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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

Journal Article · · The Astrophysical Journal (Online)
 [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)
+ Show Author Affiliations

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 both 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.

Research Organization:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
NASA; USDOE
Grant/Contract Number:
AC52-06NA25396
OSTI ID:
1296663
Alternate ID(s):
OSTI ID: 22518742
Report Number(s):
LA-UR--15-24263
Journal Information:
The Astrophysical Journal (Online), Journal Name: The Astrophysical Journal (Online) Journal Issue: 2 Vol. 812; ISSN 1538-4357
Publisher:
Institute of Physics (IOP)Copyright Statement
Country of Publication:
United States
Language:
English

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Cited By (10)

Dust in brown dwarfs and extra-solar planets: II. Cloud formation for cosmologically evolving abundances journal September 2009
Characterization of exoplanets from their formation: III. The statistics of planetary luminosities journal December 2017
Detection of new strongly variable brown dwarfs in the L/T transition journal September 2019
Dust in brown dwarfs and extra-solar planets: VII. Cloud formation in diffusive atmospheres journal January 2020
Dust in brown dwarfs and extra-solar planets: I. Chemical composition and spectral appearance of quasi-static cloud layers journal April 2008
Simultaneous Multiwavelength Variability Characterization of the Free-floating Planetary-mass Object PSO J318.5−22 journal January 2018
Spitzer Light Curves of the Young, Planetary-mass TW Hya Members 2MASS J11193254–1137466AB and WISEA J114724.10–204021.3 journal May 2018
The Viewing Geometry of Brown Dwarfs Influences Their Observed Colors and Variability Amplitudes journal June 2017
Atmospheric Variability Driven by Radiative Cloud Feedback in Brown Dwarfs and Directly Imaged Extrasolar Giant Planets journal March 2019
Spitzer Light Curves of the Young, Planetary-Mass TW Hya Members 2MASS J11193254-1137466AB and WISEA J114724.10-204021.3 text January 2018

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Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
binaries: visual
brown dwarfs
stars: atmospheres
stars: individual (WISE J104915.57-531906.1Luhman 16AB)
stars: variables: general