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

Taichi Uyama; Masayuki Kuzuhara; Charles Beichman; Teruyuki Hirano; Takayuki Kotani; Qier An; Timothy D. Brandt; Markus Janson; Dimitri Mawet; Mayuko Mori; Bun'Ei Sato; Denitza Stoeva; Motohide Tamura; Masataka Aizawa; Bryson Cale; Thomas Henning; Hiroyuki Tako Ishikawa; Norio Narita; Masahiro Ogihara; Aniket Sanghi; Trifon Trifonov; Jerry Xuan; Eiji Akiyama; Hiroki Harakawa; Klaus Hodapp; Masato Ishizuka; Shane Jacobson; Eiichiro Kokubo; Mihoko Konishi; Tomoyuki Kudo; Takashi Kurokawa; Jungmi Kwon; Jun Nishikawa; Masashi Omiya; Takuma Serizawa; Huan-Yu Teng; Akitoshi Ueda; Sebastien Vievard

arXiv · 2509.13587

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

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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 ($4.5\times10^{-3}$) is consistent with a $\sim20-60\ M_{\rm Jup}$ object at 1--10~Gyr and our two-epoch NIRC2 data suggest a $\sim30\%$ ($\sim3.1\sigma)$ variability in its $L'$-band flux. We incorporated Gaia DR3 non-single-star catalog into the orbital fitting by combining the Subaru/IRD RV monitoring results, NIRC2 direct imaging results, and Gaia proper motion acceleration. As a result, we derive ${59.8}_{-1.4}^{+1.5}\ M_{\rm Jup}$ and $\approx4.3~{\rm au}$ for the dynamical mass and the semi-major 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, direct imaging, and high-resolution spectroscopy including radial velocity measurement, it has a potential as a great benchmark system to improve our understanding for cool dwarfs.

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Taichi Uyama, Masayuki Kuzuhara, Charles Beichman, Teruyuki Hirano, Takayuki Kotani, Qier An, Timothy D. Brandt, Markus Janson, Dimitri Mawet, Mayuko Mori, Bun'Ei Sato, Denitza Stoeva, Motohide Tamura, Masataka Aizawa, Bryson Cale, Thomas Henning, Hiroyuki Tako Ishikawa, Norio Narita, Masahiro Ogihara, Aniket Sanghi, Trifon Trifonov, Jerry Xuan, Eiji Akiyama, Hiroki Harakawa, Klaus Hodapp, Masato Ishizuka, Shane Jacobson, Eiichiro Kokubo, Mihoko Konishi, Tomoyuki Kudo, Takashi Kurokawa, Jungmi Kwon, Jun Nishikawa, Masashi Omiya, Takuma Serizawa, Huan-Yu Teng, Akitoshi Ueda, Sebastien Vievard. 2025-09-16. 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. https://arxiv.org/abs/2509.13587

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