Spectra observed towards L1551-IRS5 (see Table A.4 in T_MB scale). Species, transition, and upper level energy are reported in each panel. The vertical dotted line stands for the source systemic velocity as measured using the C¹⁸O(2–1) line (+6.4 km s⁻¹). The vertical dashed line and the vertical dash-dotted line stand for the systemic velocities of the binary system associated with the southern source (+4.5 km s⁻¹) and northern source (+7.5 km s⁻¹), respectively. In the ¹³CS(5–4) spectrum the velocity scale is centered on the brightest (38 D²) hyperfine component (vertical blue line) at 231220.7 MHz; the vertical red lines indicate the offset in velocity of the fainter components (21 D² at 231220.7 MHz; 17 D² at 231220.6 MHz; 1 D² at 231220.5 MHz). In the C¹⁵N(2–1) spectrum (lower panel) the velocity scale is centered on the brightest (6 D²) hyperfine component (vertical blue line) at 219934.8 MHz; the vertical red lines indicate the offset in velocity of the fainter components (4 D² at 219934.0 MHz).