Signatures of Cloud, Temperature, and Gravity From Spectra of the Closest Brown Dwarfs

Abstract

We present medium resolution optical and NIR spectral data for components of the newly discovered WISE J104915.57-531906.1AB (Luhman 16AB) brown dwarf binary. The optical spectra reveal strong 6708 A Li I absorption in both Luhman 16A (8.0+/-0.4 A) and Luhman 16B (3.8+/-0.4 A). Interestingly, this is the first detection of Li I absorption in a T dwarf. Combined with the lack of surface gravity features, the Li I detection constrains the system age to 0.1 - 3 Gyr. In the NIR data, we find strong KI absorption at 1.168, 1.177, 1.243, and 1.254 μm in both components. Compared to the strength of KI line absorption in equivalent spectral subtype brown dwarfs, Luhman 16A is weaker while Luhman 16B is stronger. Analyzing the spectral region around each doublet in distance scaled flux units and comparing the two sources, we confirm the J band flux reversal and find that Luhman 16B has a brighter continuum in the 1.17 μm and 1.25 μm regions than Luhman 16A. Converting flux units to a brightness temperature we interpret this to mean that the secondary is ~ 50 K warmer than the primary in regions dominated by condensate grain scattering. One plausible explanation for this difference is that Luhman 16B has thinner clouds or patchy holes in its atmosphere allowing us to see to deeper, hotter regions. We also detect comparably strong FeH in the 0.9896 μm Wing-Ford band for both components. Traditionally, a signpost of changing atmosphere conditions from late-type L to early T dwarfs, the persistence and similarity of FeH at 0.9896 μm in both Luhman 16A and Luhman 16B is an indication of homogenous atmosphere conditions. We calculate bolometric luminosities from observed data supplemented with best fit models for longer wavelengths and find the components are consistent within 1σ with resultant Teffs of 1310+/-30 K and 1280+/-75 K for Luhman 16AB respectively.

17 pages, 11 figures, 4 tables. Submitted to ApJ and revised after referee report

References in corpus (13)

• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• 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
• Young L Dwarfs Identified in the Field: A Preliminary Low-Gravity, Optical Spectral Sequence from L0 to L5
• Meeting the Cool Neighbors. IX. The Luminosity Function of M7-L8 Ultracool Dwarfs in the Field
• A Sample of Very Young Field L Dwarfs and Implications for the Brown Dwarf "Lithium Test" at Early Ages
• Characterizing Young Brown Dwarfs using Low Resolution Near-IR Spectra
• Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition
• The MagE Spectrograph
• Discovery of Two Nearby, Peculiar L Dwarfs from the 2MASS Proper Motion Survey: Young or Metal-Rich?
• Vertical Atmospheric Structure in a Variable Brown Dwarf: Pressure-dependent Phase Shifts in Simultaneous Hubble Space Telescope-Spitzer Light Curves
• The NIRSPEC Brown Dwarf Spectroscopic Survey II: High-Resolution J-Band Spectra of M, L and T Dwarfs
• The Brown dwarf Atmosphere Monitoring (BAM) Project I: The largest near-IR monitoring survey of L- & T-dwarfs
• Dynamical masses for the nearest brown dwarf binary: Epsilon Indi Ba, Bb

Cited by in corpus (34)

• The Field Substellar Mass Function Based on the Full-sky 20-pc Census of 525 L, T, and Y Dwarfs
• Balancing the Energy Budget of Short-Period Giant Planets: Evidence for Reflective Clouds and Optical Absorbers
• Aerosols in Exoplanet Atmospheres
• Cloud structure of the nearest brown dwarfs: Spectroscopic variability of Luhman 16AB from the Hubble Space Telescope
• In-depth study of moderately young but extremely red, very dusty substellar companion HD206893B
• A New Sedimentation Model for Greater Cloud Diversity in Giant Exoplanets and Brown Dwarfs
• The Mass-Luminosity Relation in the L/T Transition: Individual Dynamical Masses for the New J-Band Flux Reversal Binary SDSSJ105213.51+442255.7AB
• COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-Gravity T4 Benchmark around an Old White Dwarf and A Re-Examination of the Surface-Gravity Dependence of the L/T Transition
• The JWST Weather Report from the Nearest Brown Dwarfs I: multi-period JWST NIRSpec + MIRI monitoring of the benchmark binary brown dwarf WISE 1049AB
• Methane Emission From a Cool Brown Dwarf
• Lightning climatology of exoplanets and brown dwarfs guided by Solar System data
• Rotational spectral modulation of cloudless atmospheres for L/T Brown Dwarfs and Extrasolar Giant Planets
• Characterizing the Cool KOIs. VII. Refined Physical Properties of the Transiting Brown Dwarf LHS 6343 C
• 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
• Temperature constraints on the coldest brown dwarf known WISE 0855-0714
• Physical properties and trigonometric distance of the peculiar dwarf WISE J181005.5$-$101002.3
• The Oceanus Moving Group: A New 500 Myr-Old Host for the Nearest Brown Dwarf
• A new L5 brown dwarf member of the Hyades cluster with chromospheric activity
• The Deepest Constraints on Radio and X-ray Magnetic Activity in Ultracool Dwarfs from WISE J104915.57-531906.1
• Combining Gaia and GRAVITY: Characterising five new Directly Detected Substellar Companions
• Characterization of the known T type dwarfs towards the Sigma Orionis cluster
• A search for lithium in metal-poor L dwarfs
• Global weather map reveals persistent top-of-atmosphere features on the nearest brown dwarfs
• Characterizing The Cloud Decks of Luhman 16AB with Medium-Resolution Spectroscopic Monitoring
• The ESO SupJup Survey VII: Clouds and line asymmetries in CRIRES${}^{+}$ J-band spectra of the Luhman 16 binary
• HST astrometry of the closest Brown Dwarfs -- II. Improved parameters and constraints on a third body
• Search for the sub-stellar lithium depletion boundary in the open star cluster Coma Berenices
• One of Everything: The Breakthrough Listen Exotica Catalog
• Diversity of Cold Worlds: A Near Complete Spectral Energy Distribution for 2MASS J04151954-0935066 using JWST
• 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
• Patchy nightside clouds on ultra-hot Jupiters: General Circulation Model simulations with radiatively active cloud tracers
• New constraints on the minimum mass for thermonuclear lithium burning in brown dwarfs
• Disentangling the Signatures of Blended-Light Atmospheres in L/T Transition Brown Dwarfs