Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The 1600 Angstrom Emission Bump in Protoplanetary Disks: A Spectral
  Signature of H$_{2}$O Dissociation   The FUV continuum spectrum of many accreting pre-main sequence stars,
Classical T Tauri Stars (CTTSs), does not continue smoothly from the
well-studied Balmer continuum emission in the NUV, suggesting that additional
processes contribute to the short-wavelength emission in these objects. The
most notable spectral feature in the FUV continuum of some CTTSs is a broad
emission approximately centered at 1600~\AA, which has been referred to as the
"1600 A Bump". The origin of this feature remains unclear. We have assembled
archival FUV spectra of 37 disk-hosting systems observed by the {\it Hubble
Space Telescope}. Clear 1600 A Bump emission is observed above the smooth,
underlying 1100-1800 A continuum spectrum in 19/37 Classical T Tauri disks in
the HST sample, with the detection rate in transition disks (8/8) being much
higher than in primordial or non-transition sources (11/29). We describe a
spectral deconvolution analysis to separate the Bump (spanning 1490~--~1690 A)
from the underlying FUV continuum, finding an average Bump luminosity,
$L$(Bump7 x 10^{29} erg s^{-1}. We find that the 1600 A Bump is characterized
by a peak wavelength of 1598.6 +/- 3.3 A.
  Contrary to previous studies, we find that this feature is inconsistent with
models of H2 excited by electron-impact. We show that this Bump emits roughly
10-80% of the total fluorescent H2 luminosity for stars with well-defined Bump
features. Energetically, this suggests that the carrier of the 1600 A Bump
emission is powered by Ly-a photons. We argue that the most likely mechanism is
Ly-a-driven dissociation of H2O in the inner disk, r < 2 AU. We demonstrate
that non-thermally populated H2O fragments can qualitatively account for the
observed emission (discrete and continuum), and find that the average
Ly-a-driven H2O dissociation rate is 1.7x 10^{42} water molecules s^{-1}.

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The categories of this paper are: acc-phys
31
The categories of this paper are: ao-sci
35
The categories of this paper are: mtrl-th
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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: bayes-an
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The categories of this paper are: physics
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The categories of this paper are: nlin
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The categories of this paper are: quant-ph
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The categories of this paper are: cs
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: cmp-lg
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The categories of this paper are: chem-ph
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The categories of this paper are: math-ph