Ma. Bautista et al., RESONANCE-AVERAGED PHOTOIONIZATION CROSS-SECTIONS FOR ASTROPHYSICAL MODELS, The Astrophysical journal. Supplement series, 118(1), 1998, pp. 259-265
We present ground-state photoionization cross sections of atoms and io
ns averaged over resonance structures for photoionization modeling of
astrophysical sources. The detailed cross sections calculated in the c
lose-coupling approximation using the R-matrix method, with resonances
delineated at thousands of energies, are taken from the Opacity Proje
ct database TOPbase and the Iron Project, including new data for the l
ow ionization stages of iron Fe I-Fe v. The resonance-averaged cross s
ections 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 c
ould result from small uncertainties in computed positions of resonanc
es while preserving the overall resonant contribution to the cross sec
tions in the important near-threshold regions. The detailed photoioniz
ation cross sections at low photon energies are complemented by new re
lativistic distorted-wave calculations for Z less than or equal to 12
and from central-held calculations for Z > 12 at high energies, includ
ing inner shell ionization. The effective cross sections are then repr
esented by a small number of points that can be readily interpolated l
inearly for practical applications; a FORTRAN subroutine and data are
available. The present numerically averaged cross sections are compare
d with analytic fits that do not accurately represent the effective cr
oss sections in regions dominated by resonances.