Mean energy of photoelectrons (asterisks, in eV) calculated with Eq. (4) and a corresponding thermal equilibrium temperature of 1.5 kT_e = Ē_{el, ph} (dashed line) versus the threshold of photoionization calculated for the SED of KELT-9. For the cross section, a simple formula is used: σ_ph-ion = σ_thr(E_thr/E)³, E > E_thr. The labeled vertical lines indicate the photoionization thresholds of several particular elements, or transitions, of interest.