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Fig. 8

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Difference between the umbral brightness (in temperature units) and the QS brightness, plotted as a function of wavelength for the model (i) of Avrett (1981), (ii) model M of Maltby et al. (1986), (iii) of Severino et al. (1994), (iv) model A of Socas-Navarro (2007), (v) model S of Fontenla et al. (2009) and (vi) the two-component umbral model of Obridko & Staude (1988) employing a filling factor of 0.05 for the hot component. Filled and open circles mark the observational values obtained from BIMA maps at 3.5 mm for the big and small umbrae, respectively. Arrowheads mark the shift of umbral brightness when extrapolating to 4′′ resolution. Diamonds stand for the measurements from JCMT at 0.35, 0.85 and 1.2 mm made by Lindsey & Kopp (1995).

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