The stellar content of NGC 346 - A plethora of O stars in the SMC

Abstract

The stellar content of NGC 346, the largest and brightest H II region inthe SMC, was investigated using the results of CCD UBV photometry andspectroscopy. Spectra of 42 blue stars were classified, showing that 33are of the O type, of which 11 are of type O6.5 or earlier, which is asmany early-type O stars known in the rest of the SMC. The resultsidentify 25-30 NGC 346 stars more massive than 25 solar masses, and sixstars more massive than 40 solar masses, indicating that the upper-masscutoff to the IMF is not lower in the SMC than in the Galaxy or the LMC.The presence of evolved 15 solar-mass stars in the NGC 346 indicatesthat some massive stars formed 15 million yr ago. The results of spatialdistribution suggest that star formation began at the southwest side ofthe association and has spread to where the central cluster lies now,providing an example of sequential star formation in the SMC.