Excitation temperatures of H¹³CN(1−0) versus HN¹³C(1−0) evaluated from observations of L1498 (yellow squares), L1521E (green circles), and TMC 2 (black triangles). The dashed and solid black lines trace the values for T_ex computed using RADEX for kinetic temperatures, T_kin, of 6 and 10 K, respectively; red empty circles and red solid circles show temperatures where number density assumes values equal to 10⁴ and 10⁵ cm^-3 for T_kin = 6 K and 10 K, respectively. The dotted black line depicts the positions where the two excitation temperatures would be equal.