Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Discovery of the Earliest-Type Oe Stars in the Small Magellanic Cloud   No classical Oe/Be stars with spectral type earlier than O7.5e have been
identified to date in the Milky Way (MW). This is consistent with the decretion
disk model because strong stellar winds cause early-type O stars to lose
angular momentum, thereby preventing them from rotating fast enough to spin out
decretion disks. How- ever, metal-poor O stars have weaker stellar winds,
allowing the stars to retain angular momentum. Therefore, low-metallicity
environments should promote the formation of Oe stars, including those of
earlier spectral types than observed in high-metallicity en- vironments. Using
the RIOTS4 survey, a spatially complete spectroscopic survey of Small
Magellanic Cloud (SMC) field OB stars taken with the IMACS multi-slit spec-
trograph at the Magellan Baade Telescope, we identify 25-31 SMC field Oe stars,
which account for 20-28% of SMC field O stars. This fraction is significantly
higher than in the MW, where < 10-15% of O stars display the Be phenomenon. We
also present 5-7 Oe stars of spectral type ranging from O5.5e to O7e, all
earlier spectral types than the earliest MW Oe star. These early type Oe stars
represent 20-23% of our SMC Oe stars, a dramatic increase compared to the MW,
where no Oe stars have been identified with these early spectral types. Thus,
the higher frequencies of Oe stars and their earlier spectral range in the
metal-poor SMC are consistent with the decretion disk model.

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The categories of this paper are: cmp-lg
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The categories of this paper are: q-alg
2
The categories of this paper are: math
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The categories of this paper are: solv-int
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The categories of this paper are: stat
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: chem-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: cond-mat
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The categories of this paper are: nlin
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: econ
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The categories of this paper are: physics