[1] INAF Osservatorio Astron Palermo, I-90134 Palermo, Italy
[2] Smithsonian Astrophys Observ, Cambridge, MA 02138 USA
[3] Univ Hertfordshire, CAR STRI, Hatfield AL10 9AB, Herts, England
[4] Univ La Laguna, Dept Astrofis, D-38206 San Cristobal la Laguna, Tenerife, Spain
[5] Grantecan CALP, E-38712 Brena Baja, La Palma, Spain
[6] Inst Astrofis Canarias, E-38205 San Cristobal la Laguna, Tenerife, Spain
[7] Boston Coll, Inst Sci Res, Newton, MA 02459 USA