaynecurrie/charis-dpp, Currie et al. 2020b), orvara (Brandt et al. 2021), IRAF : (Tody et al. 1986, 1993), matplotlib (Hunter 2007), numpy (van der Walt et al. 2011), scipy (Virtanen et al. 2020), sympy (Meurer et al. 2017), pandas (McKinney 2010), Google Colaboratory.

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