We present the first radiation-hydrodynamic model of a protoplanetary disc irradiated with an X-EUV spectrum .
In a model where the total ionizing luminosity is divided equally between X-ray and EUV luminosity , we find a photoevaporation rate of 1.4 \times 10 ^ { -8 } M _ { \odot } yr ^ { -1 } , which is two orders of magnitude greater than the case of EUV photoevaporation alone .
Thus it is clear that the X-rays are the dominant driving mechanism for photoevaporation .
This can be understood inasmuch as X-rays are capable of penetrating much larger columns ( \sim 10 ^ { 22 } cm ^ { -2 } ) and can thus effect heating in denser regions and at larger radius than the EUV can .
The radial extent of the launching region of the X-ray heated wind is 1-70AU compared with the pure EUV case where the launch region is concentrated around a few AU .
When we couple our wind mass-loss rates with models for the disc ’ s viscous evolution , we find that , as in the pure EUV case , there is a photoevaporative switch , such that an inner hole develops at \sim 1 AU at the point that the accretion rate in the disc drops below the wind mass loss rate .
At this point , the remaining disc material is quickly removed in the final 15-20 % of the disc ’ s lifetime .
This is consistent with the 10 ^ { 5 } yr transitional timescale estimated from observations of T-Tauri stars .
We however note several key difference to previous EUV driven photoevaporation models .
The two orders of magnitude higher photoevaporation rate is now consistent with the average accretion rate observed in young stars and will cut the disc off in its prime .
Moreover , the extended mass-loss profile subjects the disc to a significant period ( \sim 20 % of the disc ’ s lifetime ) of ‘ photoevaporation starved accretion ’ .
We also caution that although our mass-loss rates are high compared to some accretion rates observed in young stars , our model has a rather large X-ray luminosity of 2 \times 10 ^ { 30 } erg s ^ { -1 } ; further modeling is required in order to investigate the evolutionary implications of the large observed spread of X-ray luminosities in T-Tauri stars .