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tokens: In this research, we have used and acknowledge with gratitude, the data from the AAVSO International Database, based on observations submitted to the AAVSO by variable star observers worldwide. A part of the data in this study was obtained from the NRO Data Archive System. The authors wish to express their gratitude to S. Oizumi, H. Yamamoto, S. Tanada, H. Toujima, T. Yasuda, Y. Arao, K. Ando, K. Ueda, D. Namikawa, N. Matsumoto, M. Kuroki, Y. Kodama, and M. Suzuki for their help with data analysis. We also acknowledge the contribution of Dr. S. Deguchi who provided us with scientific advice. Thanks to the referee for constructive comments.