1. Physics Department, North Bengal University, Darjeeling 734013, West Bengal, India
2. Department of Physics, Alipurduar College, Alipurduar Court, Jalpaiguri 736122, West Bengal, India
3. Department of Physics, North Bengal University, Darjeeling 734013, India
4. Inter-University Centre for Astronomy and Astrophysics, Ganeshkhind, Pune 411007, India