Top: intensity maps calculated for selected wavelengths inside the Hα line (from left to right): 6559.5 Å, 6561.3 Å, 6562.8 Å, and 6565.2 Å. Ordinates and abscissas are given in units of the equatorial radius R_eq. The inclination angle used is i = 55°. Bottom: photo-center displacements along the y-axis (left side); differential phase associated with the photo-center shift (right side). All quantities are computed for a sixty-meter baseline parallel to the equatorial axis (x-axis). The photo-center displacements are given in units of the angular stellar radius.