1. Physics Department, University of Johannesburg , 5 Kingsway Ave, Rossmore, Johannesburg, 2092 , South Africa
2. Inter-University Institute for Data Intensive Astronomy, Department of Astronomy, University of Cape Town , Rondebosch 7701 , South Africa
3. European Southern Observatory , Karl-Schwarzschild-Str 2, D-85748 Garching bei München , Germany
4. Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg , Mönchhofstraße 12-14, D-69120 Heidelberg , Germany
5. Dunlap Institute for Astronomy and Astrophysics, University of Toronto , 50 St George Street, Toronto ON, M5S 3H4 , Canada
6. Department of Physics & Astronomy, The University of British Columbia , 6224 Agricultural Road, Vancouver, BC V6T 1Z1 , Canada
7. School of Mathematics, Statistics and Physics, Newcastle University , Newcastle upon Tyne, NE1 7RU , UK