Spectrophotometric light curves of the three observation epochs (left, center, and right panels) obtained using 20 nm bins, as well as bins centered on the Na and K line features. The central wavelength of each bin (in nm) is indicated in the left panel. The light curves centerend on the alkali features are ordered by bin width (from top to bottom): 10, 5 and 2 nm. Residuals are shown below, in the same order as the light curves.