1. Astronomy and Astrophysics Group, Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
2. Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599-3255, USA
3. Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
4. Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, United Kingdom
5. Department of Physics, Texas Lutheran University, Seguin, TX 78155
6. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, United Kingdom
7. Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain