[1] Univ Paris 07, UMR 8631, F-92195 Meudon, France
[2] CNRS, UMR 8631, F-92195 Meudon, France
[3] Observ Paris, DAEC, F-92195 Meudon, France
[4] Ruhr Univ Bochum, Lehrstuhl Theoret Phys 1, D-44780 Bochum, Germany
[5] Univ Metropolitana, Dept Fis, Caracas 1070A, Venezuela
[6] Inst Venezolano Invest Cient, Ctr Fis, Caracas 1020A, Venezuela