[1] Univ Sheffield, Dept Phys & Astron, Sheffield S3 7RH, S Yorkshire, England
[2] Univ Warwick, Dept Phys, Coventry CV4 7AL, W Midlands, England
[3] Royal Observ Edinburgh, UK Astron Technol Ctr, Edinburgh EH9 3HJ, Midlothian, Scotland
[4] Liverpool John Moores Univ, Astrophys Res Inst, Liverpool L3 5RF, Merseyside, England
[5] Natl Astron Res Inst Thailand, Chiang Mai 50200, Thailand
[6] European So Observ, D-85748 Garching, Germany
[7] Univ Oxford, Dept Phys, Oxford OX1 3RH, England
[8] Lyncaeus Ltd, Barnard Castle DL12 8JD, County Durham, England