1. Veracruzanian University; Cto. Universitario los Lagos s/n Xalapa, Ver 91000 Mexico
2. National Institute for Astrophysics, Optics and Electronics; Luis E. Erro No. 1 Tonantzintla, Pue 72840 Mexico
3. New Mexico State University; 1600 Steward Street Las Cruces NM 88003 USA