Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Low-resolution spectroscopy and spectral energy distributions of
  selected sources towards sigma Orionis   Aims: We investigated in detail nine sources in the direction of the young
sigma Orionis cluster, which is considered a unique site for studying stellar
and substellar formation. The nine sources were selected because of some
peculiar properties, such as extremely red infrared colours or too strong
Halpha emission for their blue optical colours. Methods: We took high-quality,
low-resolution spectroscopy (R ~ 500) of the nine targets with ALFOSC at the
Nordic Optical Telescope. We also re-analyzed [24]-band photometry from
MIPS/Spitzer and compiled the best photometry available at the ViJHKs passbands
and the four IRAC/Spitzer channels for constructing accurate spectral energy
distributions covering from 0.55 to 24 mum. Results: The nine targets were
classified into: one Herbig Ae/Be star with a scatterer edge-on disc, two
G-type stars, one X-ray flaring, early-M, young star with chromospheric Halpha
emission, one very low-mass, accreting, young spectroscopic binary, two young
objects at the brown dwarf boundary with the characteristics of classical T
Tauri stars, and two emission-line galaxies, one undergoing star formation, and
another one whose spectral energy distribution is dominated by an active
galactic nucleus. Besides, we discover three infrared sources associated to
overdensities in a cold cloud in the cluster centre. Conclusions:
Low-resolution spectroscopy and spectral energy distributions are a vital tool
for measuring the physical properties and the evolution of young stars and
candidates in the sigma Orionis cluster.

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The categories of this paper are: alg-geom
10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
26
The categories of this paper are: bayes-an
13
The categories of this paper are: quant-ph
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
12
The categories of this paper are: nucl-th
11
The categories of this paper are: hep-lat
8
The categories of this paper are: hep-ex
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
4
The categories of this paper are: cond-mat
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The categories of this paper are: eess
33
The categories of this paper are: plasm-ph