This work was supported in part by the Deutsche Forschungsgemeinschaft (DFG), project number WA 1047/2-1, by the National Science Foundation (NSF), grant AST98-02802, and by the Australian Research Council (ARC, grant X00001713). It is a pleasure to thank the APO observers who helped obtaining this data, in particular K. Gloria, N. C. Hastings, D. Long, E. Bergeron, C. Corson, and R. McMillan. We also like to thank Rolf Stabell for his careful reading and his comments which helped to improve the paper.
© European Southern Observatory (ESO) 2000
Online publication: October 30, 2000