Scatter plot of the differences between the wavelength of the gravity center (λ_g) and the peak (λ_p) of Ca⁺IR vs. the differences of Doppler velocity between Ca⁺H and Ca⁺IR in the pixels that satisfy all the conditions described in Sect. 3. The linear Pearson correlation coefficient, r, is 0.65. The white vertical lines indicate the threshold of λ_g−λ_p of Ca⁺IR to exclude the highly asymmetric profiles to give the absolute value of the linear Pearson correlation coefficient of all combinations of the four lines to be less than 0.3.