Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Primeval very low-mass stars and brown dwarfs -- VII. The discovery of
  the first wide M + L extreme subdwarf binary   I present the discovery of the first wide M + L extreme subdwarf binary
system Gaia J0452$-$36AB. The binary is located at a distance of
137.27$^{+0.68}_{-0.67}$ pc with a projected separation of 15828$\pm$78 au. I
classified Gaia J0452$-$36AB as esdM1 and esdL0 subdwarfs, respectively. Gaia
J0452$-$36AB have typical halo kinematics, metallicity of [Fe/H] $\approx
-1.4$, and temperature of $\sim$ 3550 and 2600 K, respectively. Gaia
J0452$-$36AB is a pair of very low-mass stars with masses of
0.151$^{+0.029}_{-0.019}$ and 0.0855$^{+0.0014}_{-0.0010}$ M$_{\odot}$, and is
a gravitationally bound system. I tested the metallicity consistency of
existing M subdwarf classification schemes with Gaia J0452$-$36AB and a sample
of M and L subdwarfs with known metallicity. I found that the metallicity of
each M subclass defined by the the metallicity index $\zeta_{\rm CaH/TiO}$ is
not consistent from mid to late M subtypes. Because late-type M and L subdwarfs
have dusty atmospheres and high surface gravity which have significant impacts
on CaH and TiO indices that used in the classification. The metallicity scale
of late-type M subdwarfs would be overestimated by the $\zeta_{\rm CaH/TiO}$
index. I discussed the mass range of M subdwarfs, and explained the lack of
late-type M extreme and ultra subdwarfs, and decreasing binary fraction from
sdM, to esdM, and usdM subclasses. The four M subclasses have different mass
ranges. The comparison between M subclasses is between populations in different
mass ranges. I also present the discovery of Ruiz 440-469B, an M8 dwarf wide
companion to a cool DA white dwarf, Ruiz 440-469.

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The categories of this paper are: nucl-th
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The categories of this paper are: math-ph
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The categories of this paper are: econ
2
The categories of this paper are: math
0
The categories of this paper are: hep-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-ex
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The categories of this paper are: supr-con
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The categories of this paper are: dg-ga
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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: stat
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The categories of this paper are: atom-ph
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The categories of this paper are: q-fin
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The categories of this paper are: alg-geom
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The categories of this paper are: q-bio