Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The HD 163296 Circumstellar Disk in Scattered Light: Evidence of
  Time-Variable Self-Shadowing   We present the first multi-color view of the scattered light disk of the
Herbig Ae star HD 163296, based on coronagraphic observations from the Hubble
Space Telescope Advanced Camera for Surveys (ACS). Radial profile fits of the
surface brightness along the disk's semi-major axis indicates that the disk is
not continuously flared, and extends to 540 AU. The disk's color (V-I)=1.1 at a
radial distance of 3.5 arcseconds is redder than the observed stellar color
(V-I)=0.15. This red disk color might be indicative of either an evolution in
the grain size distribution (i.e. grain growth) and/or composition, both of
which would be consistent with the observed non-flared geometry of the outer
disk. We also identify a single ansa morphological structure in our F435W ACS
data, which is absent from earlier epoch F606W and F814W ACS data, but
corresponds to one of the two ansa observed in archival HST STIS coronagraphic
data.
  Following transformation to similar band-passes, we find that the scattered
light disk of HD 163296 is 1 mag arcsec$^{-2}$ fainter at 3.5 arcseconds in the
STIS data than in the ACS data. Moreover, variations are seen in (i) the
visibility of the ansa(e) structures, in (ii) the relative surface brightness
of the ansa(e) structures, and in (iii) the (known) intrinsic polarization of
the system. These results indicate that the scattered light from the HD 163296
disk is variable. We speculate that the inner disk wall, which Sitko et al.
suggests has a variable scale height as diagnosed by near-IR SED variability,
induces variable self-shadowing of the outer disk. We further speculate that
the observed surface brightness variability of the ansa(e) structures may
indicate that the inner disk wall is azimuthally asymmetric.

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The categories of this paper are: hep-lat
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The categories of this paper are: cond-mat
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The categories of this paper are: bayes-an
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The categories of this paper are: econ
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The categories of this paper are: adap-org
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The categories of this paper are: cmp-lg
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The categories of this paper are: funct-an
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The categories of this paper are: solv-int
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The categories of this paper are: q-alg
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The categories of this paper are: plasm-ph
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The categories of this paper are: nlin
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The categories of this paper are: gr-qc
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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: patt-sol