MODELING AND DISTANCE DETERMINATION OF PLANETARY-NEBULAE

We have developed a self-consistent method to determine the physical p arameters of planetary nebulae (PN) and also their distances using the photo-ionization code CLOUDY. To constrain the models, observed emiss ion line ratios, IRAS fluxes, radio fluxes and angular diameters are u sed. The method has been tested by applying it to artificial data from a planetary nebula model. It can reproduce all distance independent p hysical parameters with good accuracy. It can also reproduce the dista nce and all distance dependent physical parameters, but for this an ac curate determination of the angular size is crucial. The method has be en further tested by applying it to a sample of five galactic bulge PN . Comparison of the distance independent physical parameters with publ ished data shows that they generally are in fair agreement. The determ ined distances to these PN have large error margins. However, both the individual distances and the average distance are in agreement with t he distance to the galactic bulge. We conclude that the method that is presented works, provided that good observational data are available, and that sufficient emission lines of various ionization stages are o bserved in the spectrum to constrain the model.