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		| Paper: | 
		VLBI phase-referencing for observations of weak radio sources | 
	 
	
		| Volume: | 
		19, Radio Interferometry: Theory, Techniques, and Applications, IAU Colloquium 131 | 
	 
	
		| Page: | 
		289 | 
	 
	
		| Authors: | 
		Lestrade, J.-F. | 
	 
	
	
		| Abstract: | 
		Phase-referencing is a technique used in VLBI to extend the signal coherence time from a few minutes to a few hours in order to enhance significantly its sensitivity. With this technique, VLBI observations of milliJansky radio sources can be conducted for high-accuracy differential astrometry as well as imaging. We describe the technique in some details and present, as an example, a submilliarcsecond differential astrometric experiment design to identify the star responsible for the weak radio emission in the binary system Algol. | 
	 
	
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