Left: same as Fig. 2 but with a model composed of β Cep and an edge-on ring. Most data are from S1S2 short baseline (see nights 23/11/08 and 26/08/09), which help constrain the geometry of the ring and, in particular, its orientation on the sky. The image of the model is also provided. Right: the same but with a model composed of β Cep and a pole-on ring. In this case, we have more data for the W1W2 long baseline (see nights 31/07/08 and 08/10/08), which helps constrain the angular diameter of the β Cep.