1. Dept. of Astrophysical & Planetary Sciences, Center for Astrophysics & Space Astronomy (CASA), CASA; University of Colorado; Boulder Colorado
2. Physikalisch-Meteorologisches Observatorium Davos & World Radiation Center (PMOD/WRC), PMOD; WRC; Davos Dorf Switzerland
3. Department of Astrophysics; University of Vienna; Vienna Austria
4. Institute of Astronomy & National Astronomical Observatory Bulgarian Acadamy of Sciences; Sofia Bulgaria