Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A census of very-low-mass stars and brown dwarfs in the sigma Orionis
  cluster   (ABRIDGED) We have analysed the near-infrared photometric data from the
Fourth Data Release (DR4) of the UKIRT Infrared Deep Sky Suvey (UKIDSS)
Galactic Clusters Survey (GCS) to derive the cluster luminosity and mass
functions, evaluate the extent of the cluster, and study the distribution and
variability of low-mass stars and brown dwarfs down to the deuterium-burning
limit. We have recovered most of the previously published members and found a
total of 287 candidate members within the central 30 arcmin in the 0.5-0.009
Msun mass range, including new objects not previously reported in the
literature. This new catalogue represents a homogeneous dataset of brown dwarf
member candidates over the central 30 arcmin of the cluster. The expected
photometric contamination by field objects with similar magnitudes and colours
to sigma Orionis members is ~15%. We present evidence of variability at the
99.5% confidence level over ~yearly timescales in 10 member candidates that
exhibit signs of youth and the presence of disks. The level of variability is
low (<0.3 mag) and does not impact the derivation of the cluster luminosity and
mass functions. Furthermore, we find a possible dearth of brown dwarfs within
the central five arcmin of the cluster, which is not caused by a lower level of
photometric sensitivity around the massive, O-type multiple star sigma Ori in
the GCS survey. Using state-of-the-art theoretical models, we derived the
luminosity and mass functions within the central 30 arcmin from the cluster
centre, with completeness down to J = 19 mag, corresponding to masses ranging
from 0.5 Msun down to the deuterium-burning mass boundary (~0.013 Msun). The
mass function of sigma Orionis in this mass interval shows a power law index
alpha = 0.5+/-0.2.

37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
18
The categories of this paper are: econ
26
The categories of this paper are: bayes-an
31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
11
The categories of this paper are: hep-lat
35
The categories of this paper are: mtrl-th
28
The categories of this paper are: alg-geom
34
The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph
14
The categories of this paper are: math-ph
15
The categories of this paper are: nucl-ex
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs