  We study the role of dark and bright autoionizing states (AIS) in
photoionization and high harmonic generation (HHG) using a 1D helium model.
This model allows numerical integration of the time-dependent Schr\"odinger
equation beyond the singe-electron approximation completely taking into account
electronic correlation. We find the level structure of the system and the
spatial distribution of the electronic density for several states including
AIS. Studying the HHG efficiency as a function of the detuning from the
resonances with AIS we find the HHG enhancement lines. The shapes of these
lines are different from the corresponding Fano lines in the photoelectronic
spectra, in agreement with the experimental studies in helium. Moreover, we
simulate HHG under the conditions when the fundamental frequency is close to
the even-order multiphoton resonance with the dark AIS. We find the enhanced
generation of the neighbouring odd harmonics. The details of the enhancement
lines for these harmonics can be understood taking into account the temporal
delay between the emission of the non-resonant and resonant XUV; this delay is
defined by the AIS lifetime. Finally, our simulations show that the HHG
enhancement due to the dark and the bright AIS is comparable in the studied
system.
