  The analysis of Planetary Nebulae (PNe) provides a tool to investigate the
properties of their exciting central stars (CSPN) at the moment of the PN
ejection as well as on the properties of the ambient interstellar medium (ISM).
The spectral analysis of the CSPN is a prerequisite to calculate the ionizing
flux which is a crucial input for reliable PN modeling. In the framework of a
systematic study of PNe interacting with the ISM, we present preliminary
results of ongoing NLTE spectral analyses of ten of their CS based on new
optical medium-resolution spectra.
