Line and continuum variability of IRC+10216 in the FIR. Top panel: continuum-subtracted spectra at different epochs (see also Fig. C.2); the dotted lines represent the CO transitions. Bottom panel: sine-wave fit to the continuum variability at two selected wavelengths for a fixed pulsation period of 630 days (solid lines) and a free-period fit corresponding to 680 and 660 days for the blue and red dashed curves, respectively.