Transmission curves and residuals of the Na I D₁ (top) and K I line (bottom) for a Jupiter-sized planet transiting a Sun-like star at b = 0, using different models and the SST data to compute the stellar spectrum, as in legend. The relative flux is computed in a bandwidth of 0.75 Å around the line center. The residuals are the difference between the curve given by the SST data and the models in percentage.