General Overview

The creation of ATOMDB allows users to open up the "black box" of atomic data needed to calculate the emission from an optically-thin thermal plasma. The FITS files in the APED directory of the ATOMDB effectively contain all the information used by APEC to calculate the emission spectrum; APEC contains no hard-coded atomic data (with the sole exception of photoionization cross sections of hydrogenic ions).

The APED directory in ATOMDB contains multiple sources for some atomic data. The APEC models in ATOMDB use a selected subset of these data, based on critical evaluation by members of the APEC collaboration.

The spectral files output from APEC separate the spectrum into line and continuum emission; therefore, the resolution of the model spectrum is purely the choice of the final user, not set by the value used when the code was run. APEC files may be used to determine the theoretical dependence of spectral components on model parameters. Examples include individual line emissivities as a function of temperature or density, the contribution of a given element to the continuum spectrum at a single temperature, and the spectrum of lines arising from a single upper level.