Top: closure phases (CP) observed on Achernar and computed from the best-fit CHARRON model (Table 6) as a function of the spatial frequency (for the longest projected baseline in the corresponding triangle configuration). Bottom: CP residuals from observations relative to the best-fit model in units of corresponding uncertainties. The horizontal dotted lines delimit the ±3σ region around zero (dashed line). Since the photosphere is only partially resolved, the CP signatures of fast rotation are weak (within ~± 1°).