Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Characterization of the umbra-penumbra boundary by the vertical
  component of the magnetic field -- Analysis of ground-based data from the
  GREGOR Infrared Spectrograph   The vertical component of the magnetic field ($B_\perp$) was found to reach a
constant value at the umbra-penumbra boundary of stable sunspots in a recent
statistical study of Hinode/SP data. The objective of this work is to verify
the existence of a constant value for $B_\perp$ at the umbra-penumbra boundary
from ground-based data in the near-infrared wavelengths and to determine its
value for GREGOR Infrared Spectrograph (GRIS) data. This is the first
statistical study on the Jurcak criterion with ground-based data, and we
compare it with the results from Hinode and HMI data. Eleven
spectropolarimetric data sets from the GRIS slit-spectograph containing stable
sunspots were selected from the GRIS archive (sdc.leibniz-kis.de). SIR
inversions including a polarimetric straylight correction are used to produce
maps of the magnetic field vector using the Fe 1564.8 and 1566.2 nm lines.
Averages of $B_\perp$ along umbra-penumbra boundaries are analyzed for the 11
data sets. Geometric differences between contours at the resulting
$B_\perp^{\rm const}$ value and contours in intensity, $\Delta P$, are
calculated. Averaged over the 11 sunspots, we find a value of
$B_\perp=1787\pm100$ gauss. Contours at $B_\perp=B_\perp^{\rm const}$ and
contours calculated in intensity maps match from a visual inspection and the
geometric distance $\Delta P$ was found to be on the order of 2 pixels.
Furthermore, the standard deviation between different data sets of averages
along umbra--penumbra contours is smaller for $B_\perp$ than for $B_\parallel$
by a factor of 2.4. Our results provide further support to the Jurcak criterion
with the existence of an invariable value $B_\perp^{\rm const}$ at the
umbra--penumbra boundary. We also found that the geometric difference, $\Delta
P$, between intensity contours and contours at $B_\perp=B_\perp^{\rm const}$
acts as an index of stability for sunspots.

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The categories of this paper are: q-alg
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The categories of this paper are: hep-lat
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The categories of this paper are: alg-geom
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-th
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The categories of this paper are: q-bio
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-ph
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The categories of this paper are: econ
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The categories of this paper are: gr-qc
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The categories of this paper are: plasm-ph
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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: cmp-lg
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-ex