Spectrum of the primary (black) and the companion at the best illuminated pixel as given in the central panel of Fig. 3 (red; with OH lines), together with the spectrum after subtracting the average spike east and west of the companion (blue), which contributes about 30% of the light (beforehand). While the H-band spectrum presents a triangular shape and bluer colour, indicating a young sub-stellar companion, the full continuum of the companion is not reliable because different amounts of flux are superimposed by the rotating primary spike, which changes the overall continuum shape because of the different spike removal quality.