1. Scottish Universities Physics Alliance, Institute for Astronomy; University of Edinburgh, Royal Observatory; Blackford Hill; Edinburgh; EH9 3HJ
2. Department of Physics and Astronomy; University of British Columbia; 6224 Agricultural Road; Vancouver; BC; V6T 1Z1; Canada
3. Department of Physics; Oxford University; Keble Road; Oxford; OX1 3RH
4. Argelander Institute for Astronomy; University of Bonn; Auf dem Hügel 71; 53121; Bonn; Germany
5. Institut d’Astrophysique de Paris; Université Pierre et Marie Curie - Paris 6; 98 bis Boulevard Arago; F-75014; Paris; France
6. Institut de Ciencies de l’Espai; CSIC/IEEC; F. de Ciencies, Torre C5 par-2; Barcelona; 08193; Spain
7. Institute of Astronomy and Astrophysics; Academia Sinica; PO Box 23-141; Taipei 10617; Taiwan
8. Key Lab for Astrophysics; Shanghai Normal University; 100 Guilin Road; 200234; Shanghai; China
9. Leiden Observatory; Leiden University; Niels Bohrweg 2; 2333; CA Leiden; the Netherlands