1. Physics Department and Biruni Observatory, College of Sciences, Shiraz University, Shiraz 71454, Iran
2. Research Institute for Astronomy and Astrophysics of Maragha (RIAAM), P.O. Box 55134-441, Maragha, Iran
3. Helmholtz-Institut Jena, Fröbelstieg 3, Jena D-07743 Germany