Excess absorption maps of KELT-11 b as a function of orbital phase, binned every 0.2% in phase, with both lines from the Na D doublet coadded. The dashed horizontal black lines indicate the transit contact points T₁ to T₄ from the start (bottom) until the end (top) of the transit. The dashed horizontal/diagonal black lines represent where the stacked sodium line should appear according to the orbital velocity of the planet; they are not traced inside the transit. Left: excess absorption maps in the stellar rest frame. Right: excess absorption maps in the planetary rest frame. Excess absorption in the sodium lines originating in the planetary atmosphere is clearly visible as a red signature over the duration of the transit. The thick multicolor traces correspond to the noisy parts of the stellar spectrum in the core of the Na D lines.