Census of the measured values of R_p/R_⋆ ratios in the four Spitzer/IRAC channels for HD 189733b obtained using three transit observations during visit 1 and 2 (blue circles, Désert et al. 2009), and visit 3 (red square; this work) with their 1σ error bars. The data point obtained for visit 3 has to be corrected from stellar spots (see text 4.5.3). The IRAC bandpasses for each channel are shown at the top with dotted line. The theoretical planet-to-star radius ratios with absorption by only water molecules or by only Rayleigh scattering are plotted in light blue and grey respectively.