Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: HST Spectroscopy of Spot 1 on the Circumstellar Ring of SN 1987A   We present ultraviolet and optical spectra of the first bright spot (PA = 29
degrees) on Supernova 1987A's equatorial circumstellar ring taken with the
Space Telescope Imaging Spectrograph. We interpret this spot as the emission
produced by radiative shocks that occur where the supernova blast wave strikes
an inward protrusion of the ring. The observed line widths and intensity ratios
indicate the presence of radiative shocks with velocities ranging from 100 to
250 km s^-1 entering dense (> 10^4 cm^-3) gas. These observations, and future
observations of the development of the spectra and line profiles, provide a
unique opportunity to study the hydrodynamics of radiative shocks.

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The categories of this paper are: bayes-an
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The categories of this paper are: cs
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The categories of this paper are: mtrl-th
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The categories of this paper are: atom-ph
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The categories of this paper are: supr-con
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The categories of this paper are: cmp-lg
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The categories of this paper are: chem-ph
3
The categories of this paper are: physics
5
The categories of this paper are: gr-qc
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The categories of this paper are: nucl-th
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The categories of this paper are: q-bio
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The categories of this paper are: q-alg
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The categories of this paper are: hep-ex
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The categories of this paper are: funct-an
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The categories of this paper are: econ
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The categories of this paper are: solv-int