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A Clear View of a Cloudy Brown Dwarf Companion from High-resolution Spectroscopy

Xuan, Jerry W. and Wang, Jason and Ruffio, Jean-Baptiste and Knutson, Heather A. and Mawet, Dimitri and Mollière, Paul and Kolecki, Jared and Vigan, Arthur and Mukherjee, Sagnick and Wallack, Nicole and Wang, Ji and Baker, Ashley and Bartos, Randall and Blake, Geoffrey A. and Bond, Charlotte Z. and Bryan, Marta and Calvin, Benjamin and Cetre, Sylvain and Chun, Mark and Delorme, Jacques-Robert and Doppmann, Greg and Echeverri, Daniel and Finnerty, Luke and Fitzgerald, Michael P. and Horstman, Katelyn and Inglis, Julie and Jovanovic, Nemanja and López, Ronald and Martin, Emily C. and Morris, Evan and Pezzato, Jacklyn and Ragland, Sam and Ren, Bin and Ruane, Garreth and Sappey, Ben and Schofield, Tobias and Skemer, Andrew and Venenciano, Taylor and Wallace, J. Kent and Wizinowich, Peter (2022) A Clear View of a Cloudy Brown Dwarf Companion from High-resolution Spectroscopy. Astrophysical Journal, 937 (2). 54Art. No.. ISSN 0004-637X. doi:10.3847/1538-4357/ac8673.

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Direct imaging studies have mainly used low-resolution spectroscopy (R ∼ 20–100) to study the atmospheres of giant exoplanets and brown dwarf companions, but the presence of clouds has often led to degeneracies in the retrieved atmospheric abundances (e.g., carbon-to-oxygen ratio, metallicity). This precludes clear insights into the formation mechanisms of these companions. The Keck Planet Imager and Characterizer (KPIC) uses adaptive optics and single-mode fibers to transport light into NIRSPEC (R ∼ 35,000 in the K band), and aims to address these challenges with high-resolution spectroscopy. Using an atmospheric retrieval framework based on petitRADTRANS, we analyze the KPIC high-resolution spectrum (2.29–2.49 μm) and the archival low-resolution spectrum (1–2.2 μm) of the benchmark brown dwarf HD 4747 B (m = 67.2 ± 1.8 M_(Jup), a = 10.0 ± 0.2 au, T_(eff) ≈ 1400 K). We find that our measured C/O and metallicity for the companion from the KPIC high-resolution spectrum agree with those of its host star within 1σ–2σ. The retrieved parameters from the K-band high-resolution spectrum are also independent of our choice of cloud model. In contrast, the retrieved parameters from the low-resolution spectrum are highly sensitive to our chosen cloud model. Finally, we detect CO, H₂O, and CH₄ (volume-mixing ratio of log(CH₄) = −4.82 ± 0.23) in this L/T transition companion with the KPIC data. The relative molecular abundances allow us to constrain the degree of chemical disequilibrium in the atmosphere of HD 4747 B, and infer a vertical diffusion coefficient that is at the upper limit predicted from mixing length theory.

Item Type:Article
Related URLs:
URLURL TypeDescription
Xuan, Jerry W.0000-0002-6618-1137
Wang, Jason0000-0003-0774-6502
Ruffio, Jean-Baptiste0000-0003-2233-4821
Knutson, Heather A.0000-0002-5375-4725
Mawet, Dimitri0000-0002-8895-4735
Mollière, Paul0000-0003-4096-7067
Kolecki, Jared0000-0002-6267-0849
Vigan, Arthur0000-0002-5902-7828
Wallack, Nicole0000-0003-0354-0187
Wang, Ji0000-0002-4361-8885
Baker, Ashley0000-0002-6525-7013
Blake, Geoffrey A.0000-0003-0787-1610
Bryan, Marta0000-0002-6076-5967
Calvin, Benjamin0000-0003-4737-5486
Chun, Mark0000-0002-8462-0703
Delorme, Jacques-Robert0000-0001-8953-1008
Echeverri, Daniel0000-0002-1583-2040
Finnerty, Luke0000-0002-1392-0768
Fitzgerald, Michael P.0000-0002-0176-8973
Horstman, Katelyn0000-0001-9708-8667
Jovanovic, Nemanja0000-0001-5213-6207
Martin, Emily C.0000-0002-0618-5128
Pezzato, Jacklyn0000-0002-6769-2035
Ren, Bin0000-0003-1698-9696
Ruane, Garreth0000-0003-4769-1665
Skemer, Andrew0000-0001-6098-3924
Wallace, J. Kent0000-0001-5299-6899
Wizinowich, Peter0000-0002-1646-442X
Additional Information:We 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. This research has benefitted from the SpeX Prism Library maintained by Adam Burgasser at Funding for KPIC has been provided by the California Institute of Technology, the Jet Propulsion Laboratory, the Heising-Simons Foundation, the Simons Foundation, and the United States National Science Foundation grant No. AST-1611623. A.V. acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program, grant agreement Nos. 757561 (HiRISE). H.A.K. acknowledges support from the President's and Director's Research & Development Fund Program, which is jointly funded by the Jet Propulsion Laboratory and the California Institute of Technology under a contract with the National Aeronautics and Space Administration. The computations presented here were conducted in the Resnick High Performance Center, a facility supported by Resnick Sustainability Institute at the California Institute of Technology.
Group:Astronomy Department, Resnick Sustainability Institute
Funding AgencyGrant Number
Simons FoundationUNSPECIFIED
European Research Council (ERC)757561
JPL President and Director's FundUNSPECIFIED
Resnick Sustainability InstituteUNSPECIFIED
Issue or Number:2
Record Number:CaltechAUTHORS:20221010-454096500.18
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:117302
Deposited By: Research Services Depository
Deposited On:14 Oct 2022 18:00
Last Modified:14 Oct 2022 18:00

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