[1] Univ Tubingen, Inst Astron & Astrophys, Theoret Astrophys, D-72076 Tubingen, Germany
[2] Univ Fed Paraiba, Dept Fis, Caixa Postal 5008, BR-58051 Joao Pessoa, Paraiba, Brazil
[3] Univ Estadual Ceara, Grp Fis Teor GFT, UECE FECLI, Iguatu, CE, Brazil
[4] Univ Estadual Ceara, Ctr Ciencias & Tecnol, Grp Fis Teor GFT, BR-60714903 Fortaleza, Ceara, Brazil