RADEX models for Per-emb 29. Fluxes of the SO₂ 14_0,14−13_1,13 transition for two different kinetic temperatures: 50 K (left) and 150 K (right). The white contour represents the flux observed for this source and the dashed cyan contour shows an H₂ number density of 10⁷ cm⁻³ (lower limit for n_H used in the calculations). In this example, the present a minimum value of 3 × 10¹⁴ cm⁻² (for T_ex = 150) and a maximum value of 1 × 10¹⁵ cm⁻² (for T_ex = 50), in a range between 10⁷ and 10⁹ cm⁻³.