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		| Paper: | 
		The Stellar Population of Ultracompact HII Regions: the Case of IRAS 10049-5657 | 
	 
	
		| Volume: | 
		267, Hot Star Workshop III: the Earliest Stages of Massive Star Birth | 
	 
	
		| Page: | 
		343 | 
	 
	
		| Authors: | 
		Bik, A.; Kaper, L.; Hanson, M. M.; ComerĂ³n, F. | 
	 
	
	
		| Abstract: | 
		We have performed a near-infrared survey of 45 ``southern'' UCHII's and identified the deeply embedded, ionizing stars using VLT/ISAAC K-band spectroscopy. The (photospheric) spectra of these young massive stars allow the secure classification of their photospheric properties. As an example, we discuss the UCHII IRAS 10049-5657, which hosts a young cluster of stars. Two of the cluster members are classified as O4/O5 and O6, respectively. With this classification, the cluster ZAMS and distance is calibrated. The cluster consists of several dozen OB stars and likely is a recently formed OB association. | 
	 
	
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