Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Accretion Disc Winds in Tidal Disruption Events: Ultraviolet Spectral
  Lines as Orientation Indicators   Some tidal disruption events (TDEs) exhibit blueshifted broad absorption
lines (BALs) in their rest-frame ultraviolet (UV) spectra, while others display
broad emission lines (BELs). Similar phenomenology is observed in quasars and
accreting white dwarfs, where it can be interpreted as an orientation effect
associated with line formation in an accretion disc wind.We propose and explore
a similar unification scheme for TDEs. We present synthetic UV spectra for disc
and wind-hosting TDEs, produced by a state-of-the-art Monte Carlo ionization
and radiative transfer code. Our models cover a wide range of disc wind
geometries and kinematics. Such winds naturally reproduce both BALs and BELs.
In general, sight lines looking into the wind cone preferentially produce BALs,
while other orientations preferentially produce BELs. We also study the effect
of wind clumping and CNO-processed abundances on the observed spectra. Clumpy
winds tend to produce stronger UV emission and absorption lines, because
clumping increases both the emission measure and the abundances of the relevant
ionic species, the latter by reducing the ionization state of the outflow. The
main effect of adopting CNO-processed abundances is a weakening of C~{\sc
iv}~1550~\AA~ and an enhancement of N \textsc{v}~1240~\AA~ in the spectra. We
conclude that line formation in an accretion disc wind is a promising mechanism
for explaining the diverse UV spectra of TDEs. If this is correct, the relative
number of BAL and BEL TDEs can be used to estimate the covering factor of the
outflow. The models in this work are publicly available online and upon
request.

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The categories of this paper are: nucl-ex
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The categories of this paper are: q-alg
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The categories of this paper are: nlin
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The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: cs
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The categories of this paper are: atom-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: q-fin
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The categories of this paper are: cond-mat
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The categories of this paper are: comp-gas
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The categories of this paper are: alg-geom
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The categories of this paper are: ao-sci
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-th