Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Distant Field BHB Stars III: Identification of a probable outer halo
  stream at Galactocentric distance r = 70 kpc   We present VLT-FORS1 spectra of a sample of 34 faint 20.0 < g* < 21.1 A-type
stars selected from the Sloan Digital Sky Survey Early Data Release, with the
goal of measuring the velocity dispersion of blue horizontal branch (BHB) stars
in the remote Galactic halo, R~80kpc. We show that colour selection with 1.08 <
u*-g* < 1.40 and -0.2 < g*-r* < -0.04 minimises contamination of the sample by
less luminous blue stragglers. In classifying the stars we confine our
attention to the 20 stars with spectra of signal-to-noise ratio > 15 per
Angstrom. Classification produces a sample of eight BHB stars at distances
65-102 kpc from the Sun (mean 80 kpc), which represents the most distant sample
of Galactic stars with measured radial velocities. The dispersion of the
measured radial component of the velocity with respect to the centre of the
Galaxy is 58+-15km/s. This value is anomalously low in comparison with measured
values for stars at smaller distances, as well as for satellites at similar
distances. Seeking an explanation for the low measured velocity dispersion,
further analysis reveals that six of the eight remote BHB stars are plausibly
associated with a single orbit. Three previously known outer halo carbon stars
also appear to belong to this stream. The velocity dispersion of all nine stars
relative to the orbit is only 15+-4 km/s. Further observations along the orbit
are required to trace the full extent of this structure on the sky.

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The categories of this paper are: supr-con
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The categories of this paper are: solv-int
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The categories of this paper are: plasm-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org
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The categories of this paper are: physics
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The categories of this paper are: math-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: bayes-an
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The categories of this paper are: funct-an
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The categories of this paper are: q-bio
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The categories of this paper are: mtrl-th
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The categories of this paper are: eess
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The categories of this paper are: chem-ph