Fig. 8

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Average bisectors of quiet and active solar regions from the disk center (μ = 1.0) to the limb (μ = 0.2). Continuous lines: fifth-order polynomial fit to the quiet sun bisectors of the FeI 5250.2084, FeI 5250.6453, FeI 5434.5232, FeI 5432.9470, FeI 5576.0881, FeI 6149.2460, FeI 6173.3344, FeI 6301.5008, and FeI 6302.4932 Å lines as measured by the Laser Absolute Reference Spectrograph (LARS) at the German Vacuum Tower Telescope (Löhner-Böttcher et al. 2019). Dashed lines: fit of the bisectors of the FeI 6301.5008 Å spectral line inside a faculae region, as measured by the Fabry-Perot interferometer at the Donati Solar Tower (Cavallini et al. 1985a). Below a depth of 0.5, a linear fit is performed, while a fifht-order polynomial is used to model the top part of the bisector. To prevent unrealistic value when interpolating the polynomial above a normalised flux of 0.9 where no measurement exists, we selected the most redshifted part of the top bisector, explaining the vertical values for very shallow depths. The two vertical lines are shifted by 340 m s−1 which corresponds to the solar convective blueshift value derived from a fit to the data of Liebing et al. (2021, see Sect. 4.3.3). The active bisectors at different μ angles are all shifted by those 340 m s−1 at a depth of 0.58 based on our hypothesis that convection is fully suppressed in magnetic regions (see Sect. 4.3.2 for more information).
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