1. Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, P-4150-762 Porto, Portugal
2. Centre for Space Research, North-West University, Potchefstroom 2520, South Africa
3. Instituto de Astronomía y Meteorología, Av, Vallarta 2602. Col. Arcos Vallarta. Guadalajara, Jalisco. C.P. 44130, México
4. Department of Astronomy, Universidad de Concepción, Casilla 160-C, Concepción, Chile