Observational constraints on disk photoevaporation by the central star

We apply results from FUV and X-ray spectroscopy to evaluate the role of photoevaporation in dispersing the disk around TW Hya. Accretion produces bright EUV emission that may be smothered by the accretion column. Solar-like magnetic activity produces fewer ionizing photons, which may be absorbed by an accretion-powered neutral wind. We estimate a photoevaporation rate of ∼ 5 × 10⁻¹¹M_⊙ yr⁻¹ for the disk around TW Hya. These models can be tested by detecting gas in the ionized disk surface, including emission in the [Ne II] 12.8μm line. Photoevaporation is likely a minor process in disk dispersal during the accretion phase, but could remove ∼ 1 M_J of remnant gas around a solar-mass star after accretion ceases.