Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hot spots and a clumpy disk: Variability of brown dwarfs and stars in
  the young Sigma Ori cluster   The properties of accretion disks around stars and brown dwarfs in the SOri
cluster (age 3 Myr) are studied based on NIR time series photometry supported
by MIR spectral energy distributions. We monitor ~30 young low-mass sources
over 8 nights in the J- and K-band using the duPont telescope at Las Campanas.
We find three objects showing variability with J-band amplitudes >0.5 mag; five
additional objects exhibit low-level variations. All three highly variable
sources have been previously identified as highly variable; thus we establish
the long-term nature of their flux changes. The lightcurves contain periodic
components with timescales of ~0.5-8 days, but have additional irregular
variations superimposed -- the characteristic behaviour for classical T Tauri
stars. Based on the colour variability, we conclude that hot spots are the
dominant cause of the variations in two objects, including one likely brown
dwarf, with spot temperatures in the range of 6000-7000 K. For the third one
(#2), a brown dwarf or very low mass star, inhomogenities at the inner edge of
the disk are the likely origin of the variability. Based on mid-infrared data
from Spitzer, we confirm that the three highly variable sources are surrounded
by circum-(sub)-stellar disks. They show typical SEDs for T Tauri-like objects.
Using SED models we infer an enhanced scaleheight in the disk for the object
#2, which favours the detection of disk inhomogenities in lightcurves and is
thus consistent with the information from variability. In the SOri cluster,
about every fifth accreting low-mass object shows persistent high-level
photometric variability. We demonstrate that estimates for fundamental
parameters in such objects can be significantly improved by determining the
extent and origin of the variations.

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The categories of this paper are: hep-th
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The categories of this paper are: nlin
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The categories of this paper are: mtrl-th
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The categories of this paper are: stat
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The categories of this paper are: adap-org
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The categories of this paper are: q-alg
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The categories of this paper are: funct-an
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The categories of this paper are: q-fin
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The categories of this paper are: solv-int
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The categories of this paper are: alg-geom
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The categories of this paper are: q-bio
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The categories of this paper are: cmp-lg
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The categories of this paper are: nucl-th
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The categories of this paper are: atom-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: physics