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Hα imaging for BeXRBs in the Small Magellanic Cloud

Published online by Cambridge University Press:  28 July 2017

G. Maravelias
Affiliation:
Astronomický ústav AVČR, v.v.i., Ondřejov, Czechia, email: maravelias@asu.cas.cz
A. Zezas
Affiliation:
Department of Physics, University of Crete, Heraklion, Greece Harvard-Smithsonian Center for Astrophysics, Cambridge, USA Foundation for Research and Technology-Hellas (FORTH), Heraklion, Greece
V. Antoniou
Affiliation:
Harvard-Smithsonian Center for Astrophysics, Cambridge, USA
D. Hatzidimitriou
Affiliation:
Department of Physics, University of Athens, Greece
F. Haberl
Affiliation:
Max-Planck-Institut für extraterrestrische Physik, Garching, Germany
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Abstract

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The Small Magellanic Cloud (SMC) hosts a large number of high-mass X-ray binaries, and in particular of Be/X-ray Binaries (BeXRBs; neutron stars orbiting OBe-type stars), offering a unique laboratory to address the effect of metalicity. One key property of their optical companion is Hα in emission, which makes them bright sources when observed through a narrow-band Hα filter. We performed a survey of the SMC Bar and Wing regions using wide-field cameras (WFI@MPG/ESO and MOSAIC@CTIO/Blanco) in order to identify the counterparts of the sources detected in our XMM-Newton survey of the same area. We obtained broad-band R and narrow-band Hα photometry, and identified ~10000 Hα emission sources down to a sensitivity limit of 18.7 mag (equivalent to ~B8 type Main Sequence stars). We find the fraction of OBe/OB stars to be 13% down to this limit, and by investigating this fraction as a function of the brightness of the stars we deduce that Hα excess peaks at the O9-B2 spectral range. Using the most up-to-date numbers of SMC BeXRBs we find their fraction over their parent population to be ~0.002 − 0.025 BeXRBs/OBe, a direct measurement of their formation rate.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2017 

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