1. European Southern Observatory, Karl-Schwarzschild Str. 2, D-85748, Garching bei München, Germany
2. Department of Physics and Astronomy, University of the Western Cape, Bellville 7535, South Africa
3. Astrophysics, Department of Physics, Keble Road, Oxford OX1 3RH, UK
4. Department of Physics and Electronics, Rhodes University, PO Box 94, Grahamstown 6140, South Africa