The ESO SupJup Survey VII: Clouds and line asymmetries in CRIRES${}^{+}$ J-band spectra of the Luhman 16 binary

Abstract

Brown dwarfs at the L-T transition likely experience an inhomogeneous clearing of the clouds in their atmospheres. The resulting surface of thin and thick cloudy patches has been put forward to explain the observed variability, J-band brightening, and re-emergence of FeH absorption. We study the closest brown dwarf binary, Luhman 16A and B, in an effort to constrain their chemical and cloud compositions. As this binary consists of an L7.5 and T0.5 component, we gain insight into the atmospheric properties at the L-T transition. As part of the ESO SupJup Survey, we observed Luhman 16AB at high spectral resolution in the J-band ($1.1-1.4\mu \mathrm{m}$) using CRIRES${}^{+}$. To analyse the spectra, we employ an atmospheric retrieval framework, coupling the radiative transfer code petitRADTRANS with the MultiNest sampling algorithm. For both objects, we report detections of H${}_2$O, K, Na, FeH, and, for the first time in the J-band, hydrogen-fluoride (HF). The K doublet at $1250\mathrm{nm}$ shows asymmetric absorption in the blue line wings, which are reproduced via pressure- and temperature-dependent shifts of the line cores. We find evidence for clouds in both spectra and we place constraints on an FeH-depletion in the Luhman 16A photosphere. The inferred over-abundance of FeH for Luhman 16B opposes its predicted rainout into iron clouds. A two-column model, which emulates the patchy surface expected at the L-T transition, is weakly preferred ($\sim 1.8\sigma$) for component B but disfavoured for A ($\sim 5.5\sigma$). The results suggest a uniform surface on Luhman 16A, which is in good agreement with the reduced variability observed for this L-type component. While the presented evidence is not sufficient to draw conclusions about any inhomogeneity on Luhman 16B, future observations covering a broader wavelength range could help to test the cloud-clearing hypothesis.

Accepted for publication in A&A

References in corpus (28)

• Array Programming with NumPy
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
• Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres
• Methane, Carbon Monoxide, and Ammonia in Brown Dwarfs and Self-Luminous Giant Planets
• Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e
• Detection of Fe I in the atmosphere of the ultra-hot Jupiter WASP-121b, and a new likelihood-based approach for Doppler-resolved spectroscopy
• Strong Brightness Variations Signal Cloudy-to-Clear Transition of Brown Dwarfs
• Water Clouds in Y Dwarfs and Exoplanets
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs I: Characterizing Benchmarks, Gl570D and HD3651B
• The NIRSPEC Brown Dwarf Spectroscopic Survey II: High-Resolution J-Band Spectra of M, L and T Dwarfs
• CRIRES${}^{+}$ on sky at the ESO Very Large Telescope
• Radial Velocity Measurements of HR 8799 b and c with Medium Resolution Spectroscopy
• Molecular Cross Sections for High Resolution Spectroscopy of Super Earths, Warm Neptunes and Hot Jupiters
• Cloud structure of the nearest brown dwarfs: Spectroscopic variability of Luhman 16AB from the Hubble Space Telescope
• Atmospheric circulation of brown dwarfs and directly imaged exoplanets driven by cloud radiative feedback: global and equatorial dynamics
• Signatures of Cloud, Temperature, and Gravity From Spectra of the Closest Brown Dwarfs
• The JWST Weather Report from the Nearest Brown Dwarfs I: multi-period JWST NIRSpec + MIRI monitoring of the benchmark binary brown dwarf WISE 1049AB
• Stellar parameters and H$\alpha$ line profile variability of Be stars in the BeSOS survey
• The ESO SupJup Survey III: Confirmation of 13CO in YSES 1 b and Atmospheric Detection of YSES 1 c with CRIRES+
• Individual, Model-Independent Masses of the Closest Known Brown Dwarf Binary to the Sun
• Hubble Space Telescope astrometry of the closest brown dwarf binary system -- I. Overview and improved orbit
• The ESO SupJup Survey II: The 12C/13C ratios of three young brown dwarfs with CRIRES${}^{+}$
• The ESO SupJup Survey IV. Unveiling the carbon isotope ratio of GQ Lup B and its host star
• Dynamically coupled kinetic chemistry in brown dwarf atmospheres I. Performing global scale kinetic modelling
• Global weather map reveals persistent top-of-atmosphere features on the nearest brown dwarfs