APEX spectra of the four sources toward which all three HCN J = 2 → 1 lines are detected. For each source, the upper, middle, and lower panels show the spectra for the (0,0,0), (0, 1 ^1_c, 0), and (0, 1^1_d, 0) lines, respectively. 1 K T_MB corresponds to a flux density of 33.4 Jy. To facilitate the comparison between the lines, we used the same intensity scale for the first two lines, except for CW Leo. In addition, for CW Leo, the T_MB scale of the dotted blue line shows the base of the (0, 1^1_c, 0) spectrum scaled up by a factor of 8 compared to the ordinate in that panel. To adequately display the weak (0, 1 ^1_d, 0) emission, a compressed T_MB scale is used for all sources for this line. The vertical dotted blue line marks the stellar velocity, while the dashed blue lines indicate the terminal velocity. The spectral line partially appearing in the (0, 1 ^1_d, 0) spectrum of IRC+10216 at velocities > 10 km s⁻¹ is part of a multiplet component of the N = 18 → 17 transition of C₃N.