Recombination structure of the RSG envelope at points A–F. The six colored circles show the radius of the RSG at points A–F. The coloring inside the circles shows the specific released recombination energy ϵ_rec as logmod(ϵ_rec/10³ erg s⁻¹ g⁻¹) on a linear radial scale, with logmod(x) = sign(x)log₁₀(|x|+1) (John & Draper 1980). Red corresponds to energy released by recombination, while blue corresponds to energy being removed via ionization. The square insets at each point show the recombination luminosity L_rec, i = ∫_Menvϵ_rec, i dm for the species i = H⁺,  He⁺ and He²⁺ on a linear scale. Hatched regions indicate the partial ionization zone for hydrogen and helium, defined where the ionization fraction of the corresponding species is between 1% and 99%. Light gray shading at points A and B corresponds to neutral layers (ionization fractions less than 1%). The central plot shows the radius evolution of one pulsation cycle and indicates the 6 highlighted points A–F. The temporal evolution of the recombination structure is available as an online movie.