Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Activity at the Deuterium-Burning Mass Limit in Orion   We report very intense and variable Halpha emission (pseudo-equivalent widths
of ~180, 410 A) of S Ori 55, a probable free-floating, M9-type substellar
member of the young sigma Orionis open star cluster. After comparison with
state-of-the-art evolutionary models, we infer that S Ori 55 is near or below
the cluster deuterium-burning mass borderline, which separates brown dwarfs and
planetary-mass objects. We find its mass to be 0.008-0.015 Msun for ages
between 1 Myr and 8 Myr, with ~0.012 Msun the most likely value at the cluster
age of 3 Myr. The largest Halpha intensity reached the saturation level of log
L(Halpha)/L(bol) = -3. We discuss several possible scenarios for such a strong
emission. We also show that sigma Orionis M and L dwarfs have in general more
Halpha emission than their older field spectral counterparts. This could be due
to a decline in the strength of the magnetic field with age in brown dwarfs and
isolated planetary-mass objects, or to a likely mass accretion from disks in
the very young sigma Orionis substellar members.

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The categories of this paper are: acc-phys
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The categories of this paper are: alg-geom
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The categories of this paper are: quant-ph
1
The categories of this paper are: cs
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The categories of this paper are: solv-int
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The categories of this paper are: hep-th
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The categories of this paper are: q-fin
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The categories of this paper are: ao-sci
18
The categories of this paper are: econ
0
The categories of this paper are: hep-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
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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: cmp-lg
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The categories of this paper are: plasm-ph