We thank the referee, Hy Spinrad, for his comments, which have improved the paper. We also thank Remco Slijkhuis for his help in using the ESO archive, and Hà Vuong for useful discussions. The W. M. Keck observatory is a scientific partnership between the University of California and the California Institute of Technology, made possible by the generous gift of the W. M. Keck Foundation. The National Radio Astronomy Observatory is operated by Associated Universities Inc., under cooperative agreement with the National Science Foundation. The work by C.D.B., W.v.B., D.M. and S.A.S. at IGPP/LLNL was performed under the auspices of the US Department of Energy under contract W-7405-ENG-48. DM is also supported by Fondecyt grant No. 01990440 and DIPUC.
© European Southern Observatory (ESO) 1999
Online publication: November 23, 1999