Fractional abundances (left) and abundance ratios (right) of selected species. The observed isotopic ratios towards L1544 for HCN and CN, as well as towards L1498 for CN, are shown as hatched areas (right panel). The ¹⁵N atom is noted N., such that CN. matches C¹⁵N, etc. The dotted line shows the adopted reference elemental isotopic ratio, ¹⁴N/¹⁵N = 440 (Marty et al. 2011).