Difference curves for Na iD₂ (left column) and D₁ (right column) for three feature bands with half-widths of 0.6 Å, 0.9 Å, and 1.5 Å (top to bottom). Top panels show the data and the model (solid, red line), and the bottom show the residuals. The line core (± 0.3 Å around the line center) has been excluded. The reference bands were 5840−5860 Å and 5925.875−5945.875 Å. The effect of the CLV is different in the two lines and it is weaker for broader spectral bands.