Atmospheric retrieval of Subaru/IRD high-resolution spectrum of the archetype T-type brown dwarf Gl 229 B

Abstract

Brown dwarfs provide a unique opportunity to study atmospheres and their physical and chemical processes with high precision, especially in temperature ranges relevant to exoplanets. In this study, we performed high-resolution ($R\sim 70,000$) spectroscopy using Subaru/IRD ($Y$, $J$, $H$-bands) of the T7.0p-type object Gl 229 B, the first discovered T-type brown dwarf, which orbits an M1V host star at a separation of 33 au. We conducted atmospheric retrieval on the reduced $H$-band spectrum using the high-resolution spectrum model compatible with automatic differentiation and GPU, ExoJAX. In contrast to previous retrieval studies on medium-resolution spectra, we obtained a C/O ratio consistent with that of the host star, aligning with the expected formation process for such a massive brown dwarf. Additionally, based on the strong constraint on temperature from the high-resolution spectrum and previously measured photometric magnitude, our analysis indicates that Gl 229 B is a binary, which was also proposed by Brandt et al. (2021) and recently confirmed by Xuan et al. (2024). Finally, we validated current molecular line lists by leveraging the obtained high-resolution, high signal-to-noise ratio spectrum of this warm ($\sim 900$ K) atmosphere. This study highlights the importance of observing companion brown dwarfs as benchmark objects for establishing characterization techniques for low-mass objects and enhancing our understanding of their atmospheres, given the wealth of available information and the relative ease of observation.

arXiv comment20 pages, 11 figures, accepted for publication in ApJ

References in corpus (45)

• Array Programming with NumPy
• Astropy: A Community Python Package for Astronomy
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• The effects of snowlines on C/O in planetary atmospheres
• The orbital motion, absolute mass, and high-altitude winds of exoplanet HD209458b
• The chemical make-up of the Sun: A 2020 vision
• ExoMol molecular line lists XXX: a complete high-accuracy line list for water
• The ExoMol database: molecular line lists for exoplanet and other hot atmospheres
• A Unified Near Infrared Spectral Classification Scheme for T Dwarfs
• The Brown Dwarf Kinematics Project (BDKP). III. Parallaxes for 70 Ultracool Dwarfs
• ExoMol molecular line lists XXXV: a rotation-vibration line list for hot ammonia
• An accurate, extensive, and practical line list of methane for the HITEMP database
• Methane, Carbon Monoxide, and Ammonia in Brown Dwarfs and Self-Luminous Giant Planets
• A global cloud map of the nearest known brown dwarf
• A hybrid line list for CH${}_4$ and hot methane continuum
• High-Resolution Spectroscopic Detection of TiO and Stratosphere in the Day-side of WASP-33b
• Molecular Abundances in the Atmosphere of the T Dwarf Gl 229B
• FastChem: A computer program for efficient complex chemical equilibrium calculations in the neutral/ionized gas phase with applications to stellar and planetary atmospheres
• The Spectrum of the Brown Dwarf Gliese 229B
• Constraining High Speed Winds in Exoplanet Atmospheres Through Observations of Anomalous Doppler Shifts During Transit
• Aerosols in Exoplanet Atmospheres
• The Near-infrared Spectrum of the Brown Dwarf Gliese 229B
• Physical Properties of Young Brown Dwarfs and Very Low-Mass Stars Inferred from High-Resolution Model Spectra
• The NIRSPEC Brown Dwarf Spectroscopic Survey II: High-Resolution J-Band Spectra of M, L and T Dwarfs
• Revised Fluxes for Gliese 229B
• Improved Dynamical Masses for Six Brown Dwarf Companions Using Hipparcos and Gaia EDR3
• First Detection of Hydroxyl Radical Emission from an Exoplanet Atmosphere: High-dispersion Characterization of WASP-33b using Subaru/IRD
• Precision radial velocity measurements by the forward-modeling technique in the near-infrared
• A Dynamical Mass of $70\pm 5$ Jupiter Masses for Gliese 229B, the First T Dwarf
• Neighbours hiding in the Galactic plane - a new M/L dwarf candidate for the 8pc sample
• Implementation of disequilibrium chemistry to spectral retrieval code ARCiS and application to sixteen exoplanet transmission spectra: Indication of disequilibrium chemistry for HD 209458b and WASP-39b
• Retrieving the C and O Abundances of HR 7672~AB: a Solar-Type Primary Star with a Benchmark Brown Dwarf
• A high resolution spectral atlas of brown dwarfs
• Elemental Abundances of M Dwarfs Based on High-Resolution Near-Infrared Spectra: Verification by Binary Systems
• A 1.46-2.48 $\mu$m Spectroscopic Atlas of a T6 Dwarf (1060 K) Atmosphere with IGRINS: First Detections of H${}_2$S and H${}_2$, and Verification of H${}_2$O, CH${}_4$, and NH${}_3$ Line Lists
• An Atmospheric Retrieval of the Brown Dwarf Gliese 229B
• Auto-Differentiable Spectrum Model for High-Dispersion Characterization of Exoplanets and Brown Dwarfs
• Elemental abundances of nearby M dwarfs based on high-resolution near-infrared spectra obtained by the Subaru/IRD survey: Proof of concept
• The cool brown dwarf Gliese 229 B is a close binary
• High-Resolution Infrared Spectroscopy of the Brown Dwarf Epsilon Indi Ba
• Neutral metals in the atmosphere of HD149026b
• TOI-1696: a nearby M4 dwarf with a $3R_{\oplus }$ planet in the Neptunian desert
• Physical Properties of Gliese 229B Based on Newly Determined Carbon and Oxygen Abundances of Gliese 229A
• Discovery of the Binarity of Gliese 229B, and Constraints on the System's Properties

Cited by in corpus (1)

• PyIRD: A Python-Based Data Reduction Pipeline for Subaru/IRD and REACH