Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An analysis of ultraviolet spectra of Extreme Helium Stars and new clues
  to their origins   Abundances of about 18 elements including the heavy elements Y and Zr are
determined from Hubble Space Telescope Space Telescope Imaging Spectrograph
ultraviolet spectra of seven extreme helium stars (EHes): LSE 78, BD+10 2179,
V1920 Cyg, HD 124448, PV Tel, LS IV -1 2, and FQ Aqr. New optical spectra of
the three stars -- BD+10 2179, V1920 Cyg, and HD 124448 were analysed. The
abundance analyses is done using LTE line formation and LTE model atmospheres
especially constructed for these EHe stars. The stellar parameters derived from
an EHe's UV spectrum are in satisfactory agreement with those derived from its
optical spectrum. Adopted abundances for the seven EHes are from a combination
of the UV and optical analyses. Published results for an additional ten EHes
provide abundances obtained in a nearly uniform manner for a total of 17 EHes,
the largest sample on record. The initial metallicity of an EHe is indicated by
the abundance of elements from Al to Ni; Fe is adopted to be the representative
of initial metallicity. Iron abundances range from approximately solar to about
one-hundredth of solar. Clues to EHe evolution are contained within the H, He,
C, N, O, Y, and Zr abundances. Two novel results are (i) the O abundance for
some stars is close to the predicted initial abundance yet the N abundance
indicates almost complete conversion of initial C, N, and O to N by the
CNO-cycles; (ii) three of the seven stars with UV spectra show a strong
enhancement of Y and Zr attributable to an s-process. The observed compositions
are discussed in light of expectations from accretion of a He white dwarf by a
CO white dwarf.

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The categories of this paper are: hep-lat
33
The categories of this paper are: plasm-ph
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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: alg-geom
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The categories of this paper are: eess
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The categories of this paper are: hep-th
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The categories of this paper are: math-ph
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The categories of this paper are: funct-an
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The categories of this paper are: nucl-ex
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The categories of this paper are: nucl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-ph
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The categories of this paper are: q-fin
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The categories of this paper are: acc-phys
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The categories of this paper are: stat