Burkart Bovelet, Eberhard Wiehr
We determine the number density and area contribution of small-scale inter-granular Ca II bright G-band structures in images of the quiet Sun as tracers of kilo-Gauss magnetic flux-concentrations. In a 149 arcsec X 117 arcsec G-band image of the disk center at the activity minimum, 7593 small inter-granular structures were segmented with the `multiple-level tracking' pattern recognition algorithm. The scatter-plot of the continuum versus the G-band brightness shows the known magnetic and non-magnetic branches. These branches are largely disentangled by applying an intrinsic Ca II excess criterion. The thus obtained 2995 structures contain 1152 G-band bright points (BP) and 1843 G-band faint points (FP). They show a tendency toward increasing size with decreasing G-band excess, as expected from the `hot wall' picture. Their Ca H and G-band brightness are slightly related, resembling the known relation of Ca II and magnetic field strength. The magnetic flux density of each individual BP and FP is estimated from their G-band brightness according to MHD model calculations. The entity of BP and FP covers the total FOV with a number density of 0.32 Mm^2 and a total area contribution of 2.0%. Their individual calibrations yield a mean flux density of 20 Mx/cm^2 in the entire FOV and 13 cm^2 for inter-network regions.
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http://arxiv.org/abs/1208.2160
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