Gas kinetic temperature derived from para-NH₃ (black points) and dust temperature (red points) along the W 40 region (projected distance from its main stellar source OS1a, l = 28.79°, b = 3.49°). The blue and green lines are the expected relationships from a Stefan-Boltzmann law and modified Stefan-Boltzmann law (see Sect. 4.4), respectively, assuming OS1a is the dominant source with an approximate luminosity of 10^5.25 L_⊙ (Kuhn et al. 2010; Rumble et al. 2016).