Computations were carried out on DEC workstations (Tübingen) and CRAY computers (Rechenzentrum der Universität Kiel). This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. This work was supported by use of the Data Base of Galactic Planetary Nebulae (www: http://ast2.uibk.ac.at ) at Innsbruck. This research was supported by the Deutsche Agentur für Raumfahrtangelegenheiten (DARA) / Deutsches Zentrum für Luft- und Raumfahrt (DLR) under grants 50 OR 9409 1 and 50 OR 9705 5.
© European Southern Observatory (ESO) 1999
Online publication: June 18, 1999