1. National Observatory of Athens, Lofos Nymfon, 11852 Athens, Greece
2. Department of Physics, National Technical University of Athens, Zografou Campus, 15773 Athens, Greece
3. CAS Key Laboratory for Researches in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei 230026, China
4. Departamento de Matemáticas, Universidad Católica del Norte, Avda. Angamos 0610, Casilla, Antofagasta 1280, Chile