Two-dimensional map of residuals for both Na I D₂ (left) and D₁ (right) lines for the first night. The green horizontal dashed lines show the times of first, second, third, and fourth contact and the diagonal dotted line represents the expected trail of the exoplanetary atmospheric absorption. In each panel, the vertical axis is time (similar to the exposure number). Blue and red colors stand for residual fluctuations in the direction of absorption and emission, respectively. The tested masked region is under the shaded area.