1. INAF – Osservatorio Astronomico di Brera; via Bianchi 46; I-23807; Merate (LC); Italy
2. SUPA (Scottish Universities Physics Alliance), Institute for Astronomy; University of Edinburgh; Royal Observatory, Blackford Hill; Edinburgh; EH9 3HJ
3. Max-Planck Institut für Astrophysics; D-85748; Garching bei München; Germany