[1] Univ Catania, Dipartimento Fis & Astron, Viale Andrea Doria 6, I-95125 Catania, Italy
[2] Russian Acad Sci, Inst Astron, Pyatnitskaya Str 48, Moscow 119017, Russia
[3] Lanzhou Univ, Inst Theoret Phys, Sch Phys Sci & Technol, 222 South Tianshui Rd, Lanzhou 730000, Peoples R China
[4] Univ Lisbon, Inst Astrofis & Ciencias Espaco, Fac Ciencias, Ed C8, P-1769016 Lisbon, Portugal
[5] Lanzhou Univ, Lanzhou Ctr Theoret Phys, Key Lab Theoret Phys Gansu Prov, Lanzhou 730000, Peoples R China