Contours of χ² of the overall fits of the photometric data. The blue and red dots correspond to the best fits for the entire set of V, y and c₂-band data, and to the V and y data alone, respectively. The cyan and magenta contours provide the corresponding confidence levels for the full dataset and for the sole V and y data, respectively. The open square with error bars corresponds to our best-fit result of the equivalent RV data.