This work was supported by the NASA Astrophysics Theory Program under grant NAG5-3027 (Z.E.M. and P.U.), by NASA/MSFC under grant NAG8-839 (Z.E.M.), by NSF under grant ATM-9526196 (Z.E.M.), and by NATO under grant CRG-910058 (P.U. and Z.E.M.). Z.E.M. also acknowledges the support of this work by the Alexander von Humboldt Foundation. The authors thank W. Rammacher for help with the numerical code and S.R.O. Ploner for help with the manuscript.
© European Southern Observatory (ESO) 1998
Online publication: September 8, 1998