An X‐Ray Investigation of the NGC 346 Field in the Small Magellanic Cloud. II. The Field Population

We present results from a Chandra observation of the NGC346 cluster, which isthe ionizing source of N66, the most luminous HII region and the largest starformation region in the SMC. In the first part of this investigation, we haveanalysed the X-ray properties of the cluster itself and the remarkable star HD5980. But the field contains additional objects of interest. In total, 75 X-raypoint sources were detected in the Chandra observation: this is five times thenumber of sources detected by previous X-ray surveys. We investigate here theircharacteristics in detail. Due to high foreground absorption, the sourcespossess rather high hardness ratios. Their cumulative luminosity functionappears generally steeper than that for the rest of the SMC at higherluminosities. Their absorption columns suggest that most of the sources belongto NGC 346. Using DSS data and new UBVRI imaging with the ESO 2.2m telescope,we also discovered possible counterparts for 32 of these X-ray sources andestimated a B spectral type for a large number of these counterparts. Thistends to suggest that most of the X-ray sources in the field are in fact X-raybinaries. Finally, some objects show X-ray and/or optical variability, with aneed for further monitoring.Comment: 20 pages, 10 figures (3 in jpg), accepted by Ap