  In this paper, we present a simple, one-step, self-consistent, and fast
resonance scattering model rsapec based on the AtomDB database. This model can
be used as an alternative to the commonly used APEC model for fitting such
X-ray spectra with optically thick lines. The current model is intended, in
general, for verifying the presence of the effect and for spectral modeling of
galaxy clusters and elliptical galaxies under applicable assumptions. We test
rsapec to derive the line suppression in the elliptical galaxy NGC 4636 and the
Perseus cluster of galaxies and obtain resonance suppression of ~ 1.24 and ~
1.30, respectively.
