All Figures

$\begin{figure} \par\includegraphics[width=8.3cm,clip]{4576f1.eps} \end{figure}$ Figure 1: Fit for a typical low polarization (internetwork) pixel (pixel 151,151) of the 7 December 2003 map. The central line is Fe I 6302.5 Å, adjacent to a telluric line. Full line: observed intensity and polarization profiles. Dotted line: UNNOFIT result. The obtained magnetic field strength is 1619 Gauss and the magnetic filling factor $\alpha = 0.012$ , leading to the significant local average magnetic field strength $\alpha B = 19$ Gauss. The field inclination is 52 $^{\circ }$ and the azimuth is 36 $^{\circ }$ with respect to the slit direction. The wavelength pixels 28-33 that correspond to the telluric line have been discarded from the fitting procedure. The chi-square value, summed over the four Stokes parameters and the 31 analyzed wavelength pixels, is 0.0021 in polarization units (i.e., all the Stokes parameters having been divided by the continuum intensity).
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In the text

$\begin{figure} \includegraphics[width=12cm,clip]{4576f2.eps} \end{figure}$ Figure 2: Minimum of $\chi$ for two varying parameters: the magnetic filling factor (in abscissae, logarithmic scale) and the magnetic field strength (in ordonnae), for the same pixel as in Fig. 1. The other parameters of the model have been taken at their $\chi ^{2}$ -minimum value. The color scale has been limited to an $\chi$ variation inside the polarimetric sensitivity per pixel, 0.0015, divided by the square root of the total number of frequency pixels entering the $\chi$ calculation, namely $31\times 4$ pixels.
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In the text

$\begin{figure} \includegraphics[width=11.4cm,clip]{4576f3.eps} \end{figure}$ Figure 3: Minimum of $\chi$ for two other varying parameters that are the two angles defining the field vector direction: the inclination (in abscissae), and the azimuth (in ordonnae, defined modulo 180 $^{\circ }$ ), for the same pixel as in Fig. 2. The other parameters of the model have been taken at their $\chi ^{2}$ -minimum value. The color scale was limited to an $\chi$ variation inside the polarimetric sensitivity per pixel, 0.0015, divided by the square root of the total number of frequency pixels entering the $\chi$ calculation, namely $31\times 4$ pixels.
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=7.4cm,clip]{4576f4a.eps}\hspace{... ...ps}\hspace{0.4cm}\includegraphics[width=7.4cm,clip]{4576f4d.eps} }\end{figure}$ Figure 4: Comparison between the UNNOFIT output values with the input ones given as a series of values in a file (see text) for the line Fe I 6302.5. For each ensemble of input values (abscissae), a set of theoretical profiles has been computed, noised, and then inverted, leading to the output values (ordonnae). Upper row: left: magnetic field strength; right: magnetic filling factor. Lower row: local average magnetic field strength, which is the product of the magnetic field strength by the magnetic filling factor, the right figure being a zoom on the left one. The figure demonstrates that, although the magnetic field strength and magnetic filling factor are not separately recovered by the inversion, their product is recovered.
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In the text

$\begin{figure} \par\includegraphics[width=17.4cm,clip]{4576f5.eps} \end{figure}$ Figure 5: Accuracy of the UNNOFIT inversion (Fe I 6302.5 line): histograms of the differences between the UNNOFIT output values and the input ones given as a series of values in a file (see text). For each ensemble of input values, a set of theoretical profiles has been computed, noised, and then inverted, leading to the output values. Histograms have been plotted for 1/ the local average magnetic field strength, which is the product of the magnetic field strength by the magnetic filling factor, 2/ the line-of-sight inclination angle, and 3/ the slit azimuth angle. The histograms have been plotted for local average magnetic field strength higher and lower than 45 Gauss separately, corresponding on the maps to network and internetwork values, respectively.
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=7.4cm,clip]{4576f6a.eps}\hspace{... ...ps}\hspace{0.4cm}\includegraphics[width=7.4cm,clip]{4576f6d.eps} }\end{figure}$ Figure 6: Same as Fig. 4, but now for the Fe I 6301.5 line.
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In the text

$\begin{figure} \par\includegraphics[width=17.4cm,clip]{4576f7.eps} \end{figure}$ Figure 7: Same as Fig. 5, but now for the Fe I 6301.5 line: accuracy of the UNNOFIT2 inversion.
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In the text

$\begin{figure} \par\includegraphics[width=9cm,clip]{4576f8.eps} \end{figure}$ Figure 8: Source function as a function of the line optical depth as the result of a non-LTE solution in zero magnetic field in a Quiet Sun model atmosphere. Upper figure: logarithmic scales; lower figure: linear scales, showing a linear behavior compatible with the Milne-Eddington atmosphere in the low $\tau$ region. Such a solution has been used to test the validity of the Milne-Eddington approximation used by UNNOFIT. The atmosphere temperature is plotted on the right y-axis. The height ranges from -451 km below $\tau _{5000}=1$ (right of the figure) to 2140 km above $\tau _{5000}=1$ (left of the figure).
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{4576f9.eps} \end{figure}$ Figure 9: H $\alpha$ THEMIS map of 7 December 2003. In the upper part: active region NOAA 517. The scan was centered 17.5 $^{\circ }$ W in longitude and 12.9 $^{\circ }$ S in latitude from the disk center. The map size is $240\times 340$ arcsec. The slit, which defines the vertical axis of the figure, was oriented Solar North.
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In the text

$\begin{figure} \par\includegraphics[width=17.8cm,clip]{4576f10.eps} \end{figure}$ Figure 10: NOAA 517 local average vector magnetic field map from Fe I 6302.5 Å line (THEMIS 7 December 2003 observation, inverted with UNNOFIT). The longitudinal component is represented following the color scale (cold colors - blue, green - for fields entering the Sun, warm colors - red, yellow - for fields leaving the Sun). The transverse field is represented by scaled dashes, without arrow because the fundamental ambiguity is not solved. The dash scale is drawn at the right side of the figure, and its value is the largest transverse field strength of the map. The contours draw the limit $\alpha B=45$ Gauss, which is found to separate the network from the internetwork. In the internetwork the local average field is too small to be drawn, letting the ground H $\alpha$ map to be visible.
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In the text

$\begin{figure} \par\includegraphics[width=17.8cm,clip]{4576f11.eps} \end{figure}$ Figure 11: NOAA 517 local average vector magnetic field map from Fe I 6301.5 Å line (THEMIS 7 December 2003 observation, inverted with UNNOFIT2; same legend as Fig. 10). The contours are those derived from Fe I 6302.5.
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In the text

$\begin{figure} \par\includegraphics[width=17.8cm,clip]{4576f12.eps} \end{figure}$ Figure 12: Map of the magnetic field line-of-sight inclination angles of Fig. 10. The angle is the one between the magnetic field vector and the line-of-sight oriented towards the observer, from 0 $^{\circ }$ - blue, the field vector points towards the observer - to 180 $^{\circ }$ - yellow, the field vector points towards the disk center -. The contour of the H $\alpha$ filament has been superimposed.
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In the text

$\begin{figure} \par\includegraphics[width=17cm,clip]{4576f13.eps} \end{figure}$ Figure 13: Histograms of the local average magnetic field strength and direction from the Fe I 6302.5 Å line, for the full NOAA 517 map divided in 3 horizontal scans stacked up in the histograms in the same order, combining pixels having either the local average magnetic field strength, which is the product of the magnetic field strength by the magnetic filling factor, larger than 45 Gauss (network field), or lower than 45 Gauss (internetwork field).
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In the text

$\begin{figure} \par\includegraphics[width=16.4cm,clip]{4576f14.eps} \end{figure}$ Figure 14: Histograms of the local average magnetic field strength and direction from the Fe I 6301.5 Å line, for the full NOAA 517 map divided in 3 horizontal scans stacked up in the histograms in the same order, combining pixels having either the local average magnetic field strength, which is the product of the magnetic field strength by the magnetic filling factor, larger than 45 Gauss in Fe I 6302.5 Å (network field), or lower than 45 Gauss in Fe I 6302.5 Å (internetwork field).
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In the text

$\begin{figure} \par\includegraphics[width=14.8cm,clip]{4576f15.eps} \end{figure}$ Figure 15: Histograms of the differences in the Fe I 6301.5 Å results and Fe I 6302.5 Å results for the full NOAA 517 map divided in 3 horizontal scans stacked up in the histograms in the same order and combining pixels having either the local average magnetic field strength, which is the product of the magnetic field strength by the magnetic filling factor, larger than 45 Gauss in Fe I 6302.5 Å (network field), or lower than 45 Gauss in Fe I 6302.5 Å (internetwork field).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{4576f16.eps} \end{figure}$ Figure 16: 3D plot of the local average magnetic field strength through the Fe I 6302.5 Å map of Fig. 10. The internetwork is a sort of 20 Gauss ground on which the network emerges.
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=7.4cm,clip]{4576f6a.eps}\hspace{... ...ps}\hspace{0.4cm}\includegraphics[width=7.4cm,clip]{4576f6d.eps} }\end{figure}$	Figure 6: Same as Fig. 4, but now for the Fe I 6301.5 line.
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$\begin{figure} \par\includegraphics[width=17.4cm,clip]{4576f7.eps} \end{figure}$	Figure 7: Same as Fig. 5, but now for the Fe I 6301.5 line: accuracy of the UNNOFIT2 inversion.
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$\begin{figure} \par\includegraphics[width=8.4cm,clip]{4576f9.eps} \end{figure}$	Figure 9: H $\alpha$ THEMIS map of 7 December 2003. In the upper part: active region NOAA 517. The scan was centered 17.5 $^{\circ }$ W in longitude and 12.9 $^{\circ }$ S in latitude from the disk center. The map size is $240\times 340$ arcsec. The slit, which defines the vertical axis of the figure, was oriented Solar North.
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$\begin{figure} \par\includegraphics[width=17.8cm,clip]{4576f11.eps} \end{figure}$	Figure 11: NOAA 517 local average vector magnetic field map from Fe I 6301.5 Å line (THEMIS 7 December 2003 observation, inverted with UNNOFIT2; same legend as Fig. 10). The contours are those derived from Fe I 6302.5.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{4576f16.eps} \end{figure}$	Figure 16: 3D plot of the local average magnetic field strength through the Fe I 6302.5 Å map of Fig. 10. The internetwork is a sort of 20 Gauss ground on which the network emerges.
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