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		| Paper: | The Contribution of Faint, Failed, and Defunct Stars to the “Stellar” Masses of Galaxies |  
		| Volume: | 514, Stellar Populations and the Distance Scale |  
		| Page: | 79 |  
		| Authors: | Schechter, P. L. |  
		| Abstract: | A substantial fraction the stellar mass attributed to galaxies is invisible: stars close to the hydrogen-burning limit, brown dwarfs, white dwarfs, neutron stars, and black holes.  These constituents do, however, gravitationally micro-lens background quasars, thereby permitting measurement of the total stellar contribution to the mass surface density along the line of sight.  We report the results of such a measurement using a sample of ten quadruply lensed quasars.  We discuss the prospects for improving upon this measurement with a larger sample and describe efforts to find new quadruple lenses.  If we invert our argument and take the stellar mass to be known, we derive a value for the fraction of the dark halo in Massive Compact Halo Objects, or MaCHOs (including ∼20 M☉ primordial black holes), of something less than 10%, confirming the widely ignored result of Mediavilla et al. (2009). |  
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