We have initiated single-dish monitoring observations of 400 methanol maser sources at 6.7 GHz using the Hitachi 32-m radio telescope from December 2012 to systematically research periodic ux variations, which are observed in some methanol maser sources associated with high-mass (proto-)stars. In our monitoring, we have made daily monitoring, so that each source has been observed every nine days with an integration time of 5 min (typical 3  detection sensitivities of 0.9 Jy). The monitoring observations help us statistically understand periodic ux variations with a period longer than 50 days. As an initial result, we present a new detection of periodic ux variations in the 6.7 GHz methanol maser source G 036.70+00.09. The period of the ux variations is ~53 days (~0.019 cycles day-1), and seems to be stable over 9 cycles, at least until the middle of August 2014.

ABSTRACT
1. INTRODUCTION
2. OBSERVATIONS
3. RESULTS AND CONCLUSIONS
REFERENCES

• Koichiro Sugiyama(Center for Astronomy, Ibaraki University)
• Yoshinori Yonekura(Center for Astronomy, Ibaraki University)
• Kazuhito Motogi(The Research Institute for Time Studies, Yamaguchi University)
• Yu Saito(College of Science, Ibaraki University)
• Kenta Fujisawa(The Research Institute for Time Studies, Yamaguchi University)
• Shota Ishii(College of Science, Ibaraki University)
• Munetake Momose(College of Science, Ibaraki University)
• Mareki Honma(Mizusawa VLBI Observatory)
• Fumie Tazaki(Mizusawa VLBI Observatory)
• Kei E. I. Tanaka(Department of Astronomy, University of Florida)
• Takashi Hosokawa(Department of Physics and Research Center for the Early Universe, The University of Tokyo)
• Mizuho Uchiyama(Institute of Astronomy, Graduate School of Science, The University of Tokyo)
• Kohei Inayoshi(Department of Astronomy, Columbia University)