  Young solar-type stars are known to be strong X-ray emitters and their X-ray
spectra have been widely studied. X-rays from the central star may play a
crucial role in the thermodynamics and chemistry of the circumstellar material
as well as in the atmospheric evolution of young planets. In this paper we
present model spectra based on spectral parameters derived from the
observations of young stars in the Orion Nebula Cluster from the Chandra Orion
Ultradeep Project (COUP). The spectra are then used to calculate new
photoevaporation prescriptions that can be used in disc and planet population
synthesis models. Our models clearly show that disc wind mass loss rates are
controlled by the stellar luminosity in the soft (100 eV - 1 keV) X- ray band.
New analytical relations are provided for the mass loss rates and profiles of
photoevaporative winds as a function of the luminosity in the soft X-ray band.
The agreement between observed and predicted transition disc statistics
moderately improved using the new spectra, but the observed population of
strongly accreting large cavity discs can still not be reproduced by these
models. Furthermore, our models predict a population of non-accreting
transition discs that are not observed. This highlights the importance of
considering the depletion of millimeter-sized dust grains from the outer disc,
which is a likely reason why such discs have not been detected yet.
