Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Multiplicity among T Tauri stars in OB and T associations: Implications
  for binary star formation   We present first results of a survey for companions among X-ray selected
pre-main sequence stars, most of them being weak-line T Tauri stars (WTTS).
These T Tauri stars have been identified in the course of optical follow-up
observations of sources from the ROSAT All Sky Survey associated with star
forming regions. The areas surveyed include the T associations of Chamaeleon
and Lupus as well as Upper Scorpius, the latter being part of the Scorpius
Centaurus OB association (Sco OB 2).
  Using SUSI at the NTT under subarcsec seeing conditions we observed 195 T
Tauri stars through a 1$\mu$m ("Z") filter and identified companions to 31 of
them (among these 12 subarcsec binaries). Based on statistical arguments we
conclude that almost all of them are indeed physical (i.e. gravitationally
bound) binary or multiple systems. For 10 systems located in Upper Scorpius and
Lupus, we additionally obtained spatially resolved near-infrared photometry in
the J, H, and K bands with the MPIA 2.2m telescope at ESO, La Silla. The
near-infrared colours of the secondaries are consistent with those of dwarfs
and are clearly distinct from those of late type giant stars. Based on
astrometric measurements of some binaries we show that the components of these
binaries are common proper motion pairs, very likely in a gravitationally bound
orbit around each other.
  We find that the overall binary frequency among T Tauri stars in a range of
separations between 120 and 1800 AU is in agreement with the binary frequency
observed among main sequence stars in the solar neighbourhood. However, we note
  that within individual regions the spatial distribution of binaries -- within
a distinct range of separation -- is non-uniform. In particular, in Upper

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The categories of this paper are: comp-gas
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The categories of this paper are: eess
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The categories of this paper are: mtrl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: cs
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The categories of this paper are: q-alg
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The categories of this paper are: cmp-lg
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The categories of this paper are: nucl-ex
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The categories of this paper are: stat
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The categories of this paper are: plasm-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: adap-org
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-lat
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The categories of this paper are: q-bio
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The categories of this paper are: dg-ga