1. Space Research Institute (IKI), Profsoyuznaya 84/32, Moscow 117997, Russia
2. Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str 1, D-85741 Garching, Germany
3. Universitäts-Sternwarte, Fakultät für Physik, Ludwig-Maximilians-Universität München, Scheinerstr 1, D-81679 München, Germany
4. Ioffe Institute, 26 Politekhnicheskaya str, St. Petersburg 194021, Russia
5. Institute of Astronomy, Russian Academy of Sciences, 48 Pyatnitskaya str, Moscow 119017, Russia
6. Institute of Applied Physics of the Russian Academy of Sciences, 46 Ul’yanov str, Nizhny Novgorod 603950, Russia