We thank the anonymous referee for careful reading and useful comments on the manuscript. We appreciate his suggestions regarding improvement of the revised version of the manuscript at various points. The authors wish to acknowledge their thanks to UP State Observatory, Nainital for providing library facilities and Anil K. Joshi for his cooperation towards preparing the latex version of this manuscript. This work is sponsored by CSIR, New Delhi, under the scientist's pool scheme.
© European Southern Observatory (ESO) 2000
Online publication: December 17, 1999