[1] Max-Planck-Inst. E.P., PO Box 1312, Garching bei München 85741, Germany
[2] Lab. d'Astrophysique de Grenoble, Université Joseph-Fourier, BP 53, 38041 Grenoble Cedex 9, France
[3] Department of Astronomy, Odessa National University, T. G. Shevchenko park, 65014 Odessa, Ukraine
[4] Crimean Astrophysical Observatory, 98409 Nauchny, Ukraine
[5] Department of Physics, University of Leicester, Leicester LEI 7RH, United Kingdom