Interferometric observables, squared visibilities V² in the H band (left), and Brγ differential phases (right), computed for the pure photospheric model (black solid line) and for the two residual-disk models as defined in Table 5 at the upper limit values of ρ₀ (cf. Fig. 4): 0.52 × 10^-12 g cm^-3 (thin disk; blue solid line) and 0.65 × 10^-12 g cm^-3 (thick disk; blue dashed line). The baseline position angle PA was chosen to lie along the stellar equator (cf. Sect. 4.2), so that the effects of the residual disk are maximized on these comparisons. The baseline length for the differential phase calculations roughly corresponds to half of the maximum available length. Bottom: the difference between the interferometric observables from the disk models relative to the photospheric model. The shaded areas correspond to the typical observational errors from our PIONIER and AMBER observations. These difference plots show that the disk contribution to the interferometric observables is only a small fraction of the observation errors even at the upper limit ρ₀, discarding any detectable influence of a circumstellar disk on the present interferometric observations of Achernar.