1. Academia Sinica, Institute of Astronomy and Astrophysics, 11F Astronomy-Mathematics Building, NTU/AS campus, No. 1, Section 4, Roosevelt Rd., Taipei 10617, Taiwan
2. European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching b. München, Germany
3. Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK
4. Astronomy and Astrophysics Research Group, Dep. of Physics and Astrophysics, V.U. Brussel, Pleinlaan 2, B-1050 Brussels, Belgium
5. Institute of Theoretical Physics and Astrophysics, Universität zu Kiel, Leibnizstr. 15, D-24118 Kiel, Germany