Top panel: image taken through the 40″ slit. WASP-39 is the left-hand bright star, and the comparison is the right-hand bright star. This panel is cropped vertically. Bottom panel: an example science frame. WASP-39 is the left-hand bright trace, and the comparison is the right-hand bright trace. The solid blue lines show the target aperture, and the dashed lines indicate the region over which the background was calculated.