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Title: Cloud structure of the nearest brown dwarfs. II: High-amplitude variability for Luhman 16 A and B in and out of the 0.99 μm FeH feature

The re-emergence of the 0.99 μm FeH feature in brown dwarfs of early- to mid-T spectral type has been suggested as evidence for cloud disruption where flux from deep, hot regions below the Fe cloud deck can emerge. The same mechanism could account for color changes at the L/T transition and photometric variability. We present the first observations of spectroscopic variability of brown dwarfs covering the 0.99 μm FeH feature. We observed the spatially resolved very nearby brown dwarf binary WISE J104915.57–531906.1 (Luhman 16AB), a late-L and early-T dwarf, with Hubble Space Telescope/WFC3 in the G102 grism at 0.8–1.15 μm. We find significant variability at all wavelengths for both brown dwarfs, with peak-to-valley amplitudes of 9.3% for Luhman 16B and 4.5% for Luhman 16A. This represents the first unambiguous detection of variability in Luhman 16A. We estimate a rotational period between 4.5 and 5.5 hr, very similar to Luhman 16B. Variability in both components complicates the interpretation of spatially unresolved observations. The probability for finding large amplitude variability in any two brown dwarfs is less than 10%. Our finding may suggest that a common but yet unknown feature of the binary is important for the occurrence of variability. For bothmore » objects, the amplitude is nearly constant at all wavelengths except in the deep K i feature below 0.84 μm. No variations are seen across the 0.99 μm FeH feature. The observations lend strong further support to cloud height variations rather than holes in the silicate clouds, but cannot fully rule out holes in the iron clouds. Here, we re-evaluate the diagnostic potential of the FeH feature as a tracer of cloud patchiness.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [3] ;  [6]
  1. Max Plank Institute for Astronomy, Heidelberg (Germany)
  2. NASA Ames Reseach Center, Moffett Field, CA (United States)
  3. Univ. of Arizona, Tucson, AZ (United States)
  4. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  5. Univ. of Edinburgh, Edinburgh (United Kingdom)
  6. Space Telescope Science Institute, Baltimore, MD (United States)
Publication Date:
OSTI Identifier:
1296663
Report Number(s):
LA-UR--15-24263
Journal ID: ISSN 1538-4357
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 812; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
NASA; USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS binaries: visual; brown dwarfs; stars: atmospheres; stars: individual (WISE J104915.57-531906.1Luhman 16AB); stars: variables: general