1. Inter-University Centre for Astronomy and Astrophysics Post Box No. 4, Ganeshkhind, Pune 411007, India
2. INAF, Osservatorio Astronomico di Brera, Via E. Bianchi 46, Merate (LC) I-23807, Italy
3. Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, Garching D-85748, Germany