1. Department of Physics and Astronomy, Clemson University , Kinard Lab of Physics, Clemson, SC 29634-0978 , USA
2. Leiden Observatory, Leiden University , PO Box 9513, NL-2300 RA Leiden , the Netherlands
3. IPARCOS and Department of EMFTEL, Universidad Complutense de Madrid , E-28040 Madrid , Spain
4. Julius-Maximilians-Universität , Würzburg D-97070 , Germany
5. Instituto de Astrofísica de Canarias (IAC) , E-38200 La Laguna, Tenerife , Spain
6. Universidad de La Laguna (ULL), Departamento de Astrofísica , E-38206 La Laguna, Tenerife , Spain
7. Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n , E-18008 Granada , Spain
8. Department of Physics, Yale University , 52 Hillhouse Avenue, New Haven, CT 06511 , USA