Characterizing The Cloud Decks of Luhman 16AB with Medium-Resolution Spectroscopic Monitoring

Abstract

We present results from a two-night R~4000 0.9-2.5 micron spectroscopic monitoring campaign of Luhman 16AB (L7.5 + T0.5). We assess the variability amplitude as a function of pressure level in the atmosphere of Luhman 16B: the more variable of the two components. The amplitude decreases monotonically with decreasing pressure, indicating that the source of variability - most likely patchy clouds - lies in the lower atmosphere. An unexpected result is that the strength of the K I absorption is higher in the faint state of Luhman 16B and lower in the bright state. We conclude that either the abundance of K I increases when the clouds roll in, potentially because of additional K I in the cloud itself, or that the temperature-pressure profile changes. We reproduce the change in K I absorption strengths with combinations of spectral templates to represent the bright and the faint variability states. These are dominated by a warmer L8 or L9 component, with a smaller contribution from a cooler T1 or T2 component. The success of this approach argues that the mechanism responsible for brown dwarf variability is also behind the diverse spectral morphology across the L-to-T transition. We further suggest that the L9-T1 part of the sequence represents a narrow but random ordering of effective temperatures and cloud fractions, obscured by the monotonic progression in methane absorption strength.

arXiv comment13 pages, 7 figures, ApJ in press

References in corpus (30)

• A Method of Correcting Near-Infrared Spectra for Telluric Absorption
• Precipitating Condensation Clouds in Substellar Atmospheres
• The Theory of Brown Dwarfs and Extrasolar Giant Planets
• An Infrared Spectroscopic Sequence of M, L and T Dwarfs
• Neglected Clouds in T and Y Dwarf Atmospheres
• The NIRSPEC Brown Dwarf Spectroscopic Survey. I. Low-Resolution Near-Infrared Spectra
• Weather on Other Worlds. II. Survey Results: Spots Are Ubiquitous on L and T Dwarfs
• Evidence for Cloud Disruption in the L/T Dwarf Transition
• Photometric Variability of the T2.5 Brown Dwarf SIMP J013656.5+093347; Evidence for Evolving Weather Patterns
• HST Spectral Mapping of L/T Transition Brown Dwarfs Reveals Cloud Thickness Variations
• Large Amplitude Variations of an L/T Transition Brown Dwarf: Multi-Wavelength Observations of Patchy, High-Contrast Cloud Features
• Strong Brightness Variations Signal Cloudy-to-Clear Transition of Brown Dwarfs
• A global cloud map of the nearest known brown dwarf
• Cloudless atmospheres for L/T dwarfs and extra-solar giant planets
• Discovery of a Binary Brown Dwarf at 2 Parsecs from the Sun
• Binaries and the L Dwarf/T Dwarf Transition
• MASE: A New Data--Reduction Pipeline for the Magellan Echellette Spectrograph
• Fast-evolving weather for the coolest of our two new substellar neighbours
• $ExtrasolarStorms$: Pressure-dependent Changes In Light Curve Phase In Brown Dwarfs From Simultaneous $Hubble$ and $Spitzer$ Observations
• Weather on the Nearest Brown Dwarfs: Resolved Simultaneous Multi-Wavelength Variability Monitoring of WISE J104915.57-531906.1AB
• Resolved Near-Infrared Spectroscopy of WISE J104915.57-531906.1AB: A Flux-Reversal Binary at the L dwarf/T dwarf Transition
• An independent analysis of the brown dwarf atmosphere monitoring (BAM) data: large-amplitude variability is rare outside the L/T transition
• Spectral Variability from the Patchy Atmospheres of T and Y Dwarfs
• Temperature Fluctuations as a Source of Brown Dwarf Variability
• Cloud structure of the nearest brown dwarfs: Spectroscopic variability of Luhman 16AB from the Hubble Space Telescope
• HST Rotational Spectral Mapping of Two L-Type Brown Dwarfs: Variability In and Out of Water Bands Indicates High-Altitude Haze Layers
• Signatures of Cloud, Temperature, and Gravity From Spectra of the Closest Brown Dwarfs
• A Monitoring Campaign for Luhman 16AB. I. Detection of Resolved Near-Infrared Spectroscopic Variability
• Maps of Evolving Cloud Structures in Luhman 16AB from HST Time-Resolved Spectroscopy
• Cloud Structure of the Nearest Brown Dwarfs II: High-amplitude variability for Luhman 16 A and B in and out of the 0.99 micron FeH feature

Cited by in corpus (11)

• Let the Great World Spin: Revealing the Stormy, Turbulent Nature of Young Giant Exoplanet Analogs with the Spitzer Space Telescope
• TESS Observations of the Luhman 16AB Brown Dwarf System: Rotational Periods, Lightcurve Evolution, and Zonal Circulation
• The JWST Weather Report from the Nearest Brown Dwarfs I: multi-period JWST NIRSpec + MIRI monitoring of the benchmark binary brown dwarf WISE 1049AB
• Cloud Atlas: Rotational Modulations in the L/T Transition Brown Dwarf Companion HN Peg B
• Rotational spectral modulation of cloudless atmospheres for L/T Brown Dwarfs and Extrasolar Giant Planets
• Revealing the Vertical Cloud Structure of a young low-mass Brown Dwarf, an analog to the beta-Pictoris b directly-imaged exoplanet, through Keck I/MOSFIRE spectro-photometric variability
• Detection of Na and K in the atmosphere of the hot Jupiter HAT-P-1b with P200/DBSP
• Long-term 4.6$\mu$m Variability in Brown Dwarfs and a New Technique for Identifying Brown Dwarf Binary Candidates
• Weather on Other Worlds. VI. Optical Spectrophotometry of Luhman 16B Reveals Large-amplitude Variations in the Alkali Lines
• Tracing the Top-of-the-atmosphere and Vertical Cloud Structure of a fast-rotating late T-dwarf
• A 1.48-2.48 $\mu$m R=28000 spectroscopic atlas of the L7.5 and T0.5 components of the nearest pair of brown dwarfs: Luhman 16AB