Date Presented:

2013/06/1

Abstract:

The Small Magellanic Cloud (SMC) is a well known laboratory for studies of High-Mass X-ray Binaries (HMXBs), that are prime targets to investigate the evolution of binaries and massive stars. Although the number of identified Be X-ray Binaries (BeXRBs) has increased dramatically in the last decade, only recently we started to obtain a better picture of their their spectral-type distributions, which in turn can provide us with information and constrains regarding their evolution and nature. We present results from a systematic spectroscopic campaign of HMXBs identified in Chandra and XMM-Newton surveys of the SMC, using the AAOmega/2dF spectrograph at the the Anglo-Australian Telescope. We classified 21 sources, one of which is the well known supergiant B[e] star S18 (or AzV 154). We suggest that it is the optical counterpart of the X-ray source CXOU J005409.57-724143.5, being the second supergiant X-ray binary in the SMC since 1971. The classified sources are within a wide range of five orders of X-ray luminosity, extending our census of BeXRBs to almost quiescent luminosities. A comparison of the populations of HMXBs in the SMC and the Milky Way with respect to their spectral types and orbital parameters (periods and eccentricities) shows no evidence for difference in their populations. In order to expand the sample of HMXBs we performed a systematic survey on selected active regions of the SMC. Since the optical counterparts of the HMXBs display Hα excess they can be identified through Hα imaging. Thus, we observed 16 regions with the Wide Field Imager at MPG/ESO and the MOSAIC II Imager at CTIO Blanco telescopes. The analysis of these data yields approximately 3000 identified Hα emitting stars in the most active regions of the SMC. We discuss the photometric parameters of these sources (Hα EW, broad-band optical and IR colors), and their correlation with the X-ray sources identified in the Chandra and XMM-Newton surveys.

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