Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cool helium-rich white dwarfs from the Hamburg/ESO Survey   We present an analysis of 40 cool helium-rich white dwarfs found in the
Hamburg/ESO survey. They were selected for follow-up spectroscopy because of
their U-B colour below -0.18, the absence of strong absorption lines, and a
continuum shape similar to that of a quasar. Effective temperatures for
individual stars were determined by fitting model atmospheres of nearly pure
helium with a small admixture of hydrogen. As a consequence of the selection
criteria all but one sample stars have Teff below 20000 K. Four stars clearly
show helium and hydrogen lines in their spectra. In the spectra of another
three, helium, hydrogen, and metal lines can be detected. For these stars
hydrogen and metal abundances were also determined by fitting appropriate model
atmospheres containing these elements. Seven sample stars most likely have
helium-rich atmospheres but do not show any helium lines. They either have
featureless spectra or show calcium lines.

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The categories of this paper are: cond-mat
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The categories of this paper are: acc-phys
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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: nlin
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The categories of this paper are: solv-int
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The categories of this paper are: hep-ph
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The categories of this paper are: q-alg
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: gr-qc
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The categories of this paper are: comp-gas
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The categories of this paper are: q-bio
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The categories of this paper are: quant-ph
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The categories of this paper are: stat