Planet-to-star flux contrast as a function of wavelength. The solid lines show three models with κ_e = 0.00−0.03 cm²/g, and P_n = 0.1−0.3 for the planet WASP-4b. The squares are the estimated band-weighted measurements for these models, and the black point at 2.16   μm represents our measurement with its error bars. Note that the red model point at 2.16   μm is overlapped by our measurement. The measurements in Beerer et al. (2011) are also shown at 3.6, and 4.5   μm. The transmission curves for the three filters are also shown for comparison as dotted lines. A color version of this figure is available in the electronic form.