1. School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
2. Kapteyn Astronomical Institute, Post Office Box 800, 9700 AV Groningen, Netherlands.
3. Istituto Nazionale di Astrofisica (INAF)–Astronomical Observatory of Capodimonte, via Moiariello 16, I–80131 Naples, Italy.
4. INAF-Astronomical Observatory of Pino Torinese, via Osservatorio 20, I–10025 Pino Torinese, Italy.
5. Leiden Observatory, Post Office Box 9513, 2300 RA Leiden, Netherlands.