Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Metallicity and the spectral energy distribution and spectral types of
  dwarf O-stars   We present a systematic study of the effect of metallicity on the stellar
spectral energy distribution (SED) of O main sequence (dwarf) stars, focussing
on the hydrogen and helium ionizing continua, and on the optical and near-IR
lines used for spectral classification. The spectra are based on non-LTE line
blanketed atmosphere models with stellar winds calculated using the CMFGEN code
of Hillier & Miller (1998). We draw the following conclusions. First, we find
that the total number of Lyman photons emitted is almost independent of line
blanketing effects and metallicity for a given effective temperature. This is
because the flux that is blocked by the forest of metal lines at wavelengths
shorter than 600 Angstrom is redistributed mainly within the Lyman continuum.
Second, the spectral type, as defined by the ratio of the equivalent widths of
HeI 4471 Angstrom and HeII 4542 Angstrom, is shown to depend noticeably on the
microturbulent velocity in the atmosphere, on metallicity and, within the
luminosity class of dwarfs, on gravity. Third, we confirm the decrease in the
effective temperature for a given spectral type due to the inclusion of line
blanketing recently found by e.g. Martins et al. (2002). Finally, we find that
the SED below ~450 Angstrom is highly dependent on metallicity. This is
reflected in the behaviour of nebular fine-structure line ratios such as
[NeIII]/[NeII] 15.5/12.8 and [ArIII]/[ArII] 9.0/7.0 micron. This dependence
complicates the use of these nebular ratios as diagnostic tools for the
effective temperature determination of the ionizing stars in HII regions and
for age dating of starburst regions in galaxies.

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The categories of this paper are: quant-ph
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The categories of this paper are: funct-an
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The categories of this paper are: plasm-ph
31
The categories of this paper are: ao-sci
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The categories of this paper are: cond-mat
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The categories of this paper are: adap-org
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The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: solv-int
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The categories of this paper are: math
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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: acc-phys
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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: nucl-th