Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Structure of the Outer Galactic Disc as revealed by IPHAS early A
  Stars   This study is an investigation of the stellar density profile of the Galactic
disc in the Anticentre direction. We select over 40,000 early A stars from
IPHAS photometry in the Galactic longitude range 160 < l < 200 close to the
equatorial plane (-1 < b < +1). We then compare their observed
reddening-corrected apparent magnitude distribution with simulated photometry
obtained from parameterised models in order to set constraints on the
Anticentre stellar density profile. By selecting A stars, we are appraising the
properties of a population only ~100 Myrs old. We find the stellar density
profile of young stars is well fit to an exponential with length scale of (3020
\pm 120_{statistical} \pm 180_{systematic}) pc, which is comparable to that
obtained in earlier studies, out to a Galactocentric radius of R_T = (13.0 \pm
0.5_{statistical} \pm 0.6_{systematic}) kpc. At larger radii the rate of
decline appears to increase with the scale length dropping to (1200 \pm
300_{statistical} \pm 70_{systematic}) pc. This result amounts to a refinement
of the conclusions reached in previous studies that the stellar density profile
is abruptly truncated. The IPHAS A star data are not compatible with models
that propose a sudden change in metallicity at R_G = 10 kpc.

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The categories of this paper are: cond-mat
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The categories of this paper are: math
1
The categories of this paper are: cs
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The categories of this paper are: solv-int
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The categories of this paper are: quant-ph
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The categories of this paper are: supr-con
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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: funct-an
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The categories of this paper are: hep-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: gr-qc
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The categories of this paper are: chem-ph
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The categories of this paper are: stat
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The categories of this paper are: nlin
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The categories of this paper are: comp-gas