Profile of the HCO⁺ 1–0 line observed in the L1157-B1 shock. The line intensity is in mean beam temperature (T_mb) and the systemic velocity (V_LSR = + 2.6 km s^-1) is indicated by the vertical dotted lines. The line profile is fitted by a linear combination of three exponential functions g₁ = I₁(0) exp(−|V/12.5 km s^-1|) (blue dotted line), g₂ = I₂(0) exp(−|V/4.4 km s^-1|) (red dashed line), and g₃ = I₃(0) exp(−|V/2.5 km s^-1)| (dotted-dashed black line). The (g₁ + g₂ + g₃) line fit is overplotted (magenta solid line).