Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical Spectroscopy of 2MASS Color-Selected Ultracool Subdwarfs   We present Gemini GMOS and Magellan LDSS-3 optical spectroscopy for seven
ultracool subdwarf candidates color-selected from the Two Micron All Sky
Survey. Five are identified as late-type subdwarfs, including the previously
reported sdM9.5 SSSPM 1013-1356 and L subdwarf 2MASS 1626+3925, and a new
sdM8.5 2MASS 0142+0523. 2MASS 1640+1231 exhibits spectral features intermediate
between a late-type M dwarf and subdwarf, similar to the previously identified
high proper motion star SSSPM 1444-2019, and we classify both sources as mild
subdwarfs, d/sdM9. 2MASS 1227-0447 is a new ultracool extreme subdwarf,
spectral type esdM7.5. Spectral model fits yield metallicities that are
consistent with these metallicity classifications. Effective temperatures track
with numerical subtype within a metallicity class, although they are not
equivalent across metallicity classes. As a first attempt to delineate subtypes
in the L subdwarf regime we classify 2MASS 1626+3925 and the previously
identified 2MASS 0532+8246 as sdL4 and sdL7, respectively, to reflect their
similarity to equivalently classified, solar metallicity L-type field dwarfs
over the 7300-9000 A region. We also detail preliminary criteria for
distinguishing L subdwarf optical spectra as a roadmap for defining this new
spectral class. The strong TiO bands and Ca I and Ti I lines in the spectrum of
2MASS 1626+3925 provide further evidence that condensate formation may be
inhibited in metal-deficient L subdwarfs. We conclude with a compendium of
currently known, optically classified ultracool subdwarfs.

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The categories of this paper are: eess
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The categories of this paper are: physics
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The categories of this paper are: q-fin
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The categories of this paper are: funct-an
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The categories of this paper are: econ
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The categories of this paper are: hep-lat
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The categories of this paper are: atom-ph
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The categories of this paper are: supr-con
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-th
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The categories of this paper are: bayes-an
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The categories of this paper are: cs
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The categories of this paper are: nucl-th
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The categories of this paper are: nlin
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The categories of this paper are: cmp-lg
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The categories of this paper are: chao-dyn