I am greatly indebted to Dr. Albert Zijlstra for the motivation to present this study, and to Prof.Dr. Teije de Jong for his interest and stimulating discussions. I would like to thank Drs. Martin Groenewegen, Rens Waters, and Joana Oliveira for reading an earlier version of the manuscript, and Fred Marang for the excellent support during the near-IR observations at Sutherland. I also thank Prof.Dr. Harm Habing and Dr. Peter Wood for sharing their results prior to publication, Dr. Martin Groenewegen for providing his published data in electronic form, and an anonymous referee whose recommendations lead to considerable improvements in the paper. A large part of this work was done while JvL was a student at ESO and the University of Amsterdam. A Joaninha está sempre nas coisas mais importantes da vida.
© European Southern Observatory (ESO) 2000
Online publication: January 31, 2000