[1] Univ Munich, Sternwarte, D-81679 Munich, Germany
[2] Hamburger Sternwarte, D-21029 Hamburg, Germany
[3] Natl Opt Astron Observ, Tucson, AZ 85726 USA
[4] Special Astrophys Observ, Nizhni Arkhyz 357147, Karachai Circes, Russia
[5] Main Astron Observ, UA-03680 Kiev 127, Ukraine
[6] Tel Aviv Univ, Wise Observ, IL-69978 Tel Aviv, Israel
[7] CSIC, Inst Astrofis Andalucia, E-18080 Granada, Spain
[8] Observ Paris, Dept Radioastron ARPEGES, F-92195 Meudon, France