AMBER observation of HD 163296 with three different baselines (45.0 m: red upper line, 57.5 m: green middle line, and 81.6 m: blue lower line) and spectral resolution R = 12 000. From top to bottom: wavelength dependence of flux, visibilities, wavelength-differential phases, and closure phases. For clarity, the differential phases of the first and last baselines are shifted by +30 and −30°, respectively. The results shown correspond to the averaged value over three different observations (see Sect. 2 and Appendix for details). The wavelength scale is with respect to the local standard of rest (LSR) and corrected by a cloud velocity of ~8 km s^-1 (Isella et al. 2007).