tokens: model fitting is extensively detailed in ( Chen et al. 2016 ). In Table 2 , the refined planet parameters for CoRoT-29b are given. The orbital period and the zero epoch are calculated by fitting a linear function to our two transit epochs together with literature epochs. The rest of parameters are calculated by individually fitting the light curve of each epoch, but also by jointly fitting both transits together. These values are compared to those in the discovery paper by Cabrera et al. (2015) . Fig. 3 White light curve of CoRoT-29b. It is a summation of all the color-shaded passbands as shown in Fig. 2. From top to bottom : (1) normalized flux ratio between CoRoT-29 and its reference star, together with the best-fitting model; (2) white light curve after removing the modeled systematics, for display purpose; (3, 4) best-fitting light-curve residuals. Fig. 4 Color light curves of CoRoT-29b. Left and right panels : data from July 31st, 2014 and July 8th 2015, respectively. The light curves are shown after removing the modeled systematics, and overplotted are the best-fitting light-curve models. Fig. 5 Transmission spectrum of CoRoT-29b. The dashed line indicates the best-fitting derived from the white light curve. Blue and red colors indicate the two observing epochs. The gray-shaded area marks the scale height. Within error bars the spectrum is flat. 4. Discussion and conclusions Figure 3 presents the white light curve for the two datasets. In the top panel the raw flux ratios between CoRoT-29 and the comparison star are shown, where effects of airmass and seeing are still present. In the middle panel of the same figure, the light curves have been normalized and all systematic effects, except the analytic transit model, have been removed. Overplotted to the data are our best fits to each of the transits. It is remarkable that even at the faint magnitude of the CoRoT-29 (), using GTC we are able to reach precisions down to 300 ppm in 5 min exposure time; this is a factor 2.2 above photon noise. The residuals of the transit fit do not show any clearly identifiable features attributable to red noise, or an unaccounted for planetary signal. To be sure that the decorrelation process is not removing real asymmetries in the transit curve, we have generated mock light curves introducing an asymmetry in the form of a stellar spot (not shown). In that case using the same fitting methodology and a symmetric transit, the asymmetry is recovered, and only when using an asymetric transit profile, taking into accout the stellar spot effects, are the residuals of the fit similar to those in Fig. 3 . To further explore possible transit anomalies, we plot in Fig. 4 the color light curves for each of our spectral bins for the two observed epochs. It can be seen that the symmetry of the transit is maintained over all spectral bins and in both epochs. The only exception would be on the bluest light curves from July 8th 2015, where deviations from the transit model
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