¹⁴N/¹⁵N ratio of CN in 4 positions across L1544. Left panel: H₂ column density map of L1544 computed from Herschel/SPIRE observations (Spezzano et al. 2016). The black crosses show the centre of the areas where the spectra shown in the right panel have been extracted. The black circles show the regions where the spectra shown in the right panel have been averaged. Right panel: spectra of ¹³CN (N, J, F₁, F = 1 3/2 2 3-0 1/2 1 2) in black and C¹⁵N (N, J, F= 1 3/2 2-0 1/2 1) in red, extracted towards the offsets marked in the left panel. The values in boldface in blue report the ¹⁴N/¹⁵N ratio in CN for each set of spectra derived using the ¹²CN column density directly from the spectra shown in Fig. B.1. The values in boldface in green report the ¹⁴N/¹⁵N ratio computed from the column density of ¹³CN using the ¹²C/¹³C ratio of 68 (Milam et al. 2005).