Motivated by recent work indicating that the UV continuum in AGN may be produced by reradiation of energy absorbed from X-rays irradiating an accretion disk , we present a calculation of the vertical structures and ultraviolet spectra of X-ray irradiated accretion disks around massive non-rotating black holes .
After finding the radial dependence of vertically-integrated quantities for these disks , we solve the equations of hydrostatic equilibrium , energy balance , and frequency-dependent radiation transfer as functions of altitude .
To solve the last set of equations , we use a variable Eddington factor method .
We include electron scattering , free-free , and HI , HeI , and HeII bound-free opacities and the corresponding continuum cooling processes .

The incident X-ray flux heats a thin layer of material 3-4 scale heights above the midplane of the disk .
This X-ray heated skin has two layers : a radiation pressure supported region in which the UV flux is created , and , immediately above this layer , a warmer zone , optically thin to UV radiation , formed where the X-ray ionization parameter is large .
In the lower layer the gas pressure is nearly independent of altitude but the temperature increases upward .

The fraction of the incident hard X-ray flux which emerges in the UV falls with increasing \dot { m } ( the accretion rate in Eddington units ) .
At frequencies below the Lyman edge the slope of the continuum ( d \ln L _ { \nu } / d \ln \nu ) varies from -1.6 to 0.8 as \dot { m } / m _ { 8 } increases from 0.001 to 1 .
Here m _ { 8 } is the mass of the central black hole in units of 10 ^ { 8 } M _ { \odot } .
In all cases examined ( 0.003 \leq \dot { m } \leq 0.3 and 0.27 \leq m _ { 8 } \leq 27 ) , the Lyman edge appears in emission .
The amplitude of the Lyman edge feature increases with m _ { 8 } but is relatively independent of \dot { m } .
The amplitude of the Lyman edge emission feature increases with disk inclination .
Compton scattering in disk coronae can smooth the Lyman edge feature only if \tau _ { c } \mathrel { \raise 1.29 pt \hbox { $ > $ \kern - 7.5 pt \lower 4.3 pt \hbox { $ \sim$ } } } 0.5 , where \tau _ { c } is the Thomson depth of the coronae .

While the overall spectral shape predicted by X-ray irradiation may be compatible with observations , the Lyman edge emission feature it predicts is not .
This finding raises questions for many otherwise plausible models in which X-ray irradiation plays a major role .