Weather on Other Worlds. VI. Optical Spectrophotometry of Luhman 16B Reveals Large-amplitude Variations in the Alkali Lines

Abstract

Using a novel wide-slit, multi-object approach with the GMOS spectrograph on the 8-meter Gemini South telescope, we have obtained precise time-series spectrophotometry of the binary brown dwarf Luhman 16 at optical wavelengths over two full nights. The B component of this binary system is known to be variable in the red optical and near-infrared with a period of 5 hr and an amplitude of 5--20%. Our observations probe its spectrally-resolved variability in the 6000--10000 Angstrom range. At wavelengths affected by the extremely strong, broadened spectral lines of the neutral alkali metals (the potassium doublet centered near 7682 Angstroms and the sodium doublet at 5893 Angstroms), we see photometric variations that differ strikingly from the those of the 8000--10000 Angstrom `red continuum' that dominates our detected flux. On UT 2014 February 24, these variations are anticorrelated with the red continuum, while on Feb 25 they have a large relative phase shift. The extent to which the wavelength-dependent photometric behavior diverges from that of the red continuum appears to correlate with the strength of the alkali absorption. We consider but ultimately reject models in which our observations are explained by lightning or auroral activity. A more likely cause is cloud-correlated, altitude-dependent variations in the gas-phase abundances of sodium and potassium, which are in chemical equilibrium with their chlorides in brown dwarf atmospheres. Clouds could influence these chemical equilibria by changing the atmospheric temperature profile and/or through cloud particles acting as chemical catalysts.

arXiv comment26 pages, 14 figures, accepted by ApJ

References in corpus (37)

• The VizieR database of Astronomical Catalogues
• Precipitating Condensation Clouds in Substellar Atmospheres
• Sixty-seven Additional L Dwarfs Discovered by the Two Micron All Sky Survey (2MASS)
• Weather on Other Worlds. II. Survey Results: Spots Are Ubiquitous on L and T Dwarfs
• Photometric Variability of the T2.5 Brown Dwarf SIMP J013656.5+093347; Evidence for Evolving Weather Patterns
• The Near-Infrared and Optical Spectra of Methane Dwarfs and Brown Dwarfs
• HST Spectral Mapping of L/T Transition Brown Dwarfs Reveals Cloud Thickness Variations
• Periodic Bursts of Coherent Radio Emission from an Ultracool Dwarf
• Large Amplitude Variations of an L/T Transition Brown Dwarf: Multi-Wavelength Observations of Patchy, High-Contrast Cloud Features
• A global cloud map of the nearest known brown dwarf
• Strong Brightness Variations Signal Cloudy-to-Clear Transition of Brown Dwarfs
• Discovery of a Binary Brown Dwarf at 2 Parsecs from the Sun
• The Spectra of T Dwarfs. II. Red Optical Data
• Vertical Atmospheric Structure in a Variable Brown Dwarf: Pressure-dependent Phase Shifts in Simultaneous Hubble Space Telescope-Spitzer Light Curves
• Clouds, Gravity and Metallicity in Blue L dwarfs: The Case of 2MASS J11263991-5003550
• Periodic Radio and H-alpha Emission from the L Dwarf Binary 2MASSW J0746425+200032: Exploring the Magnetic Field Topology and Radius of an L Dwarf
• Theoretical Spectral Models of T Dwarfs at Short Wavelengths and Their Comparison with Data
• 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
• Simultaneous, Multi-Wavelength Variability Characterization of the Free-Floating Planetary Mass Object PSO J318.5-22
• Cloud structure of the nearest brown dwarfs: Spectroscopic variability of Luhman 16AB from the Hubble Space Telescope
• Ionisation in atmospheres of Brown Dwarfs and extrasolar planets I The role of electron avalanche
• Characterization of the Nearby L/T Binary Brown Dwarf WISE J104915.57-531906.1 at 2 Parsecs from the Sun
• TESS Observations of the Luhman 16AB Brown Dwarf System: Rotational Periods, Lightcurve Evolution, and Zonal Circulation
• Ionisation in atmospheres of Brown Dwarfs and extrasolar planets II Dust-induced collisional ionization
• 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
• Neptune's Dynamic Atmosphere from Kepler K2 Observations: Implications for Brown Dwarf Light Curve Analyses
• Updated astrometry and masses of the LUH 16 brown dwarf binary
• Lightning climatology of exoplanets and brown dwarfs guided by Solar System data
• Rotational Light Curves of Jupiter from UV to Mid-Infrared and Implications for Brown Dwarfs and Exoplanets
• Weather on Other Worlds. III. A Survey for T Dwarfs with High Amplitude Optical Variability
• Hubble Space Telescope astrometry of the closest brown dwarf binary system -- I. Overview and improved orbit
• The Deepest Constraints on Radio and X-ray Magnetic Activity in Ultracool Dwarfs from WISE J104915.57-531906.1
• Characterizing The Cloud Decks of Luhman 16AB with Medium-Resolution Spectroscopic Monitoring
• Rotation periods and astrometric motions of the Luhman 16AB brown dwarfs by high-resolution lucky-imaging monitoring

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• 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