B.N. Zega Department of Physics, University of Bengkulu, Jl. W.R. Supratman, Bengkulu 38122, Indonesia Indonesia
S. He Earth of Observatory of Singapore, Nanyang Technological University, Singapore 639798, Singapore Singapore
A.M. Lubis Department of Physics, University of Bengkulu, Jl. W.R. Supratman, Bengkulu 38122, Indonesia Indonesia