Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: What's the nature of sdA stars?   White dwarfs with log g lower than 7.0 are called Extremely Low Mass white
dwarfs (ELMs). They were first found as companions to pulsars, then to other
white dwarfs and main sequence stars (The ELM Survey: 2010 to 2016), and can
only be formed in interacting binaries in the age of the Universe. In our SDSS
DR12 white dwarf catalog (Kepler et al. 2016), we found a few thousand stars in
the effective temperature and surface gravity ranges attributed to ELMs. We
have called these objects sdAs, alluding to their narrow hydrogen line spectra
showing sub-main sequence log g. One possible explanation for the sdAs is that
they are ELMs. Increasing the ELMs sample would help constrain the number of
close binaries in the Galaxy. Interestingly, if they turn out to be A stars
with an overestimated log g, the distance modulus would put these young stars
in the Galaxy's halo.

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The categories of this paper are: nucl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: alg-geom
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The categories of this paper are: atom-ph
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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: supr-con
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The categories of this paper are: cs
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The categories of this paper are: eess
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The categories of this paper are: physics
30
The categories of this paper are: q-alg
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol
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The categories of this paper are: math
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The categories of this paper are: hep-lat
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The categories of this paper are: math-ph