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		| Paper: | 
		The Period Corrections of Two W UMa-type Binaries: V520 Cas and V680 Per | 
	 
	
		| Volume: | 
		451, 9th Pacific Rim Conference on Stellar Astrophysics | 
	 
	
		| Page: | 
		159 | 
	 
	
		| Authors: | 
		Wang, J.; Qian, S. | 
	 
	
	
		| Abstract: | 
		All available CCD light minimum times of two W UMa-type eclipsing binaries V520 Cas and V680 Per were collected from the literature. With the analysis of the O-C diagram, it is found that the values of their periods are inaccurate. We revised the orbital periods and obtained the new ephemeris. After that, the O-C values were recalculated, and it was discovered that the orbital period of V520 Cas shows a continuous decrease at a rate of  dP/dt=–6.35×10–7 days yr-1. The period of V680 Per was improved and shows no obvious variation. This work is much more meaningful to investigate on their period changes. | 
	 
	
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