Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cloud Atlas: Variability in and out of the Water Band in the
  Planetary-mass HD 203030B Points to Cloud Sedimentation in Low-gravity L
  Dwarfs   We use the Wide Field Camera 3 on the {\sl Hubble Space Telescope} to
spectrophotometrically monitor the young L7.5 companion HD~203030B. Our time
series reveal photometric variability at 1.27\,$\mu$m and 1.39\,$\mu$m on time
scales compatible with rotation. We find a rotation period of
$7.5^{+0.6}_{-0.5}$ h: comparable to those observed in other brown dwarfs and
planetary-mass companions younger than 300 Myr. We measure variability
amplitudes of $1.1\pm0.3\%$ (1.27\,$\mu$m) and $1.7\pm0.4\%$ (1.39\,$\mu$m),
and a phase lag of 56$^\circ\pm$28$^\circ$ between the two light curves. We
attribute the difference in photometric amplitudes and phases to a patchy cloud
layer that is sinking below the level where water vapor becomes opaque. HD
203030B and the few other known variable young late-L dwarfs are unlike warmer
(earlier-type and/or older) L dwarfs, for which variability is much less
wavelength-dependent across the 1.1--1.7$\mu$m region. We further suggest that
a sinking of the top-most cloud deck below the level where water or carbon
monoxide gas become opaque may also explain the often enhanced variability
amplitudes of even earlier-type low-gravity L dwarfs. Because these condensate
and gas opacity levels are already well-differentiated in T dwarfs, we do not
expect the same variability amplitude enhancement in young vs.\ old T dwarfs.

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The categories of this paper are: atom-ph
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The categories of this paper are: solv-int
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The categories of this paper are: supr-con
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The categories of this paper are: hep-ex
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The categories of this paper are: adap-org
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The categories of this paper are: econ
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The categories of this paper are: eess
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The categories of this paper are: cond-mat
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The categories of this paper are: stat
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The categories of this paper are: acc-phys
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The categories of this paper are: nlin
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The categories of this paper are: hep-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-lat
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The categories of this paper are: q-alg
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The categories of this paper are: chem-ph