Top: Squared visibility data points (diamonds), along with the error bars. UD models fitted to the data points are shown in dotted lines. Middle: Squared visibility data simultaneously fitted with a wavelength‐independent UD star surrounded by a water molecular shell. While optical depths at 1.51 and 1.78 μm are treated as free parameters, the optical depth at 1.64 μm is fixed at zero. Bottom: Same as middle, except that optical depths at all three wavelengths are treated as free parameters.