Top panel: Contrast light curves of the first and second CO band head wavelengths with kernel smoothing applied. The pink lines show the fitted sinusoids to each band head. The third band head is shown in Fig. A.2. Bottom panel: Histogram of the distribution of the fitted periods between 0 and 10 h. The probability density for each band head and the total distribution of all band heads are shown. The expected rotation period and its two smaller harmonics are denoted by vertical black lines. The median period is shown in pink and coincides with P/2.