Top and central panels: squared visibilities with the limb-darkening fit residuals (top and central panels) at the wavelength band 1.6004 ± 0.0036 μm. The continuous line in the top panel corresponds to the limb-darkening fit whose parameters are reported in Table 3. The black horizontal dashed lines in the central panel correspond to the value of 1σ, and the red line shows the value of 3σ. Bottom panel: closure phase data points of β Oph (Table 2) for all the wavelengths. The red data correspond to closure phase departures larger than 3σ (see Fig. 2). The horizontal dashed lines in the bottom panel display the zero or ± 180° values.