An X-ray investigation of the NGC346 field in the SMC (1) : the LBV HD5980 and the NGC346 cluster

Abstract

We present results from a Chandra observation of the NGC346 cluster. This cluster contains numerous massive stars and is responsible for the ionization of N66, the most luminous HII region and the largest star formation region in the SMC. In this first paper, we will focus on the characteristics of the main objects of the field. The NGC346 cluster itself shows only relatively faint X-ray emission (with L_X^{unabs} ~ 1.5 times 10^{34} erg s^{-1}), tightly correlated with the core of the cluster. In the field also lies HD5980, a LBV star in a binary (or possibly a triple system) that is detected for the first time at X-ray energies. The star is X-ray bright, with an unabsorbed luminosity of L_X^{unabs} ~ 1.7 times 10^{34} erg s^{-1}, but needs to be monitored further to investigate its X-ray variability over a complete 19d orbital cycle. The high X-ray luminosity may be associated either with colliding winds in the binary system or with the 1994 eruption. HD5980 is surrounded by a region of diffuse X-ray emission, which is a supernova remnant. While it may be only a chance alignment with HD5980, such a spatial coincidence may indicate that the remnant is indeed related to this peculiar massive star.