All Figures

$\begin{figure} \par\includegraphics[width=16.1cm,clip]{AA4482-f1} \end{figure}$ Figure 1: DOT images of a quiet-Sun area below a quiescent filament. Top left: G band. Top right: Ca II H core. Bottom left: blue H $\alpha$ wing at $\Delta \lambda = -0.08$ nm from line center. The lower greyscale limit is defined by dark mottle endings and is therefore clipped to restore the bright point visibility. Bottom right: H $\alpha$ line center. A gap in the filament lies at the center of the field. Axes: x = geocentric East-West, y = geocentric North-South, with arbitrary offsets. The first three images were taken simultaneously, the fourth 30 s earlier. The white rectangles outline small subfields used in Figs. 2 and 3. The lefthand one samples quiet network, the righthand one more active network.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{AA4482-f2} \end{figure}$ Figure 2: Cut-out image magnifications corresponding to the righthand rectangle in Fig. 1. The four images were taken simultaneously. Top left: G band. Top right: Ca II H line center. Bottom left: near-H $\alpha$ red continuum at 650.0 nm. Bottom right: blue H $\alpha$ wing. Notice the bright point at (x,y) = (66.7,42.2) in H $\alpha$ , which barely shows up in the G band and is not present in Ca II H.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{AA4482-f3} \end{figure}$ Figure 3: Cut-out image magnifications and time slices corresponding to the lefthand outline sampling quiet network in Fig. 1, from left to right for the G band, Ca II H, and the H $\alpha$ wing. Top row: subfield images. The lefthand one of the two H $\alpha$ bright points is less evident at the other wavelengths. The white ticks indicate the horizontal cut along which the temporal evolution is shown below. Bottom row: $x\!-\!t$ time slices. The white ticks indicate the time sampled by the images above, which is 9 min after the full-field samples in Fig. 1.
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In the text

$\begin{figure} \par\includegraphics[width=16.4cm,clip]{AA4482-f4} \end{figure}$ Figure 4: NLTE H $\alpha$ wing formation in a vertical x-z slice through the MHD simulation. The first two columns illustrate H $\alpha$ bright point formation. The third column quantifies departures from LTE. The color scales are specified per panel in the bars to the right. The first and second rows show vertical stratifications on the common geometrical height scale (z axis). The bottom row shows individual stratifications against the logarithm of the radial optical depth along each column for $\Delta \lambda = -0.08$ nm from line center. The superimposed curves specify the mean height of formation for the intensity at $\Delta \lambda = -0.08$ nm from line center (upper curve) and in the background continuum at H $\alpha$ (lower curve). Panel 1: absolute value of the magnetic field strength. Panels 2 and 3: temperature against height and optical depth. Note the difference in temperature range. Panel 4: logarithm of the gas density against height. Panel 5: intensity contribution ${\rm d}I / {\rm d}z$ at $\Delta \lambda = -0.08$ nm from line center. Units: 10^-13 J m^-3 s^-1 Hz^-1 sr^-1. Panel 6: logarithm of the population density of the lower level of H $\alpha$ as a fraction of the total hydrogen density; Panels 7 and 8: NLTE population departure coefficients for the lower and upper levels of H $\alpha$ . Panel 9: ratio of the H $\alpha$ source function S and the Planck function B against optical depth.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{AA4482-f5} \end{figure}$ Figure 5: H $\alpha$ wing intensity computed from the 2D simulation in Fig. 4. Black solid curves: NLTE. Grey curves: LTE. Top: monochromatic intensity at $\Delta \lambda = -0.08$ nm from line center. The dashed higher-value curve is for the background continuum intensity at H $\alpha$ . Bottom: computed intensity with spectral integration over the DOT H $\alpha$ passband.
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In the text

$\begin{figure} \par\includegraphics[width=17.2cm,clip]{AA4482-f6}\end{figure}$ Figure 6: Illustration explaining the difference between H $\alpha$ and Ca II H wing formation. Top left: FALC temperature (lefthand scale, solid) and density (righthand scale, dotted). Bottom left: number density of the lower level of the line relative to the total number density of the atomic species, respectively for H $\alpha$ (lefthand scale, solid) and for Ca II H (righthand scale, dotted). Top center: line center extinction coefficient for H $\alpha$ (solid) and Ca II H (dotted). Bottom center: line center optical depth for H $\alpha$ (solid) and Ca II H (dotted). Top right: intensity contribution function for $\Delta \lambda = 0$ (solid), -0.038 (dotted), and -0.084 nm (dashed) from line center in H $\alpha$ . Squares indicate the $\tau = 1$ height. Bottom right: the same for Ca II H, at $\Delta \lambda = 0$ (solid), -0.024 (dotted), and -0.116 nm (dashed) from line center.
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In the text

$\begin{figure} \par\includegraphics[width=8.2cm,clip]{AA4482-f7} \end{figure}$ Figure 7: Demonstration of the H $\alpha$ opacity sensitivity to temperature with a hydrodynamic granulation simulation. Left: emergent intensity in the blue H $\alpha$ wing. The rms intensity variation is 0.047. Right: emergent intensity in the wing of a fake H $\alpha$ line at only 1 eV excitation. The rms intensity variation is 0.144, much larger than at left.
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In the text

$\begin{figure} \par\includegraphics[width=8.1cm,clip]{AA4482-f8} \end{figure}$ Figure 8: Results from the 3D MHD simulation. Top left: computed intensity in the H $\alpha$ wing. Top right: magnitude of the vector magnetic field at $\tau _{500} = 1$ . The grey scale ranges from 2 G to nearly 2 kG. The white contours are at 1 kG. Bottom left: simulated DOT H $\alpha$ wing image, obtained by convoluting the computed intensity pattern with the Airy point-spread function corresponding to 45-cm aperture diameter. The grey scale was set to the same range as the H $\alpha$ image in Fig. 2. Bottom right: similar simulated DOT image but for the continuum at 650 nm and grey-scaled to its dynamic range.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{AA4482-f9} \end{figure}$ Figure 9: Top: H $\alpha$ spectra. Solid grey: solar atlas profile. Dotted: spatially averaged spectrum from the 3D LTE simulation. Dash-dotted: average bright-point spectrum from the simulation. The narrow Gaussian shows the location and shape of the H $\alpha$ filter passband used in our H $\alpha$ wing observations. Bottom: average bright-point intensity divided by the average granule intensity, versus wavelength. Solid: unsmeared simulation. Dotted: simulation after convolution with the DOT-diameter Airy function. The asterisk specifies the observed contrast.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{AA4482-f5} \end{figure}$	Figure 5: H $\alpha$ wing intensity computed from the 2D simulation in Fig. 4. Black solid curves: NLTE. Grey curves: LTE. Top: monochromatic intensity at $\Delta \lambda = -0.08$ nm from line center. The dashed higher-value curve is for the background continuum intensity at H $\alpha$ . Bottom: computed intensity with spectral integration over the DOT H $\alpha$ passband.
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$\begin{figure} \par\includegraphics[width=8.2cm,clip]{AA4482-f7} \end{figure}$	Figure 7: Demonstration of the H $\alpha$ opacity sensitivity to temperature with a hydrodynamic granulation simulation. Left: emergent intensity in the blue H $\alpha$ wing. The rms intensity variation is 0.047. Right: emergent intensity in the wing of a fake H $\alpha$ line at only 1 eV excitation. The rms intensity variation is 0.144, much larger than at left.
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