1. Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, H-1121 Budapest, Konkoly Thege út 15–17, Hungary
2. Instituto de Astrofísica de Canarias, Avenida Vía Láctea, 38205 La Laguna, Tenerife, Spain
3. Directorate of Science, ESTEC–ESA, PO Box 299, NL-2200 AG, Noordwijk, the Netherlands