Panel A: ULTRACAM light curves shown with different colours fitted with the DH model and a cold spot overlaid with solid black lines. Residuals are shown in the lower panels. Panel B: Surface temperature map along the orbit. Panel C: Observed radial velocity curve of J1431 obtained by Strader et al. (2019) (black dots) and the ones predicted by the model (empty dots) connected with a solid line together with a sinusoidal fit (dotted line). Residuals are displayed in the lower panel. Here phase zero is the inferior conjunction of the companion star.