Some of the data were obtained, and reduced during a research stay of CT at the Universidad Católica, Santiago, Chile. This was financially supported by the Deutscher Akademischer Austauschdienst (DAAD) under grant D/94/14720. We would also like to thank the referee, Dr. Lutz Wisotzki, for helpful comments.
© European Southern Observatory (ESO) 1999
Online publication: October 4, 1999