1. European Southern Observatory, Karl-Schwarzschild-Straße 2, D-85748 Garching bei München, Germany
2. Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
3. INAF-Osservatorio di Astrofisica & Scienza dello Spazio, via Gobetti 93/3, I-40129 Bologna, Italy
4. Department of Astrophysics/IMAPP, silvia.martocchia@eso.org Radboud University, P.O. Box 9010, NL-6500 GL Nijmegen, the Netherlands