Degree of skewness as a function of the column density of molecular hydrogen: δ_i = (V_i − V_H¹³CN)/ΔV_H¹³CN, where i = 1,2,3 is the ith component of HCN(1−0), and V_H¹³CN and ΔV_H¹³CN are the velocity and the line width of component 2 (F = 2 → 1, the strongest) of the isotopologue H¹³CN(1−0). Values of δV from observations of component 1 (F = 1 → 1), triangles; component 2 (F = 2 → 1), squares; component 3 (F = 0 → 1), pentagons. See also Table B.1 for component indices.