A Caltech Library Service

COol Companions ON Ultrawide orbiTS (COCONUTS). III. A Very Red L6 Benchmark Brown Dwarf around a Young M5 Dwarf

Zhang, Zhoujian and Liu, Michael C. and Morley, Caroline V. and Magnier, Eugene A. and Tucker, Michael A. and Vanderbosch, Zachary P. and Do, Aaron and Shappee, Benjamin J. (2022) COol Companions ON Ultrawide orbiTS (COCONUTS). III. A Very Red L6 Benchmark Brown Dwarf around a Young M5 Dwarf. Astrophysical Journal, 935 (1). Art. No. 15. ISSN 0004-637X. doi:10.3847/1538-4357/ac7ce9.

[img] PDF - Published Version
Creative Commons Attribution.

[img] PDF - Accepted Version
See Usage Policy.


Use this Persistent URL to link to this item:


We present the third discovery from the COol Companions ON Ultrawide orbiTS (COCONUTS) program, the COCONUTS-3 system, composed of the young M5 primary star UCAC4 374−046899 and the very red L6 dwarf WISEA J081322.19−152203.2. These two objects have a projected separation of 61" (1891 au) and are physically associated given their common proper motions and estimated distances. The primary star, COCONUTS-3A, has a mass of 0.123 ± 0.006 M_⊙, and we estimate its age as 100 Myr to 1 Gyr based on its stellar activity (via Hα and X-ray emission), kinematics, and spectrophotometric properties. We derive its bulk metallicity as 0.21 ± 0.07 dex using empirical calibrations established by older and higher-gravity M dwarfs and find that this [Fe/H] could be slightly underestimated according to PHOENIX models given COCONUTS-3A’s younger age. The companion, COCONUTS-3B, has a near-infrared spectral type of L6 ± 1 int-g, and we infer physical properties of T_(eff) = 1362₋₇₃⁺⁴⁸ K, log(g) = 4.96_(-0.34)^(+0.15) dex, R = 1.03_(-0.06)^(+0.12) R_(Jup), and M = 39₋₁₈⁺¹¹ M_(Jup) using its bolometric luminosity, its host star’s age, and hot-start evolution models. We construct cloudy atmospheric model spectra at the evolution-based physical parameters and compare them to COCONUTS-3B’s spectrophotometry. We find that this companion possesses ample condensate clouds in its photosphere (f_(sed) = 1) with the data–model discrepancies likely due to the models using an older version of the opacity database. Compared to field-age L6 dwarfs, COCONUTS-3B has fainter absolute magnitudes and a 120 K cooler T_(eff). Also, the J − K color of this companion is among the reddest for ultracool benchmarks with ages older than a few hundred megayears. COCONUTS-3 likely formed in the same fashion as stellar binaries given the companion-to-host mass ratio of 0.3 and represents a valuable benchmark to quantify the systematics of substellar model atmospheres.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Zhang, Zhoujian0000-0002-3726-4881
Liu, Michael C.0000-0003-2232-7664
Morley, Caroline V.0000-0002-4404-0456
Magnier, Eugene A.0000-0002-7965-2815
Tucker, Michael A.0000-0002-2471-8442
Vanderbosch, Zachary P.0000-0002-0853-3464
Do, Aaron0000-0003-3429-7845
Shappee, Benjamin J.0000-0003-4631-1149
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 2021 November 2; revised 2022 June 25; accepted 2022 June 27; published 2022 August 9. Z.Z. thanks Didier Saumon for sharing the Saumon & Marley (2008) atmospheric model spectra, Andre-Nicolas Chene and Bin Yang for helpful discussions about the Gemini/GMOS data reduction, Eric Mamajek for discussions about the typical photometric properties of dwarf stars, Andrew Mann for discussions about the empirical metallicity calibrations of young low-mass stars, Eunkyu Han for discussions about the magnetic fields in M dwarfs, and Adam Kraus and Brendan Bowler for helpful comments on the manuscript. Z.P.V. acknowledges the Heising-Simons Foundation for postdoctoral scholar support at Caltech. This work has benefited from The UltracoolSheet at, 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 Ultracool RIZzo Spectral Library (, maintained by Jonathan Gagné and Kelle Cruz. This research has benefited from the Montreal Brown Dwarf and Exoplanet Spectral Library, maintained by Jonathan Gagné. This work is based in part on observations obtained at the international Gemini Observatory, a program of NSF's NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). This research has made use of the NASA/IPAC Infrared Science Archive, which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC; Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Facilities: UH 2.2m (SNIFS), Gemini (GMOS, GNIRS), IRTF (SpeX). Software: emcee (Foreman-Mackey et al. 2013), BANYAN Σ (version 1.2; Gagné et al. 2018), LACEwING (Riedel et al. 2017), TOPCAT (Taylor 2005), Astropy (Astropy Collaboration et al. 2013, 2018), IPython (Pérez & Granger 2007), Numpy (Oliphant 2006), Scipy (Jones et al. 2001), Matplotlib (Hunter 2007).
Funding AgencyGrant Number
Heising-Simons FoundationUNSPECIFIED
Gemini PartnershipUNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:Brown dwarfs; L dwarfs; Substellar companion stars; M stars
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Brown dwarfs (1389); L dwarfs (894); Substellar companion stars (1648); M stars (985)
Record Number:CaltechAUTHORS:20220810-402655000
Persistent URL:
Official Citation:Zhoujian Zhang et al 2022 ApJ 935 15
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:116224
Deposited By: George Porter
Deposited On:12 Aug 2022 02:04
Last Modified:12 Aug 2022 02:04

Repository Staff Only: item control page