1. Departamento de Física, Universidade Federal de Santa Maria, Centro de Ciências Naturais e Exatas, 97105-900, Santa Maria, RS, Brazil
2. Universidade Federal de Santa Maria, Colégio Politécnico, 97105-900, Santa Maria, RS, Brazil
3. Instituto de Física, Universidade Federal do Rio Grande do Sul, CP 15051, 91501-970, Porto Alegre, RS, Brazil
4. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
5. School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY 14623-5603, USA
6. Department of Physics and Astronomy, Georgia State University, Astronomy Offices, 25 Park Place, Suite 605, Atlanta, GA 30303, USA
7. Department of Astronomy, Universidad de Concepción, Casilla 160-C, Concepción, Chile
8. SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, NL-3584 CA Utrecht, the Netherlands
9. Department of Astrophysics/IMAPP, Radboud University, Nijmegen, PO Box 9010, NL-6500 GL Nijmegen, the Netherlands
10. Remote Sensing Division, Naval Research Laboratory, 4555 Overlook Avenue, SW, Washington, DC 20375, USA
11. Institute for Astrophysics and Computational Sciences, Department of Physics, The Catholic University of America, Washington, DC 20064, USA