1. Raymond and Beverly Sackler Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, the Netherlands
2. Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, the Netherlands
3. INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125, Florence, Italy
4. Centre for Star and Planet Formation, Niels Bohr Institute & Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K., Denmark
5. Faculty of Aerospace Engineering, Delft University of Technology, NL-2629 HS Delft, the Netherlands
6. Max-Planck Institut für Extraterrestrische Physik (MPE), Giessenbachstr. 1, D-85748 Garching, Germany