Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Stokes IQUV Magnetic Doppler Imaging of Ap stars I. ESPaDOnS and NARVAL
  Observations   In this paper we describe and evaluate new spectral line polarisation
observations obtained with the goal of mapping the surfaces of magnetic Ap
stars in great detail. One hundred complete or partial Stokes IQUV sequences,
corresponding to 297 individual polarised spectra, have been obtained for 7
bright Ap stars using the ESPaDOnS and NARVAL spectropolarimeters. The targets
span a range of mass from approximately 1.8 to 3.4 solar mass, a range of
rotation period from 2.56 to 6.80 days, and a range of maximum longitudinal
magnetic field strength from 0.3 to over 4 kG. For 3 of the 7 stars, we have
obtained dense phase coverage sampling the entire rotational cycle. These
datasets are suitable for immediate magnetic and chemical abundance surface
mapping using Magnetic Doppler Imaging (MDI). For the 4 remaining stars,
partial phase coverage has been obtained, and additional observations will be
required in order to map the surfaces of these stars. The median
signal-to-noise ratio of the reduced observations is over 700 per 1.8 km\s
pixel. Spectra of all stars show Stokes V Zeeman signatures in essentially all
individual lines, and most stars show clear Stokes QU signatures in many
individual spectral lines. The observations provide a vastly improved data set
compared to previous generations of observations in terms of signal-to-noise
ratio, resolving power and measurement uncertainties. Measurement of the
longitudinal magnetic field demonstrates that the data are internally
consistent within computed uncertainties typically at the 50 to 100 sigma
level. Data are also shown to be in excellent agreement with published
observations and in qualitative agreement with the predictions of published
surface structure models. This study establishes the performance and stability
of the ESPaDOnS and NARVAL high-resolution spectropolarimeters during the
period 2006-2010.

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The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
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The categories of this paper are: alg-geom
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The categories of this paper are: q-fin
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The categories of this paper are: funct-an
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The categories of this paper are: cond-mat
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The categories of this paper are: chao-dyn
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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: patt-sol
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The categories of this paper are: physics
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The categories of this paper are: solv-int
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The categories of this paper are: hep-th
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The categories of this paper are: eess
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The categories of this paper are: atom-ph