Sketch (not to scale) of the model considered in this work. Despite the axis representation, the (0, 0) position corresponds to the star location. In the star reference frame, the ISM moves with velocity equal to V_⋆. The position of the contact discontinuity (CD), forward shock (FS), and reverse shock (RS) are shown in solid lines. The solid line with arrows coming from the star and entering into the shocked region represents one of the streamlines that conform the emitter. The inclination angle i and the position angle θ are also shown.