We are very grateful to A. Biviano, D. Fadda and E. Slezak for making their software available to us. W. Forman and C. Jones thank the IAP for its hospitality and acknowledge support from the Smithsonian Institution and NASA contract NAS8-39073. We thank A. Loeb and U. Pen for helpful discussions.
© European Southern Observatory (ESO) 1998
Online publication: June 12, 1998