1. Department of Astronomy, University of Texas at Austin, 2515 Speedway, C1400, Austin, TX 78712, USA
2. Instituto de Física, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, 91501-900, Porto Alegre, RS, Brazil
3. Institute for Physics and Astronomy, University of Potsdam, Karl Liebknecht-Str 24/25, D-14476 Potsdam, Germany
4. Institute for Astrophysics, Georg-August-University, Friedrich-Hund-Platz 1, D-37077 Gottingen, Germany
5. Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
6. Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA
7. Dipartimento di Fisica e Astronomia ‘Galileo Galile’, Università di Padova, Vicolo dell’Osservatorio 3, I-35122, Padova, Italy
8. Istituto Nazionale di Astrofisica - Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122, Padova, Italy
9. Center for Gravitation, Cosmology, and Astrophysics, Dept. of Physics, Uni. of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA
10. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA