GTC/OSIRIS 16 Å bin transmission spectrum, zoomed at the Na (left) and K (right) doublets. The red line along with the purple shaded regions show the best model and its 1-σ/2-σ confidence levels retrieved from the 10 nm bin transmission spectrum. While it is too noisy to claim detections of the Na and K line cores, the data indeed hint at possible excess absorption at the Na doublet and the K D₁ line. The K D₂ line is located in the telluric oxygen-A band.