Photoevaporation from Inner Protoplanetary Disks Confronted with Observations

The decades-long explorations on the dispersal of protoplanetary disks involve many debates about photoevaporation versus magnetized wind launching mechanisms. This work argues that the observed winds originating from the inner disk (R ≲ 0.3 au) cannot be explained by the photoevaporative mechanism. Heating the gas to proper temperatures for the observed forbidden lines (especially [O i] λ6300) will overionize it, suppressing the abundances of species responsible for the emission. Even if adequate emissivity is achieved by fine-tuning the physical parameters, the total cooling power will become unattainable by the radiative heating alone. Energy conservation requires the presumed photoevaporative winds to be heated to ≳10⁵ K when launched from inner disks. However, due to efficient thermal accommodation with dust grains and cooling processes at high densities, X-ray irradiation at energies above 1 keV cannot efficiently launch winds in the first place because of its high penetration. Some studies claiming X-ray wind launching have oversimplified the thermochemical couplings. Confirmed by semianalytic integrations of thermochemical fluid structures, such high ionizations contradict the observed emission of neutral and singly ionized atoms from the winds originating from the inner disks.