1. Department of Physics, University of the Free State , PO Box 339, Bloemfontein 9300, South Africa
2. School of Physical Sciences and Centre for Astrophysics & Relativity, Dublin City University , Glasnevin, D09 W6Y4, Ireland
3. Institut für Astronomie und Astrophysik Tübingen, Universität Tübingen , Sand 1, D-72076 Tübingen, Germany
4. Dublin Institute for Advanced Studies , 31 Fitzwilliam Place, Dublin 2, Ireland
5. School of Physics, University of the Witwatersrand , 1 Jan Smuts Avenue, Braamfontein, Johannesburg 2050 South Africa
6. South African Astronomical Observatory , PO Box 9, Observatory, 7935 Cape Town, South Africa
7. Department of Astronomy, University of Cape Town , Private Bag X3, Rondebosch 7701, South Africa