We thank Dave Graham for help with the observations in Effelsberg, Tony Beasley for asistance at the VLBA, and Mark Reid for useful comments on the text. M.J.R. wishes to acknowledge support for this research by the European Union under contract CHGECT920011. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
© European Southern Observatory (ESO) 2000
Online publication: March 9, 2000