Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Analysis of UV and EUV emission from impacts on the Sun after 2011 June
  7 eruptive flare   On 2011 June 7 debris from a large filament eruption fell back to the Sun
causing bright ultraviolet (UV) and extreme ultraviolet (EUV) splashes across
the surface. These impacts may give clues on the process of stellar accretion.
The aim is to investigate how the impact emission is influenced by structures
in the falling ejecta and at the solar surface. We determine the UV and EUV
light curves of a sample of impacts. The ballistic impact velocity is estimated
from the ejection and landing times and, where possible, compared with the
velocity derived by tracking the downflows in SDO/AIA and STEREO/EUVI images.
Estimates of the column density before impact are made from the darkness of the
falling plasma in the 193 A channel. The impact velocities were between 230 and
450 km/s. All impacts produced bright EUV emission at the impact site but
bright UV was only observed when the impacting fragments reached the
chromosphere. There was no clear relation between EUV intensity and kinetic
energy. Low UV to EUV intensity ratios (I{UV}/I{EUV}) were seen (i) from
impacts of low column-density fragments, (ii) when splashes, produced by some
impacts, prevented subsequent fragments from reaching the chromosphere, and
(iii) from an impact in an active region. The earliest impacts with the lowest
velocity (~250 km/s) had the highest I{UV}/I{EUV}. The I{UV}/I{EUV} decreases
with impact velocity, magnetic field at the impact site, and EUV ionising flux.
Many of the infalling fragments dissipate above the chromosphere either due to
ionisation and trapping in magnetic structures, or to them encountering a
splash from an earlier impact. If the same happens in accreting stars then the
reduced X-ray compared to optical emission that has been observed is more
likely due to absorption by the trailing stream than locally at the impact
site.

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The categories of this paper are: physics
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The categories of this paper are: supr-con
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: ao-sci
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The categories of this paper are: patt-sol
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The categories of this paper are: gr-qc
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The categories of this paper are: nlin
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The categories of this paper are: adap-org
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The categories of this paper are: math
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The categories of this paper are: stat
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-fin
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The categories of this paper are: hep-th
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The categories of this paper are: acc-phys
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The categories of this paper are: funct-an