4 Conclusion

In conclusion we'd like to reiterate a point already made in Paper I: due to the extreme heterogeneity of the class each PN is, to a certain extent, unique. So every new addition is well worth studying in detail, despite the more than 1000 galactic PNe known. The new objects presented here vividly illustrate this. Of the six objects in our sample three show signs of interaction with the ISM. They rank among the smallest but also most promising examples yet identified. In fact their small angular size should make them very good targets for further study by spectroscopy and narrow-band CCD imaging despite their low surface brightness. A solid observational base combined with further theoretical study will definitely be able to help better understand this process that seems to be much more common and important in the late stages of PN evolution than once thought. Additionally it provides a unique opportunity to study the properties of the ISM.

Acknowledgements

We want to thank R. Weinberger and S. Kimeswenger for their support and fruitful discussions. Special thanks are also due to the members of the staff at Las Campanas Observatory for their assistance and hospitality. We gratefully acknowledge the financial support by the "Fonds zur Förderung der wissenschaftlichen Forschung''; project P10279-AST and a travel grant from the Austrian "Bundesministerium für Wissenschaft, Transport und Kunst''. This research has made use of the Simbad database, operated at CDS, Strasbourg, France.