[1] Univ Padua, Dipartimento Astron, I-35122 Padua, Italy
[2] European So Observ, D-85748 Garching, Germany
[3] Rice Univ, Dept Phys & Astron, Houston, TX 77005 USA
[4] Univ Washington, Dept Astron, Seattle, WA 98195 USA
[5] Osservatorio Astron Collurania, INAF, I-64100 Teramo, Italy
[6] Osserv Astron Padova, INAF, I-35122 Padua, Italy