ABSTRACT
We treat in this chapter the physical background of dust emission. A single grain radiates according to Kirchhoff’s law and we strictly derive this law in section 6.1 under the assumption that a grain consists of an ensemble of coupled harmonic oscillators in thermal equilibrium. In section 6.2, we show how to compute the temperature to which a grain is heated in a radiation field and section 6.3 illustrate its emission. For evaluating the emission of very small grains, which are those whose temperature fluctuates, we have to know the specific heat and the internal energy of the dust material. We therefore investigate in section 6.4 the calorific properties of dust. Finally, section 6.5 presents examples of the emission of very small grains.
