Measured expansion velocities of simultaneously observed molecular lines according to radial distances from the central star for 11 HCN detected sources. The distances of the dominant line formation region in units of stellar radius from the central star are as follows. SiO maser adopted 3 R_* as the median value between 2 and 4 R_* (P. Diamond et al. 1994; D. A. Boboltz & M. Wittkowski 2005), H₂O maser adopted 36 R_* (A. Richards et al. 2012) and 120 R_* for HCN, 210 R_* for the SiS, 440 R_* for the SiO thermal lines, and 1300 R_* for CO based on the median values measured by S. Wallström et al. (2024). These values are indicated at the top of the graph. The vertical dashed line indicates dust condensation radius, R_dust at ∼6 R_* derived by C. A. Gottlieb et al. (2022).