  We investigate the origin of the broad absorption features detected near
1-1.4 keV in several Narrow Line Seyfert 1 galaxies, by modelling the absorbing
medium with various physical parameters, using the ionization code PEGAS. The
observed properties of the X-ray absorption features can be reproduced by
taking into account the peculiar soft X-ray excess which is well fitted by a
blackbody plus an underlying power law. We equally stress that the emission
coming from the absorbing medium (related to the covering factor) has a strong
influence on the resulting X-ray spectrum, in particular on the apparent
position and depth of the absorption features. A non-solar iron abundance may
be required to explain the observed deep absorption. We also investigate the
influence of an additional collisional ionization process (hybrid case) on the
predicted absorption features.
