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We present new identifications of infrared counterparts to the population ofhard X-ray sources near the Galactic center detected by the Chandra X-rayObservatory. We have confirmed 16 new massive stellar counterparts to the X-raypopulation, including nitrogen-type (WN) and carbon-type (WC) Wolf-Rayet stars,and O supergiants. For the majority of these sources, the X-ray photometry isconsistent with thermal emission from plasma having temperatures in the rangeof kT=1-8 keV or non-thermal emission having power-law indices in the range of-1<gamma<3, and X-ray luminosities in the range of Lx~1e32-1e34 erg/s. Severalsources have exhibited X-ray variability of several factors between separateobservations. The X-ray properties are not a ubiquitous feature of singlemassive stars but are typical of massive binaries, in which the high-energyemission is generated by the collision of supersonic winds, or by accretiononto a compact companion. However, the possibility of intrinsic hard X-raygeneration from single stars cannot be completely ruled out. The spectralenergy distributions of these sources exhibit significant infrared excess,attributable to free-free emission from ionized stellar winds, supplemented byhot dust emission in the case of the WC stars. With the exception of one objectlocated near the outer regions of the Quintuplet cluster, most of the new starsappear isolated or in loose associations. Seven hydrogen-rich WN and O starsare concentrated near the Sagittarius B HII region, while other similar starsand more highly evolved hydrogen-poor WN and WC stars lie scattered within ~50pc, in projection, of Sagitarrius A West. We discuss various mechanisms capableof generating the observed X-rays and the implications these stars have formassive star formation in the Galaxy's Central Molecular Zone.

Near-infrared counterparts to Chandra X-ray sources toward the Galactic Center. II. Discovery of Wolf-Rayet stars and O supergiants