We gratefully thank the NRAO staff for its assistance during the remote observing sessions. We have used the SIMBAD database from the Centre de Données de Strasbourg (France) to retrieve bibliographic data, the Lyon-Meudon Extragalactic Database (LEDA) supplied by the LEDA team at the CRAL-Observatoire de Lyon (France), and of the NASA Extragalactic Database. We thank the referee, Leslie Sage, for useful suggestions.
© European Southern Observatory (ESO) 1998
Online publication: February 16, 1998