Production and loss rates of He(2³S) (labelled as in Table 2, left y-axis) for the case of 6000 K and a mass-loss rate of 4.2 × 10⁹ g s⁻¹. The blue line corresponds to the production by recombination and the red lines to the losses. Also shown are the concentrations of the species directly involved in the recombination (right-y axis): the electrons (in cm⁻³, black solid line) and the [He⁺]/[He] ratio (scaled by 5 × 10⁸ in cyan). An H/He ratio of 90/10 was assumed.