[1] Univ Nacl Autonoma Mexico, Inst Astron, Ensenada 22830, Baja California, Mexico
[2] Texas Christian Univ, Dept Phys & Astron, Ft Worth, TX 76109 USA
[3] Univ Veracruzana, Fac Fis & Inteligencia Artificial, Xalapa 91000, Veracruz, Mexico
[4] Univ Manchester, Dept Phys & Astron, Jodrell Bank Observ, Macclesfield SK11 9DL, Cheshire, England
[5] Univ Nacl Autonoma Mexico, Mexico City 04510, DF, Mexico
[6] Univ Nacl Autonoma Mexico, Inst Ciencias Fis, Cuernavaca 62210, Morelos, Mexico