Medium-resolution LM-band observations of the Be binary δ Cen with GRA4MAT. The figure, already presented in Lopez et al. (2022), illustrates the improved instantaneous spectral coverage when operating with the fringe tracker. The long GRA4MAT-enabled DITs allow the full LM bands to be captured, whereas MATISSE standalone is limited to a width of 0.16 µm, corresponding to the grey outline for a Brα central wavelength. Top to bottom: chromatic flux, clean fringes as observed on the LM-band detector, chromatic squared visibility, chromatic phase.