Top: periodogram for the K2 light curve of ρ Oph C. The rotational| frequencies of ρ Oph Ab and C are indicated by long, thick blue and red dashes; harmonics of these frequencies are indicated by short dashes of the same colours. Significant frequencies that are not harmonics of either of the rotational frequencies are indicated by green dashes. The pre-whitened periodogram is shown in light green. The purple curve shows the noise model determined from the pre-whitened periodogram; the dashed curve indicates 4× the noise. Bottom panels: light curves of ρ Oph A (left) and C (right), folded with their rotational frequencies and pre-whitened with all frequencies unrelated to the star’s rotation. Curves show harmonic models.