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		| Paper: | 
		Hot Subdwarfs | 
	 
	
		| Volume: | 
		318, Spectroscopically and Spatially Resolving the Components of Close Binary Stars | 
	 
	
		| Page: | 
		387 | 
	 
	
		| Authors: | 
		Maxted, P.F.L. | 
	 
	
	
		| Abstract: | 
		Hot subdwarfs can be divided broadly into subdwarf O-stars (sdO) and subdwarf-B stars (sdB). The majority of sdB stars are extreme horizontal branch (EHB) stars, i.e., core-helium burning stars with a mass close to 0.5 Solar masses and with a very thin, inert hydrogen envelope. It has recently been discovered that most sdB stars are spectroscopic binaries with orbital periods of hours or days. I review the observed properties of these binaries and discuss the constraints these observations impose on models for the formation of the EHB stars. The sdO stars are a heterogeneous group. I highlight some recent results for binary sdO stars. | 
	 
	
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