Decomposition of the residual spectrum into broad and narrow components. The top panel is the transit residual, R, that can be calculated following Eq. (1). This is further split into the broad component (middle orange line) and the narrow component (bottom purple line). The broadened component is the out-of-transit stellar spectrum scaled by the transit depth, DF_*. The narrow component is the difference between the transit residual spectrum and the broadened component.