1. Department of Physics, Kansas State University , 116 Cardwell Hall, Manhattan, KS 66506 , USA
2. E. Kharadze Georgian National Astrophysical Observatory , 47/57 Kostava St, Tbilisi 0179 , Georgia
3. School of Natural Sciences and Medicine, Ilia State University , 3/5 Cholokashvili Avenue, Tbilisi 0162 , Georgia
4. Instituto de Astrofísica de Andalucía (CSIC) , Glorieta de la Astronomía, E-18080 Granada , Spain