1. Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks St., Norman, OK 73019, USA
2. Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
3. Department of Physics and Astronomy, University of North Carolina, Chapel Hill NC 27599, USA
4. Facultad de Ciencias Astronómicas y Geofísicas (UNLP), La Plata, Argentina
5. Smithsonian Astrophysical Observatory, 60 Garden St, Cambridge MA 02138, USA
6. Dunlap Institute for Astronomy & Astrophysics, University of Toronto, 50 St. George Street, Toronto M5S 3H4, Canada
7. Astronomy and Astrophysics Group, Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK