Contribution of hydrogen and helium to the total heating and cooling rates. Top panels: heating (left) and cooling (right) rates as a function of the radius r. The red line in the left panel and the blue line in the right panel correspond to the total rates, while the green and yellow shaded areas correspond to the total hydrogen and helium rates, respectively. The green(yellow) solid and dashed lines correspond to the rates of H(He) I, II, respectively, while the yellow dot-dashed line to He III. Bottom: hydrogen and helium (left and right, respectively) ion abundances (see legend for colour-coding) as a function of r. In all cases log() = 1, t = 10² s.