1. Group of Astrophysics, UMCS, E. Radziszewskiego 10, 20-031 Lublin, Poland
2. Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital-263 129, India
3. Department of Physics, Indian Institute of Technology (IIT)-BHU, Varanasi-221005, India
4. Department of Physics, University of Texas at Arlington, Arlington, TX 76019, USA
5. Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, 79104 Freiburg, Germany