The author thanks Dr. Hans Rickman from Astronomical Observatory of the Uppsala University, Sweden, for providing the computer code for numerical integration of orbits. The work was supported, in part, by VEGA - the Slovak Grant Agency for Science (grant No. 5101). The numerical calculations were performed using computational resources (Origin 2000) of the Computing Centre of the Slovak Academy of Sciences.
© European Southern Observatory (ESO) 1999
Online publication: November 3, 1999