We are grateful to the UK Particle Physics and Astronomy Research Council for support of the project. The Mark 6 telescope was constructed with the assistance of the staff of the Physics Department, University of Durham, and the efforts of Mr. P. Cottle, Mrs. E.S. Hilton and Mr. K. Tindale are acknowledged with gratitude.
We would like to thank the anonymous referee for helpful comments.
© European Southern Observatory (ESO) 2000
Online publication: January 29, 2001