a) S1S2 observed calibrated squared visibilities secured at four different pulsation phases plotted as a function of the spatial frequency together with the best fit of uniform disk model (solid blue line). In the upper right corner we show the corresponding (u,v) coverage. b) Same data fitted with a two-component model (open symbols) including a uniform pulsating disk and a CSE (see text). As a comparison, the solid lines are the corresponding one-component models, i.e. a uniform pulsating disk (in the R band) without the CSE.