1. Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
2. GEPI, Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, 5 place Jules Janssen, F-92190 Meudon, France
3. Station de Radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU USR 704, Université d’Orléans OSUC, route de Souesmes, F-18330 Nançay, France
4. South African Astronomical Observatory, PO Box 9, Observatory 7935, Cape Town, South Africa
5. INAF- Osservatorio Astronomico di Cagliari, Via della Scienza 5, I-09047 Selargius (CA), Italy
6. Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131, USA