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Published November 2025 | Version Published
Journal Article Open

Direct Imaging Explorations for Companions from the Subaru/IRD Strategic Program II; Discovery of a Brown-dwarf Companion around a Nearby Mid-M-dwarf LSPM J1446+4633

Creators

  • 1. ROR icon California State University, Northridge
  • 2. ROR icon National Astronomical Observatory of Japan
  • 3. ROR icon NASA Exoplanet Science Institute
  • 4. ROR icon Infrared Processing and Analysis Center
  • 5. ROR icon The Graduate University for Advanced Studies, SOKENDAI
  • 6. ROR icon Johns Hopkins University
  • 7. ROR icon Space Telescope Science Institute
  • 8. ROR icon Stockholm University
  • 9. ROR icon California Institute of Technology
  • 10. ROR icon Jet Propulsion Lab
  • 11. Department of Earth and Planetary Sciences, School of Science, Institute of Science Tokyo, 2-12-1 Ookayama, Meguro, Tokyo 152-8551, Japan
  • 12. ROR icon Sofia University
  • 13. ROR icon Ibaraki University
  • 14. ROR icon Max Planck Institute for Astronomy
  • 15. ROR icon Western University
  • 16. ROR icon University of Tokyo
  • 17. ROR icon Instituto de Astrofísica de Canarias
  • 18. ROR icon Shanghai Jiao Tong University
  • 19. ROR icon Niigata Institute of Technology
  • 20. ROR icon University of Hawaii at Hilo
  • 21. ROR icon Oita University
  • 22. ROR icon Tokyo University of Agriculture and Technology
  • 23. ROR icon National Astronomical Observatories
  • 24. East Asian Core Observatories Association fellow.

Abstract

We report the discovery of a new directly imaged brown-dwarf companion with Keck/NIRC2+pyWFS around a nearby mid-type M-dwarf LSPM J1446+4633 (hereafter J1446). The L'-band contrast (4.5 × 10−3) is consistent with a ∼20–60 MJup object at 1–10 Gyr and our two-epoch NIRC2 data suggest a ∼30% (∼3.1σ) variability in its L'-band flux. We incorporated Gaia DR3 non-single-star catalog into the orbital fitting by combining the Subaru/IRD radial velocity monitoring results, NIRC2 direct imaging (DI) results, and Gaia proper motion acceleration. As a result, we derive 59.8^(+1.5)_(-1.4) M_(Jup)  and ≈4.3 au for the dynamical mass and the semimajor axis of the companion J1446B, respectively. J1446B is one of the intriguing late-T dwarfs showing variability at L'-band for future atmospheric studies with the constrained dynamical mass. Because the J1446 system is accessible with various observation techniques such as astrometry, DI, and high-resolution spectroscopy including radial velocity measurement, it has a potential as a great benchmark system to improve our understanding for cool dwarfs.

Copyright and License

© 2025. 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.

Acknowledgement

The authors would like to thank the anonymous referee for their constructive comments and suggestions to improve the quality of the paper. We thank Guangyao Xiao for help in implementing fitting tool in F. Feng et al. (2023). M.K. and J.K. are supported by JSPS KAKENHI (grant No. 24K07108 for M.K. and 24K07086 for J.K). D.S. and T.T. acknowledge support by the BNSF program “VIHREN-2021” project No. KP-06-DV/5. The development and operation of IRD were supported by JSPS KAKENHI grant Nos. 18H05442, 15H02063, and 22000005, and Astrobilogy Center (ABC) of NINS. This work was supported in part by the NSF Graduate Research Fellowship (grant No. 2139433).

This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. The part of 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. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Data analysis was in part carried out on the Multi-wavelength Data Analysis System operated by the Astronomy Data Center (ADC), National Astronomical Observatory of Japan. This work has made use of data from the European Space Agency (ESA) mission Gaia (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. Funding for the TESS mission is provided by NASA’s Science Mission Directorate. We acknowledge the use of public TESS data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center (SPOC). Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. This paper includes data collected by the TESS mission that are publicly available from the Mikulski Archive for Space Telescopes (MAST). This research made use of Lightkurve, a Python package for Kepler and TESS data analysis (Lightkurve Collaboration et al. 2018). This publication makes use of VOSA, developed under the Spanish Virtual Observatory (https://svo.cab.inta-csic.es) project funded by MCIN/AEI/10.13039/501100011033/ through grant PID2020-112949GB-I00. This research has made use of NASA’s Astrophysics Data System Bibliographic Services. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.

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Additional details

Related works

Is new version of
Discussion Paper: arXiv:2509.13587 (arXiv)
Is supplemented by
Dataset: 10.17909/5zrm-fq94 (DOI)

Funding

Japan Society for the Promotion of Science
24K07108
Japan Society for the Promotion of Science
24K07086
Bulgarian National Science Fund
VIHREN-2021 No. KP-06-DV/5
Japan Society for the Promotion of Science
18H05442
Japan Society for the Promotion of Science
15H02063
Japan Society for the Promotion of Science
22000005
Astrobiology Center
NSF Graduate Research Fellowship
2139433
W. M. Keck Foundation

Dates

Accepted
2025-09-16
Available
2025-10-20
Published online

Caltech Custom Metadata

Caltech groups
Astronomy Department, Infrared Processing and Analysis Center (IPAC), Division of Physics, Mathematics and Astronomy (PMA)
Publication Status
Published