Broadening the Canonical Picture of EUV-Driven Photoevaporation of Accretion Disks

Photoevaporation driven by hydrogen-ionizing radiation, also known as extreme-ultraviolet (EUV), is a ubiq-uitous phenomenon throughout cosmic time and spatial scales, profoundly shaping lifetimes of various astro-physics objects. Focusing primarily on protoplanetary disks, this study construct an analytical phenomeno-logical model that incorporates the finite timescale of photoheating and photoionization. It offers reasonableestimates for the temperature, ionization, and velocity structures of EUV-photoevaporating disks as a functionof distance, across a broad range of the EUV emission rates and spectra. The model delineates EUV pho-toevaporation into the hard- and soft-spectrum classes, unveiling diverse hydrodynamical and thermochemicalstructures contingent upon the EUV environments. Notably, we observe deviations from the canonical picture ofEUV photoevaporation, particularly around low-mas stars. In these cases, the structures do not necessarily alignwith the traditional picture of fully ionized and isothermal winds with speeds ≈ 10 km s−1. While our model pre-dictions demonstrate general agreement with hydrodynamics simulations, further comprehensive comparisonsare still warranted. Furthermore, our model also provides insights into the energy efficiency of EUV photoevap-oration and sheds light on discrepancies regarding the effectiveness of X-ray photoevaporation in the literature.These findings highlight the importance of considering the finite timescale of photoheating and photoioniza-tion in both numerical models and observational data interpretation, especially concerning photoevaporation ofprotoplanetary disks around low-mass stars