Measured values of R_p/R_⋆ ratios at 3.6 μm as fonction of the relative decrease of stellar flux due to spots (in V-band). The blue and red squares are the R_p/R_⋆ derived from the observations of visit 1 and 3 respectively. The dotted line corresponds to the theoretical correction of the relative difference between the measured radius ratio and the expected value as function of the relative decrease of stellar flux in the V-band f_λ. Using ground based photometric follow-up (Fig. 10), we set f_{(3.6   μm)} to zero for visit 1 (see text 4.5.1). The R_p/R_⋆ we derive from the observations of visit 3 (no correction) is above the one obtained in visit 1 (4σ). To compare both visits, the R_p/R_⋆ derived from visit 3 has to be corrected for spots (Sect. 4.5.3). Simultaneous observation in V-band shows that f_V − band =  −2% during visit 3 (Fig. 10). (R_p/R_⋆)_Corrected for visit 3 agree with R_p/R_⋆ derived in visit 1 for a slope α =  −3.