We present new X-ray and Far Ultraviolet ( FUV ) observations of T Tauri stars covering the age range 1 to 10 Myr .
Our goals are to observationally constrain the intensity of radiation fields responsible for evaporating gas from the circumstellar disk and to assess the feasibility of current photoevaporation models , focusing on X-ray and UV radiation .
We greatly increase the number of 7–10 Myr old T Tauri stars observed in the X-rays by including observations of the well populated 25 Ori aggregate in the Orion OB1a subassociation .
With these new 7–10 Myr objects , we confirm that X-ray emission remains constant from 1–10 Myr .
We also show , for the first time , observational evidence for the evolution of FUV radiation fields with a sample of 56 accreting and non-accreting young stars spanning 1 Myr to 1 Gyr .
We find that the FUV emission decreases on timescales consistent with the decline of accretion in classical T Tauri stars until reaching the chromospheric level in weak T Tauri stars and debris disks .
Overall , we find that the observed strength of high energy radiation is consistent with that required by photoevaporation models to dissipate the disks in timescales of approximately 10 Myr .
Finally , we find that the high energy fields that affect gas evolution are not similarly affecting dust evolution ; in particular , we find that disks with inner clearings , the transitional disks , have similar levels of FUV emission as full disks .