Close binary stars are so close that one component has an effect on the evolution of the other. But how do they form and evolve? This is an unsolved problem. One speculation is that the binary is a part of a hierarchical triple and its orbit shrinks due to interaction with the third component. Therefore, searching for and investigating tertiary components, especially close-in ones, in close binary stars are important for understanding their origin, as well as to test theories of star formation and stellar dynamical interaction.

ABSTRACT
1. INTRODUCTION
2. THREE BINARY STARS ARE MONITORED
3. SUMMARY
REFERENCES

• First M. Wenping Liao(Yunnan Observatories, Chinese Academy of Sciences/Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences)
• Shengbang Qian(Yunnan Observatories, Chinese Academy of Sciences/Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences/University of Chinese Academy of Sciences)
• Liying Zhu(Yunnan Observatories, Chinese Academy of Sciences/Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences/University of Chinese Academy of Sciences)
• Liang Liu(Yunnan Observatories, Chinese Academy of Sciences/Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences/University of Chinese Academy of Sciences)