  We present ground state photoionization cross sections of atoms and ions
averaged over resonance structures for photoionization modeling of
astrophysical sources. The detailed cross sections calculated in the
close-coupling approximation using the R-matrix method, with resonances
delineated at thousands of energies, are taken from the Opacity Project
database TOPbase and the Iron Project, including new data for the low
ionization stages of iron Fe I--V. The resonance-averaged cross sections are
obtained by convolving the detailed cross sections with a Gaussian distribution
over the autoionizing resonances. This procedure is expected to minimize errors
in the derived ionization rates that could result from small uncertainties in
computed positions of resonances, while preserving the overall resonant
contribution to the cross sections in the important near threshold regions. The
detailed photoionization cross sections at low photon energies are complemented
by new relativistic distorted-wave calculations for Z<= 12, and from
central-field calculations for Z>12 at high energies, including inner-shell
ionization. The effective cross sections are then represented by a small number
of points that can be readily interpolated linearly for practical applications;
a Fortran subroutine and data are available. The present numerically averaged
cross sections are compared with analytic fits that do not accurately represent
the effective cross sections in regions dominated by resonances.
