Observations of star HD 149404 obtained on 2015-05-12. The top left panel shows , the top right panel shows , the bottom left panel shows P, and the bottom right panel shows θ_E. In each panel, red empty circles refer to the observations obtained with order-separating filter, and blue solid circles refer to the observations obtained without order separating filter, with a 41.4 nm wavelength bin size. The black solid line is their average obtained from Eqs. (17). The green solid line (in arbitrary units and identical in all panels) shows the stellar flux not corrected for instrument+telescope transmission function, and with a 0.7 nm bin size. Error bars due to photon noise are smaller than or comparable to the symbol size, but the shape of the SED may help to visualise how the photon-noise error bars, which are proportional to the inverse of the S/N, change with wavelength.