Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Coronal Abundances in Orion Nebula Cluster Stars   Following the Chandra Orion Ultradeep Project (COUP) observation, we have
studied the chemical composition of the hot plasma in a sample of 146 X-ray
bright pre-main sequence stars in the Orion Nebula Cluster. We report
measurements of individual element abundances for a subsample of 86
slightly-absorbed and bright X-ray sources, using low resolution X-ray spectra
obtained from the Chandra ACIS instrument. The X-ray emission originates from a
plasma with temperatures and elemental abundances very similar to those of
active coronae in older stars. A clear pattern of abundances vs. First
Ionization Potential (FIP) is evident if solar photospheric abundances are
assumed as reference. The results are validated by extensive simulations. The
observed abundance distributions are compatible with a single pattern of
abundances for all stars, although a weak dependence on flare loop size may be
present. The abundance of calcium is the only one which appears to vary
substantially between stars, but this quantity is affected by relatively large
uncertainties. The ensemble properties of the X-ray bright COUP sources confirm
that the iron in the emitting plasma is underabundant with respect to both the
solar composition and to the average stellar photospheric values. Comparison of
the present plasma abundances with those of the stellar photospheres and those
of the gaseous component of the nebula, indicates a good agreement for all the
other elements with available measurements, and in particular for the high-FIP
elements (Ne, Ar, O, and S) and for the low-FIP element Si. We conclude that
there is evidence of a significant chemical fractionation effect only for iron,
which appears to be depleted by a factor 1.5--3 with respect to the stellar
composition.

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The categories of this paper are: acc-phys
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The categories of this paper are: patt-sol
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The categories of this paper are: cmp-lg
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The categories of this paper are: comp-gas
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The categories of this paper are: q-fin
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The categories of this paper are: math-ph
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The categories of this paper are: q-bio
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The categories of this paper are: adap-org
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The categories of this paper are: eess
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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: hep-th
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-ex
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The categories of this paper are: econ
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The categories of this paper are: math