[1] Space Telescope Sci Inst, Baltimore, MD 21218 USA
[2] Univ Amsterdam, Astron Inst Anton Pannekoek, NL-1098 SJ Amsterdam, Netherlands
[3] Inst Astrofis Canarias, Tenerife 38200, Spain
[4] Univ La Laguna, Dept Astrofis, Tenerife 38205, Spain
[5] Univ Edinburgh, Royal Observ Edinburgh, Inst Astron, Scottish Univ Phys Alliance, Edinburgh EH9 3HJ, Midlothian, Scotland
[6] Royal Observ Edinburgh, UK Astron Technol Ctr, Edinburgh EH9 3HJ, Midlothian, Scotland
[7] Bulgarian Acad Sci, Natl Astron Observ, Inst Astron, Smoljan 4700, Bulgaria
[8] European Space Agcy, European Space Astron Ctr, Madrid 28691, Spain
[9] Katholieke Univ Leuven, Inst Sterrenkunde, B-3001 Louvain, Belgium