Cloud structure of the nearest brown dwarfs: Spectroscopic variability of Luhman 16AB from the Hubble Space Telescope

Abstract

The binary brown dwarf WISE J104915.57$-$531906.1 (also Luhman 16AB), composed of a late L and early T dwarf, is a prototypical L/T transition flux reversal binary located at only 2 pc distance. Luhman 16B is a known variable whose light curves evolve rapidly. We present spatially resolved spectroscopic time-series of Luhman 16A and B covering 6.5 h using HST/WFC3 at 1.1 to 1.66 $\mu$m. The small, count-dependent variability of Luhman 16A at the beginning of the observations likely stems from instrumental systematics; Luhman 16A appears non-variable above $\approx$0.4%. Its spectrum is well fit by a single cloud layer with intermediate cloud thickness (f_sed=2, Teff=1200 K). Luhman 16B varies at all wavelengths with peak-to-valley amplitudes of 7-11%. The amplitude and light curve shape changes over only one rotation period. The lowest relative amplitude is found in the deep water absorption band at 1.4 $\mu$m, otherwise it mostly decreases gradually from the blue to the red edge of the spectrum. This is very similar to the other two known highly variable early T dwarfs. A two-component cloud model accounts for most of the variability, although small deviations are seen in the water absorption band. We fit the mean spectrum and relative amplitudes with a linear combination of two models of a warm, thinner cloud (Teff=1300 K, fsed=3) and a cooler, thicker cloud (Teff=1000-1100 K, f_sed=1), assuming out-of-equilibrium atmospheric chemistry. A cloud as for Luhman 16A but with holes cannot reproduce the variability of Luhman 16B, indicating more complex cloud evolution through the L/T transition. The projected separation of the binary has decreased by $\approx$0.3'' in 8 months.

arXiv comment14 pages, 12 figures. Accepted for publication in ApJ

References in corpus (30)

• Precipitating Condensation Clouds in Substellar Atmospheres
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• The Hawaii Infrared Parallax Program. I. Ultracool Binaries and the L/T Transition
• Near-Infrared Photometry and Spectroscopy of L and T Dwarfs: the Effects of Temperature, Clouds, and Gravity
• L and T Dwarf Models and the L to T Transition
• The 0.8-14.5 micron Spectra of Mid-L to Mid-T Dwarfs: Diagnostics of Effective Temperature, Grain Sedimentation, Gas Transport, and Surface Gravity
• Atmospheric Parameters of Field 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
• A Patchy Cloud Model for the L to T Dwarf Transition
• 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
• Discovery of a Binary Brown Dwarf at 2 Parsecs from the Sun
• The Spectra of T Dwarfs. II. Red Optical Data
• Exoplanet Transit Spectroscopy Using WFC3: WASP-12 b, WASP-17 b, and WASP-19 b
• Vertical Atmospheric Structure in a Variable Brown Dwarf: Pressure-dependent Phase Shifts in Simultaneous Hubble Space Telescope-Spitzer Light Curves
• Brown Dwarf Photospheres are Patchy: A Hubble Space Telescope Near-infrared Spectroscopic Survey Finds Frequent Low-level Variability
• New H2 collision-induced absorption and NH3 opacity and the spectra of the coolest brown dwarfs
• Probing the extreme planetary atmosphere of WASP-12b
• Fast-evolving weather for the coolest of our two new substellar neighbours
• 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
• Spectral Variability from the Patchy Atmospheres of T and Y Dwarfs
• Signatures of Cloud, Temperature, and Gravity From Spectra of the Closest Brown Dwarfs
• Dust in the Photospheric Environment II. Effect on the Near Infrared Spectra of L and T Dwarfs
• A Monitoring Campaign for Luhman 16AB. I. Detection of Resolved Near-Infrared Spectroscopic Variability
• Characterization of the Nearby L/T Binary Brown Dwarf WISE J104915.57-531906.1 at 2 Parsecs from the Sun
• Possible astrometric discovery of a substellar companion to the closest binary brown dwarf system WISE J104915.57-531906.1

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