Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High-Resolution Spectra Observed for SPY. II. DB and DBA Stars   We present a detailed spectroscopic analysis of the stars with
helium-dominated spectra in the ESO Supernova Ia Progenitor Survey (SPY).
Atmospheric parameters, masses, and abundances of trace hydrogen are determined
and discussed in the context of spectral evolution of white dwarfs. Our final
sample contains 71 objects, of which 6 are new detections and 14 are
reclassified from DB to DBA because of the presence of H lines. 55% of the DB
sample show hydrogen and are thus DBA, a significantly higher fraction than
found before. The large incidence of DBA, and the derived total hydrogen masses
are compatible with the scenario that DBs ``reappear'' around 30000 K from the
DB gap by mixing and diluting a thin hydrogen layer of the order of E-15 Msun.
This hydrogen mass is then during the evolution continuously increased by
interstellar accretion. There are indications that the accretion rate increases
smoothly with age or decreasing temperature, a trend which continuous even
below the current low temperature limit (Dufour 2006). A remaining mystery is
the low accretion rate of H compared to that of Ca observed in the DBZA, but a
stellar wind extending down to the lowest temperatures with decreasing strength
might be part of the solution.

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The categories of this paper are: econ
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The categories of this paper are: adap-org
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-fin
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The categories of this paper are: bayes-an
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The categories of this paper are: eess
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The categories of this paper are: patt-sol
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The categories of this paper are: chao-dyn
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The categories of this paper are: ao-sci
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The categories of this paper are: physics
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The categories of this paper are: math
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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: hep-lat
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The categories of this paper are: comp-gas
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The categories of this paper are: cmp-lg