This paper is based on the MSc. thesis of one of the authors (del Peloso, 1996). E.F. del Peloso and L. da Silva acknowledge full financial support of this work by the CNPq/Brazil (grants of E. F. del Peloso and L. da Silva, numbers 131604/94.5 and 200580/97, respectively). G.F. Porto de Mello acknowledges the financial support of the Fundação Universitária José Bonifácio, CNPq and PRONEX/Finep (grant number 41.96.0908.00). The authors wish to thank Dr. G. Cayrel de Strobel for helpful discussions and comments. Finally, we thank L. Penalva for the reduction of some of the spectra, and the referee, Dr. D.R. Soderblom, for his remarks on the manuscript.
© European Southern Observatory (ESO) 2000
Online publication: June 26, 2000