Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Four nearby L dwarfs   We present spectroscopic, photometric and astrometric observations of four
bright L dwarfs identified in the course of the 2MASS near-infrared survey. Our
spectroscopic data extend to wavelengths shortward of 5000\AA in the L0 dwarf
2MASSJ0746+2000 and the L4 dwarf 2MASSJ0036+1840, allowing the identification
of absorption bands due to MgH and CaOH. The atomic resonance lines Ca I
4227\AA and Na I 5890/5896\AA are extremely strong, with the latter having an
equivalent width of 240\AA in the L4 dwarf. By spectral type L5, the D lines
extend over $\sim1000$\AA and absorb a substantial fraction of the flux emitted
in the V band, with a corresponding effect on the (V-I) broadband colour. The
KI resonance doublet at 7665/7699\AA increases in equivalent width from
spectral type M3 to M7, but decreases in strength from M7 to L0 before
broadening substantially at later types. These variations are likely driven by
dust formation in these cool atmospheres.

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The categories of this paper are: hep-th
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The categories of this paper are: eess
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The categories of this paper are: funct-an
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The categories of this paper are: math
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The categories of this paper are: mtrl-th
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The categories of this paper are: physics
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The categories of this paper are: q-bio
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The categories of this paper are: econ
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The categories of this paper are: cmp-lg
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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
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The categories of this paper are: q-alg
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The categories of this paper are: hep-ex
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The categories of this paper are: plasm-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: nlin