The input parameters are the source spectrum, the gas composition, and the gas density
or pressure. The spectrum of the central source of radiation is described by the spectral
luminosity,
, where
is the total
luminosity (in erg s
). The spectral function,
,
is normalized such that
and
may be of one of a variety of types, including: Thermal bremsstrahlung,
; blackbody,
;
or power law,
; or the user
may define the form of the ionizing continuum by providing a table of
energies and fluxes. The gas consists of the elements H, He, C, N, O, Ne, Mg,
Si, S, Ar, Ca, Fe, and Ni with relative abundances specified by the user.
The default abundances are the solar values given by [Grevesse, Noels and Sauval 1996].