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A Monitoring Campaign for Luhman 16AB. I. Detection of Resolved Near-infrared Spectroscopic Variability

Burgasser, Adam J. and Gillon, Michaël and Faherty, Jacqueline K. and Radigan, Jacqueline and Triaud, Amaury H. M. J. and Plavchan, Peter and Street, Rachel and Jehin, E. and Delrez, L. and Opitom, C. (2014) A Monitoring Campaign for Luhman 16AB. I. Detection of Resolved Near-infrared Spectroscopic Variability. Astrophysical Journal, 785 (1). Art. No. 48. ISSN 0004-637X.

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We report resolved near-infrared spectroscopic monitoring of the nearby L dwarf/T dwarf binary WISE J104915.57–531906.1AB (Luhman 16AB), as part of a broader campaign to characterize the spectral energy distribution and temporal variability of this system. A continuous 45 minute sequence of low-resolution IRTF/SpeX data spanning 0.8-2.4 μm were obtained, concurrent with combined-light optical photometry with ESO/TRAPPIST. Our spectral observations confirm the flux reversal of this binary, and we detect a wavelength-dependent decline in the relative spectral fluxes of the two components coincident with a decline in the combined-light optical brightness of the system over the course of the observation. These data are successfully modeled as a combination of achromatic (brightness) and chromatic (color) variability in the T0.5 Luhman 16B, consistent with variations in overall cloud opacity; and no significant variability was found in L7.5 Luhman 16A, consistent with recent resolved photometric monitoring. We estimate a peak-to-peak amplitude of 13.5% at 1.25 μm over the full light curve. Using a simple two-spot brightness temperature model for Luhman 16B, we infer an average cold covering fraction of ≈30%-55%, varying by 15%-30% over a rotation period assuming a ≈200-400 K difference between hot and cold regions. We interpret these variations as changes in the covering fraction of a high cloud deck and corresponding "holes" which expose deeper, hotter cloud layers, although other physical interpretations are possible. A Rhines scale interpretation for the size of the variable features explains an apparent correlation between period and amplitude for Luhman 16B and the variable T dwarfs SIMP 0136+0933 and 2MASS J2139+0220, and predicts relatively fast winds (1-3 km s^(–1)) for Luhman 16B consistent with light curve evolution on an advective time scale (1-3 rotation periods). The strong variability observed in this flux reversal brown dwarf pair supports the model of a patchy disruption of the mineral cloud layer as a universal feature of the L dwarf/T dwarf transition.

Item Type:Article
Related URLs:
URLURL TypeDescription
Burgasser, Adam J.0000-0002-6523-9536
Gillon, Michaël0000-0003-1462-7739
Faherty, Jacqueline K.0000-0001-6251-0573
Radigan, Jacqueline0000-0002-6732-3651
Triaud, Amaury H. M. J.0000-0002-5510-8751
Plavchan, Peter0000-0002-8864-1667
Street, Rachel0000-0001-6279-0552
Delrez, L.0000-0001-6108-4808
Additional Information:© 2014 American Astronomical Society. Received 2013 December 17; accepted 2014 February 10; published 2014 March 25. The authors thank Michael Cushing for assistance in the SpeX component extraction; Dave Griep at IRTF for his assistance with the observations, and helpful comments and contributions from Daniel Apai. The authors also thank our anonymous referee for a helpful review. A.H.M.J. Triaud is a Swiss national science foundation fellow under grant PBGEP2-145594. TRAPPIST is a project funded by the Belgian Fund for Scientific Research (Fonds National de la Recherche Scientifique, F.R.SFNRS) under grant FRFC 2.5.594.09.F, with the participation of the Swiss National Science Foundation (SNF). M. Gillon and E. Jehin are FNRS Research Associates. This research has benefitted from the SpeX Prism Spectral Libraries, maintained by Adam Burgasser at; and the M, L, T, and Y dwarf compendium housed at The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facility: IRTF (SpeX)
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Swiss National Science Foundation (SNSF)PBGEP2-145594
Fonds National de la Recherche Scientifique (FNRS)FRFC 2.5.594.09.F
Subject Keywords:binaries: visual; brown dwarfs; stars: individual (WISE J104915.57-531906.1AB, Luhman 16AB); stars: low-mass
Issue or Number:1
Record Number:CaltechAUTHORS:20140609-092424134
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Official Citation:A Monitoring Campaign for Luhman 16AB. I. Detection of Resolved Near-infrared Spectroscopic Variability Adam J. Burgasser et al. 2014 ApJ 785 48
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46143
Deposited By: Ruth Sustaita
Deposited On:09 Jun 2014 16:50
Last Modified:09 Mar 2020 13:19

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