A. G. and A. H. thank the Austrian Academy of Sciences and the National Academy of Sciences of Ukraine for financing the exchange of scientists. A. H. thanks the `Austrian Fonds zur Förderung der wissenschaftlichen Forschung' for supporting these investigations. A. K and J. R. acknowledge the grant VEGA 2/7229/20 and the Austrian and Slovak Academy of Sciences.
© European Southern Observatory (ESO) 2000
Online publication: December 5, 2000