1. Osservatorio Astronomico di Bologna; INAF; Via C. Ranzani, 1; I-40127; Bologna; Italy
2. Departament d'Astronomia i Meteorologia; Institut del Ciènces del Cosmos (ICC); Universitat de Barcelona (IEEC-UB); c/Martí i Franquès, 1; 08028; Barcelona; Spain
3. Dipartimento di Astronomia; Università di Bologna; Via C. Ranzani, 1; I-40127; Bologna; Italy
4. Observatorio Astronómico Nacional; Universidad Nacional Autónoma de México; Apartado Postal 877, C. P.; 22800; Ensenada; BC; Mexico
5. Department of Physics and Astronomy; Notre Dame University Louiaze; PO Box 72; Zouk Mikael; Zouk Mosbeh; Lebanon
6. Kapteyn Institute; University of Groningen; PO Box 800; 9700; AV Groningen; the Netherlands
7. Institut d'Estudis Espacial de Catalunya; Edifici Nexus; c/Capitá, 2-4, desp. 201; E-08034; Barcelona; Spain