1. Department of Astronomy and Physics, Saint Mary’s University , 923 Robie Street, Halifax, NS B3H 3C3 , Canada
2. Department of Astronomy, University of Michigan , 1085 South University Avenue, Ann Arbor, MI 48109-1107 , USA
3. IRAP, Université de Toulouse , CNRS, UPS, CNES, 9 Avenue du Colonel Roche, BP 44346, F-31028 Toulouse Cedex 4 , France
4. INAF – Osservatorio Astrofisico di Arcetri , Largo Enrico Fermi 5, I-50125 Firenze , Italy
5. Dipartimento di Matematica e Fisica, Universitá Roma Tre , via della Vasca Navale 84, I-00146 Rome , Italy