Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical and near-infrared observations of the microquasar V4641
  Sagittarii during the 1999 September outburst   We present photometric and spectroscopic optical and near-infrared (NIR)
observations (Based on observations collected at the European Southern
Observatory, Chile (ESO ID 63.H-0493 and 64.H-0382)) taken during the outburst
of the microquasar V4641 Sgr = SAX J1819.3-2525 (in'tzand et al., 2000) in
September 1999. We observed an increase in the J-Ks colour between 5 and 8 days
after the outburst, which we interpret as likely evidence for the presence of
dust around the source. We also observed an extraordinarily strong, broad and
variable H_alpha line, with a velocity width of 4560 km/s suggesting the
presence of a high-velocity outflow component. We constrain the distance of the
system between 3 and 8 kpc, locating it further away than previously derived
from radio observations (Hjellming et al., 2000), but consistent with Orosz et
al. (2001). We then discuss the nature of this system, showing that the
companion star is either a B3-A2 main sequence star, or a B3-A2 sub-giant
crossing the Hertzsprung gap. The system is therefore an Intermediate or High
Mass X-ray Binary System (IMXB or HMXB). The distance derived by these
optical/NIR observations implies that the jets observed by Hjellming et al.
(2000) would then exhibit apparent velocities of ~ 10 c. We finally discuss the
possibility of an interaction between the jets and surroundings of the source,
and also of this source being a ``microblazar''.

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The categories of this paper are: comp-gas
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The categories of this paper are: stat
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The categories of this paper are: cond-mat
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The categories of this paper are: bayes-an
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-th
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The categories of this paper are: math-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: dg-ga
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The categories of this paper are: econ
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The categories of this paper are: supr-con
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The categories of this paper are: hep-lat