Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Eta Carinae's Declining Outflow Seen in the UV, 2002-2015   Existing HST UV data offer many previously neglected clues to eta Car's
behavior since 2000. Here we examine a subset of observations with diverse
results. (1) The star's rapid change of state is confirmed by major changes in
UV absorption lines, circumstellar extinction, and other features. (2) N III]
1750 is one of the two most luminous emission features in eta Car's observable
spectrum, comparable to H-alpha. This and other semi-forbidden lines are useful
because they have no P Cyg absorption. (3) N III] multiplet ratios provide the
first direct diagnostic of gas densities in eta Car's outflow. They strongly
suggest that high-excitation lines originate in condensations within the
colliding-wind shocked region. The parameters imply that published models have
not adequately represented the essential small size scales. (4) In 2002-2004, a
very large amount of N III] emission had anomalous Doppler velocities from +400
to +1200 km/s. This is a mystery; we conjecture that it may have resulted from
a burst of mass ejection in the 2003.5 periastron event. Various other effects
are also difficult to explain and merit further investigation.

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The categories of this paper are: gr-qc
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The categories of this paper are: acc-phys
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The categories of this paper are: bayes-an
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The categories of this paper are: solv-int
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The categories of this paper are: physics
29
The categories of this paper are: funct-an
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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: alg-geom
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The categories of this paper are: cond-mat
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The categories of this paper are: econ
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The categories of this paper are: q-bio
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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: q-alg
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The categories of this paper are: nucl-th