1. Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
2. Nordita, KTH Royal Institute of Technology and Stockholm University, Hannes Alfvéns väg 12, Stockholm SE-106 91, Sweden
3. Astroinformatics, Department of Computer Science, Aalto University, PO Box 15400, Espoo FI-00076, Finland
4. School of Mathematics, Statistics and Physics, Newcastle University, Newcastle upon Tyne NE1 7RU, UK