Synthetic spectra based on the dynamic models at phase 0.98 with piston velocities of 2 (green line), 4 (red line), and 6 km s^-1 (blue line), keeping the same parameter values as the ones contained in Table 7. The dotted line is the ISO/SWS spectrum of the star at phase 0.97, whereas the error bars in the N-band correspond to the MIDI fluxes at phase 0.98. Squares and triangles correspond to the photometric measurements of the star (see Table 4).