We are very grateful to Matthias Steinmetz for kindly allowing us the use of his SPHINX code, and to J. Auman, G. Fahlman, G. Lewis, T.K. Menon, H. Richer and D. Scott for helpful discussions. RAI expresses gratitude to the Killam Foundation (Canada) and to the Fullam Award for support.
© European Southern Observatory (ESO) 1998
Online publication: July 7, 1998