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